Braking in iRacing

[pro bono1984]

Hello,

I have a question about the braking in iRacing and it'd be great if someone could answer this.
I understand that iRacing is newer and supposedly better so maybe I'd like to try in the future.

In all sim games, there has to be a max braking pressure value/percentage because most users' braking works with travel, rather than pressure.
If all users had hydraulic pedals, there'd be no need for any max % but that's not the case obviously.

Since I've heard that you can't decrease/increase the max value in iRacing, I'd like to know if possible, how do the cars behave when absolutely piling on the brakes?
In other words, how is the threshold braking in iRacing?

I understand that the linearity is customisable but iRacing cannot be modded so I was wondering.

It seems degressive braking is there in iRacing, but in most sim games, there's no threshold braking (that's when you first apply brake pressure as quickly as you can without locking the brakes).

And I've recently learned that in real life motorsports that is one of the most difficult things to get right if you are to achieve a fast laptime (according to an instructer from a formula racing school).

I've checked out some FAQ sites and stuff but way too much info on the internet plus English isn't my first language so I thought this'd be better.

But more importantly, it's better to hear from real people, since there's lots of dubious info by those "I've never raced that car in RL but I know the physics is off" people.
I kind of doubt they've seriously raced in iRacing.

Cheers.

[brabham67]

It does it quite well, and they behave as I would expect them too, imo. With the right pedal setup threshold braking is achievable. I use a G27 wheel and pedals. The pedals have been modded with the Bodnar Cable(to increase resolution), and the NIXIM mod(to simulate a progressive feel).

I adjust the brake curve for each car so that the brakes lock up just past the point in the pedals throw where you hit the soft rubber stopper from the NIXIM mod. I find that I can easily modulate brake pressure with this setup, getting the maximum braking without lock up. It's not an easy thing to do with a potentiometer type brake, like mine.

Load cell and hydraulic pedal systems are far superior to getting the most out of braking in any sim, and make it far easier to maintain and control the balance of the car under braking.

EDIT: Disclosure I'm not a real life racer, but I am a real person.

[pro bono1984]

Thanks for responding. I like your f*k yea avatar btw.

So the brake curve thing is adjustable but the overall pressure percentage like the somewhat arbitrary 100% is not, am I correct?

By adjusting the lock-up point you mean for all of the cars you've tried so far, would you say?

I play GTR2 mostly and have tried rFactor demo that came with my G27 and I think it's a modified production car and its brakes made a brake hiss sound but no tyre screeching or lock-up but it's very moddable and iracing is not so I was just wondering.

Anyway thanks again.

[brabham67]

Originally Posted by pro bono1984

So the brake curve thing is adjustable but the overall pressure percentage like the somewhat arbitrary 100% is not, am I correct?

The brake curve adjustment is sort of a sensitivity adjustment. The 100% lock up point is most determined by the dev, based on the cars specs. Obviously stomping on the brakes at full speed has a different effect than stomping on them at lower speeds. It's all determined by the physics of the cars and the simulation. iRacing is quite good in this respect.

Primarily, iRacing is a multiplayer sim, as opposed to the rest which are primarily single player with a strong multiplayer component. iRacing is non moddable because they provide the environment in which to race.

[pro bono1984]

THank you brabham67.

I'm looking to drive the modified production cars or slower cars, so would you say if you slam on the brakes (100% travel braking), an instant lock-up for ALL those cars?

If not, the realism kind of fades away because, as I posted on the GTR2 braking thread, I'm practising threshold braking with my extra stiff brake pedal.

[MINIMM]

The braking is fine in iRacing, you can slam on the brakes if you wish and lock the brakes.

I haven't done real racing on a track, but I have done track days and the braking in iRacing is pretty realistic.

I do used CST's pedals (load cell) with the stiff brake upgrade.

[pro bono1984]

Thank you Mr MINIMM.
Good to know.

[AllanGP]

Braking in iRacing is very good imho and the adjustments available allow you to fine tune to your requirements/your brake set up well.

I use a G25 had no issues getting the Sim to do what I want.

I am however saving up my pocket money for one of Mr Speares hydraulic pedal sets! Which will help. Hydraulic pedals sets are being developed principly because iRacing has created a market for them, that in itself tells you what you need to know about iRacings braking set up.

[pro bono1984]

Thank you for your reply.

I just wouldn't like it if I had to "brake to the plastic" most of the time, like in some sim games.

If all the iracing cars' brakes in fact lock up when you mess up your initial threshold braking, it's totally understandable that now there are more and more realistic brake pedals available because of iracing.

And if that's the case, it's revolutionary and awesome for sim racing in general.

I'm looking to drive the mx-5, jetta and maybe the Ford GT and vette.
As for the open wheelers, I don't like them much because most of them're too fast for me, but definitely the skippy and maybe star mazda.

If those cars have a lockup point around or before say 80%, then that means kick the pedal and an instant lockup, but I thought otherwise because I rarely saw lockup in iracing videos.

So that just simply means iRacers are really that good yes?

[darock]

Originally Posted by pro bono1984

If those cars have a lockup point around or before say 80%, then that means kick the pedal and an instant lockup, but I thought otherwise because I rarely saw lockup in iracing videos.

Your comment about rarely seeing lockup gave me pause.

So I just went in and did some lockups with different cars. Most of the open wheelers will show the tires stop rolling, but the couple I tried didn't smoke the tires. I did get smoke off the SK mod tires however and really good smoke off the Nationwide car. It's apparently not a given they all smoke.

[pro bono1984]

Thank you darock.

So all of them lock-up instantly but some cars' tyres produce no or less smoke right?

So maybe afterall in iracing even those fast cars' brakes lock up?

I thought it'd be weird unless you have a 50kg pressure pedal or something, because otherwise for most of the users with potentiometer pedals, just a touch of brake would result in lockup at low speeds due to a lot less downforce and that could well be frustrating...

If all this is in fact true, that's a giant step forward for sim racing I'd say.....

[AllanGP]

Smoke isn't always present but you can lock up the brakes in every car no issue with the right settings, I'm not saying every one at 80% but around there.

In the HPD which has awesome brakes I can go hard on the pedal from full speed but have to modulate the pressure as the speed comes off otherwise they will lock up. At lower speeds if you brake too hard they lock up straight away.

[Kalifen]

Originally Posted by AllanGP

In the HPD which has awesome brakes I can go hard on the pedal from full speed but have to modulate the pressure as the speed comes off otherwise they will lock up. At lower speeds if you brake too hard they lock up straight away.

And this I assume is with the medium brake pressure setting? With hard you should lock up easily at full speed as well.


EDIT: For those that aren't familiar with iRacing yet, only a selected few cars have setup options for brake pressure. However, most can adjust brake balance.

[AllanGP]

Well I have only been running Fixed sets so I have not used that option but even with fixed sets I can adjust the brake curve if I want (but I have never had to from the original setting I chose).

Basically I don't see a braking issue in iRacing.

[Chronus]

Originally Posted by AllanGP

Basically I don't see a braking issue in iRacing.

I agree. There used to be a problem with the tire smoke generation (some said "graphics problem" but there was a good discussion explaining this was a result of something in the tire model). I can't verify if it is still there or not, though.

Braking in iRacing seems ok.

[Tony74]

The Corvette C6R is far too over-sensitive on the brakes, wheras the Riley Daytona Prototype feels about right to me.
I'd recommend going for only newer NTM cars (New Tyre Model) with a few exceptions such as the Riley DP.
The VW Jetta is still on the OTM, but that should be sorted out in this coming build. Some old cars respond better than others when they get the NTM.
However, if I was a person looking into a high quality sim right now I'd just wait for Assetto Corsa to be released. It will have superior physics and still have laser-scanned tracks. I'd play rFactor 2 in the meantime. iRacing can cost far too much considering the serious flaws in the physics.

[pro bono1984]

I'm glad to hear all this. Thank you guys!!

So iRacing IS much more advanced when it comes to braking physics...
Of course that's not to say GTR2 is unrealistic or arcade it's just that it was marketed for the then vast majority of users with soft potentiometer pedals.

Originally Posted by Tony74

The Corvette C6R is far too over-sensitive on the brakes, wheras the Riley Daytona Prototype feels about right to me.

Could it be that the sensitvity of the brakes is dependant on the pedal/hardware? So by using a stiffer pedal the linearity setting becomes more effective (less of an on/off brake pedal) and therefore it can sort this out maybe, because I've heard most real race cars' brake pedals take lots of pressure to lock up...

Originally Posted by Tony74

However, if I was a person looking into a high quality sim right now I'd just wait for Assetto Corsa to be released. It will have superior physics and still have laser-scanned tracks. I'd play rFactor 2 in the meantime. iRacing can cost far too much considering the serious flaws in the physics.

I try to be open to criticism and never be a fanboy of anything.
So could you elaborate on the flaws a little?
Is it serious enough to prevent a new user from enjoying it in your opinion?

[AllanGP]

A key question regardless of pro's and con's is how important is on-line racing to you, with real people?

If that is important iRacing is the place to go.

If it is not important other titles may suit you better, that is not to say iRacing may not still suit you as well.

iRacing subs wise is not expensive if you take the deals. The cost in your first year or two is in tracks and cars, mainly only if you are trigger happy. If you have defined goals again the costs can be managed - but it will be expensive compared to one off alternative game costs. Once you have the tracks and cars you want iRacing is really very cheap for what you get, not least 4 decent upgrades per year.

Having said the above as a "hobby" it is not expensive at all compared to some. (I assuming here you won't be going and buying a motion cockpit!!).

[Chronus]

Originally Posted by pro bono1984

So iRacing IS much more advanced when it comes to braking physics...
Of course that's not to say GTR2 is unrealistic or arcade it's just that it was marketed for the then vast majority of users with soft potentiometer pedals.

Not, that should not say GTR2 is unrealistic because it is not. Regardless of the customization imposed by SIMBIN, it was built upon isiMotor2 and obviously this is a great platform (and much more advanced than most people say it is).

Another thing to consider is that the pedal input (whether throttle, clutch or brake) and its treatment does not say anything in particular about its physics - wheel&pedal input, FFB, are one thing, and the physics engine within the game engine is another.

I for one don't know what you mean with "iRacing IS much more advanced when it comes to braking physics" - much more advanced than you had thought? Much more advanced than some other sim?

Could it be that the sensitvity of the brakes is dependant on the pedal/hardware? So by using a stiffer pedal the linearity setting becomes more effective (less of an on/off brake pedal) and therefore it can sort this out maybe, because I've heard most real race cars' brake pedals take lots of pressure to lock up...

The above is quite interesting, imo.

Some time ago there was right here an interesting thread about hardware and how people experience sims, in particular iRacing. If one has a problem (wheels&pedals oversensitivity, for instance) that will obviously affect how one experiences it.

In regards to braking, a stiffer pedal will eliminate the little jitters from muscle control. Probably a good idea. However, as someone said above, iRacing allows the user to configure braking, so maybe "playing" around with this should yield some results?

[AllanGP]

I haven't run GTR2 more or less since joining iRacing but at the time I didn't think OMG the braking is much better here than GTR2.

I really don't think you will have issues with braking in iRacing.

One thing I did think OMG comparing iRacing to GTR2 was whereas in GTR2 set up "clicks" often meant nothing, you had to do two or three "clicks" to feel changes, in iRacing one "click" you could feel straight away in set up, that was a real eye opener.

[Tony74]

Originally Posted by pro bono1984

Could it be that the sensitvity of the brakes is dependant on the pedal/hardware? So by using a stiffer pedal the linearity setting becomes more effective (less of an on/off brake pedal) and therefore it can sort this out maybe, because I've heard most real race cars' brake pedals take lots of pressure to lock up...

I've modded my G27 brake pedal (equivalent to NIXIM mod). This did make the Corvette brakes slightly better, but they're still too sensitive. However, the Riley brakes are much better so it isn't a hardware thing.

Originally Posted by pro bono1984

I try to be open to criticism and never be a fanboy of anything.
So could you elaborate on the flaws a little?
Is it serious enough to prevent a new user from enjoying it in your opinion?

You sound like a current member of iRacing !
The flaws - well, the main one for me (in terms of physics) is the inability to save slides by countersteering (you'll need to un-learn RL driving technique), and the over-effectiveness of stomping on the brakes & throttle (which shouldn't totally straighten the car to point in the original direction of travel). This will cause regular players to develop really unrealistic habits. This is mainly a problem if you plan on doing any RL motorsport.
Regarding enjoyment - depends how you'll feel in 6 months after spending £100+ on content just to run a full 12 week season when Assetto Corsa comes along with superior physics & equivalent tracks + better cars (eg BMW/Lotus/KTM X-Bow/Ferrari compared to all the heavy American muscle cars with terrible handling) yet costs less than a 1 year membership subscription for iRacing.
You should see the complaints about the physics from members on the forum who used to be major iRacing fanboys.
However, there's still the possibility that iRacing will fix these issues - especially as the competition starts to threaten their current monopoly.

[AllanGP]

Originally Posted by Tony74

when Assetto Corsa comes along with superior physics & equivalent tracks + better cars (eg BMW/Lotus/KTM X-Bow/Ferrari

I will be interested to see that.

[darock]

There are so many cars in iRacing it's amazing anyone feels they know how all the car's brakes feel. I doubt there are professional drivers who've driven half those cars in real life. There is even a good reason that would be a huge problem. Most road drivers in real life have no opportunity and make no effort to ever sit down in all the oval cars being raced. Most oval drivers never have the opportunity to run MX5s thru Indy Cars.

As for us...

Even the guys who own all the iRacing cars aren't going to race all of them enough to really know and understand more than a few. Look at their history and check out their record lap times to prove or disprove that.

I got no problem with iRacing's brakes in the cars I race being perfectly realisting or not. If you've ever worked with brakes in a real race car in the real world, you know how much you can change the feel with different pads and valving. You'll also know how differently brakes will deal with different tracks. In NASCAR the teams also run different brake setups in the same car depending on the track, so the same car should brake differently. After a fair amount of experience with a number of the oval cars there is no doubt that isn't simulated.

If the brakes do or do lock up that's another poor indication of realism. The same brakes do or do not feel the same at different tracks on different surfaces at different times.

So don't get too locked up on how realistic they feel or not. Brakes are extremely variable in the real world. They often change during the races. Be happy that doesn't happen in iRacing because we don't have g-forces to realize our iRacing brakes are fading. It'd be a kettle of fish (mostly dead ones) if they were even that realistic.

[Hotsocks]

This is an odd conversation. Most of the fastest iRacers aren't using load cells. And one of Teamredline said he didn't get on with it and reverted back. They possibly aid consistency for some. Would definitely make H&T easier but most don't do it, and anyway it can still be done with a bog standard pot pedal + Nixim to help a bit. BTW, pots have springs. Springs are governed by: F=kx. (where K is spring constant , x is deflection). Thus, deflection is proportional to force applied. It just moves more and has less force for full output.

In a RL aero car, you wouldn't lockup at high speed (initial braking). In F1 it wouldn't be humanly possible to push hard enough. Only with losing speed and downforce and where brakes become more effective than tires do you bleed off the brakes (threshold braking). This is the same in every sim I've used. In fact, you're more likely to snap lose in GTL by overbraking and not H&T'ing properly than iRacing which doesn't seem to care much about rev matching. Like Greger Hutto, I prefer to keep the default brake curve for Pot btw. Seriously, i'm only ever a few tenths of the fastest in the Skip with a G25+Nixim.

I'd suggest iRacers just have more money to spend on kit, that's all.

Allan is correct that if competitive online racing is most important to someone, then barring any leagues that satisfy you, iRacing is the place to be. However, iRacing is expensive compared to other sims. And in view of the many deficiencies and weaknesses, I really don't want to give them any more money and continue to punish them (and myself) by not buying content (tracks basically) I'd like, even though I can afford it. Seriously considering not taking up the 2 year for 1 offer, and waiting for AC.

NetKarPro and rF2 are much more immersive and fun just to drive imo. iRacing always feels like a computer game to me - synthetic, sterile and lacking a feeling of 'being there' realism. The look and sound is sanitised for want of a better word. I never get that "tingle" driving iRacing cars. I think of it as a super competitive and immersive video game but feeling nothing much to do with real driving. And I have no confidence in the realism of iRacing physics after all the changes to handling and screw ups e.g. it now transpires that the 'tested by real drivers' V8 super car is being driven by most of the fastest drivers with completely unrealistic caster angles that shouldn't work (don't in RL) if the physics was right. I don't trust the NTM at all. It's had too many weird behaviours cropping up. ...sorry I've gone off on my rant again.

Todd Wasson, who's advised Niels and knows Doug Milliken says that the turning into slides phenomenon is a symptom of the standard sim error of tire curves dropping off after the peak slip angle. In effect straightening up the wheel initially increases grip (lateral force) at the front end making things worse during countersteering. He says all these tire curves you see on the net with it dropping off after peak are bollocks and that Milliken agrees.

BTW, does anyone know how to get my AA working properly in NetKarPro? (Nvidia) I've tried every combo of settings I can think of.

[pro bono1984]

I'm sorry my English isn't very good.

So Mr. Chronus is right that GTR2 is not unrealistic.
And I like GTR2 and that's the only sim game I play.
I'm with you on the good base physics engine!

To be honest, however, I thought the braking in iRacing seems to be somewhat better if in fact all the above is true. Maybe better isn't the right word - my English fails me (as always).

Braking in sim racing is rather different from the real life braking, because brake pressure just cannot be translated into pedal travel very well.
Also, some sim racers seem to think there is a 100% pressure point (the end of pedal throw) in real life when there isn't anything like that in RL.

My understanding is that if your braking doesn't lock up the brakes, you can progressively brake harder (more pressure) for a fast laptime, because there is no maximum pressure in real life - "the strength of your leg is the limit" unless you can rupture the brake hose or something like that.

So first you have to learn to lock the brakes as quickly as possible.
At least that's what they teach in racing schools from what I understand so far.

And in GTR2, there is the default 100% pressure setting, which is of course non-existent in real life.
Whereas, most of the iRacing cars have no pressure settings? so that seems a bold move, since some may develop oversensitive braking issues because of that. That's all: a bold move.

Actually, I've found that there's this Japanese guy with a soft pedal and he is having a very hard time in the iracing's star mazda because he is used to sim games where you can brake "to the plastic" (100%?) most of the time. He in fact wrote he didn't like iracing because of that.

Also many people seem to complain that the brakes in iracing are too strong or something.
Just like many people did about the brakes of Mr. Niels Heusinkveld's historx V1.0? cars...

That being said, however, I have to say I like GTR2 the best because I can just customise it!
Also because of this point!

Originally Posted by Chronus

Another thing to consider is that the pedal input (whether throttle, clutch or brake) and its treatment does not say anything in particular about its physics - wheel&pedal input, FFB, are one thing, and the physics engine within the game engine is another.

Recently I've been doing some research and found out all this and about the importance of the threshold braking in real life motorsports.
http://www.nogripracing.com/forum/sh...&postcount=120
http://www.nogripracing.com/forum/sh...&postcount=123

So I don't know about F1 and I doubt there's any normal person outside F1 who has actual technical info on the brake pads and the tyre slip curves and stuff, because you can't access that kind of "sensitive" info if you're outside the contract (that's what I read).

But what puzzles me is that if you couldn't in fact lock the brakes of an aero car, racers would definitely have bodybuilder legs by now to be able to brake with over 1,000 lb/500kg pressure (yes, bodybuilders can do that), since more pressure or by most sims standard say 200% braking should lead to less braking distance...

That is, racers are very competitive so I think they would do almost anything to become fast. Therefore, it follows that they'd develop bodybuilder like leg muscles or anything like that even if it means say one tenth faster in few corners in a qualifying session, for there is no full pressure in real life. I know I would do a lot of leg presses because it'd take less effort to brake with that kind of pressure.
So maybe the HPD's downforce is insignificant and therefore not an aero car?

I'm not sure whether the HPD qualifies as an aero car (looks pretty fast though) although I understand F1 cars are, but still not sure about Formula Nippon or SGT or FJ like Formula cars or what amount of downforce the aero car should generate for the qualification.
I do not think this kind of discussion leads to anywhere unless you're involved in a racing team like Mr. Heusinkveld. Of course, it's essential that one needs to have learned to properly brake in a racing school.

Anyway, if in fact you can lock up the HPD's brakes at high speeds in iRacing on the high pressure setting?, in my opinion, iRacing is "reasonably" decent and realistic.
I'm not looking to "sim drive" fast cars though.

The needed pressure for most race cars would be something like 80kg, so a lot more than most production cars' 40kg (roughly) and I've read that most people are unable to lock up even production cars' brakes because they are not used to registering that much pressure at once.

My attitude towards sim games is that they are still just video games. So pretty lenient.
That's not to say, however, games like Test Drive Unlimited (which I liked a lot) are in the same category as iracing? or GTR2.

So I'm not too concerned, but in the mean time, I don't like some sim cars like the default production car from my rFactor demo - it makes a brake hiss sound but no tyre screeching even when absolutely piling on the brakes, so that's kind of extreme for a car that's meant to race.

All this may sound like a Zen koan in English, but I believe everything has degrees of truth in it and if it's too serious I'm not sure it's that good.

I understand it is confusing when it comes to the braking in motorsports because they used to believe braking in a straight line is always faster or something like that.
And a lot of racers say kick the brake pedal but some hard braking looks progressive and not exactly a kick, so like darock says, it's true "brakes are variable" to some degree (very nice way of putting it).

However, the important point to stress here is that a great many sim cars are like that rFactor car regardless of downforce, so this may be contributing to the idea that race cars brakes won't lock up.
I can think of many sim cars with some or even no downforce but all of them have the same no good brakes.
Again this to me, is not that good but if it's moddable, the problem solved!

As for the sliding behaviour, if it's THAT serious, I may not like it, but I think it's ok for me.

The biggest question for me is, I'm pretty much satisfied with GTR2 with my customisable brake pressure setting, so would I like to go into the waves of those competitive/aggressive people and race? Probably not at the moment maybe....

Thank you guys!
Sorry about my English.

[Chronus]

Originally Posted by Hotsocks

Todd Wasson, who's advised Niels and knows Doug Milliken says that the turning into slides phenomenon is a symptom of the standard sim error of tire curves dropping off after the peak slip angle. In effect straightening up the wheel initially increases grip (lateral force) at the front end making things worse during countersteering. He says all these tire curves you see on the net with it dropping off after peak are bollocks and that Milliken agrees.

Not exactly.

In both lateral force vs slip angle and tractive force vs slip ratio plots analysis shows decrease in lateral force and tractice force past the peak slip angle/ratio. This comes out of measured data from RL tires.

Reports from the National Transportation Board and Minnesota's own Department of Transportation show plots of normalized traction forces vs slip ratios, from measurements effected on a variety of tires (different brands, different constructions). Again, noticeable decreases past the peak.

Easy to understand why. On dry asphalt the peak value of the coefficient of friction is 7% to 17% higher than the sliding value of the coefficient of friction.

From the Millikens:

If the lateral force is increased, the slip angle will increase, the tire will be distorted further, and the onset of sliding at the rear of the print will move forward. The process is progressive. When the tire has enough applied lateral force that most of the print is sliding, it is said to have "broken away" and the lateral force is determined by the coefficient of friction.

The peak of the curve may remain at a constant value or fall off slowly as indicated. In dry conditions, race tires generally reach their peak lateral force at slip angles in the vicinity of3°-7°. On a wet surface the peak will in general be lower, and the fall-off in lateral force after the peak will be more rapid.

Introducing braking (tractive) efforts will further reduce cornering forces past the peak.

From Mechanics of Pneumatic Tires:

It is noted that for a given slip angle, the cornering force is reduced as a tractive (or braking) force is applied to the tire. This is consistent with the trends of the measured data shown

Furthermore, we have to look at Aligning Moment and Pneumatic Trail.

From Mechanics of Pneumatic Tires:

When the tire is moving at a uniform speed in the direction of OA, the side force Fs applied at the wheel center and the cornering force Fy developed in the ground plane are usually not collinear, as shown in Fig. 1.22. At small slip angles, the cornering force in the ground plane is normally behind the applied side force, giving rise to a torque (or couple), which tends to align the wheel plane with the direction of motion. This torque is called the aligning or self-aligning torque, and is one of the primary restoring moments which help the steered tire return to the original position after negotiating a turn.

The distance tp between the side force and the cornering force is called the pneumatic trail, and the product of the cornering force and the pneumatic trail determines the self-aligning torque.

The relationships between the slip angle and the cornering force of various
types of tire under a variety of operating conditions have been investigated
extensively.

Plots of aligning torque vs slip angle show dramatic decreases past a certain peak value of slip angle.

...

Conclusion is easy to draw. The slip curves "dropping off after peak are" definitely not "bollocks". Measured data and different types of simulation models show this.

Now, some devs and modders seem to think that the decrease of lateral and tractive forces past the peak is hugely dramatic, when it is not. The decrease is there, but is not as marked as the "hard is realistic" crowd would want us to believe.

[darock]

More than one authority has illustrated tire traction with graphs that show the tire traction versus slip angle and every one shows the same thing.

The slip angle at which maximum traction occurs is a range that is almost constant for a significant period. If the authority is discussing racing and race drivers they almost always suggest that the best drivers somehow identify when their tires are in that slip angle range and capitalize on it.

The first graph I ever saw showed up when radials showed up in oval racing. It compared bias ply slip angles to radial ply angles. The author was attempting to show why the best drivers were still the best and why the the back markers were finishing even farther back.

Unfortunately, what the best drivers in real life were feeling appears to be missing in simulations that don't include g-forces.

[Hotsocks]

First off take it up with Todd Wasson. But I'll point out that some of your quotes involve traction forces and someone here asked me privately for some references to Todds comments which I provided and actually edited out a bit from one where he made the point he was talking purely about lateral force and not getting into tractive, which would complicate things. To be honest I don't really see the relevance of some of your generic quotes about tire behaviour on this.

BTW, DK actually said in a video at one point that the coefficient of friction is pretty much a meaningless concept in this area!

Secondly, from reading what Todd and others have said about 'data', one has to be extremely suspicious about claims of real data for over-the-limit behaviour. It apparently doesn't take long to destroy a tire on a test rig in this region. And you couldn't even usefully test an F1 tire on such a rig e.g. Calspan as it couldn't generate the forces. Does the "National Transportation board" et al really spend time on tire rigs testing tires to destruction in regions that only racing drivers normally inhabit? Such data there is, is held by manufacturers and race teams and they don't share it. Most of it on the net I think Todd is saying has no credibility when showing significant drop off. Apart from anything, if you test the same tire on the same rig, the same day, the experimental error/noise drowns out the real drop-off such as exists. Look, I'm referencing Todd saying no fall off after the limit, but I think he's acknowledged that there's some, but nothing of the order of the curves that are normally referred to by everyone including Carroll Shelby's book that Todd showed Milliken in person and he concurred it was nonsense.

To be honest, it would surprise me if there wasn't some fall off. But the best thing to do is speak to Todd either at LFS forum (which he reckons is the only sim, certainly at the time of writing, that had the curves about right) or the iRacing forum. Personally, I'd guess LFS is a little too tolerant over the limit. and the truth is somewhere in the NetkarPro/rF2 ballpark with iRacing being too slippery there.

I might be interested in talking to you about modding btw. Never done it myself. But at some point if I get time I might have a dabble/experiment with tire physics.

[Hotsocks]

Originally Posted by pro bono1984

But what puzzles me is that if you couldn't in fact lock the brakes of an aero car, racers would definitely have bodybuilder legs by now to be able to brake with over 1,000 lb/500kg pressure (yes, bodybuilders can do that), since more pressure or by most sims standard say 200% braking should lead to less braking distance...

To be clear, it's just at the very start of braking at high speed that this is true. But the deceleration is very fast with the brakes being very efficient, so that the F1 drivers then of course have to decrease the pressure (threshold brake). It's only for a moment that the high downforce exists. Don't know why I mentioned it. There is actually a limit even on an F1 car to how fast you could usefully apply the brakes. But the longer it takes for the suspension to compress on a given car, the longer one should take to apply full pressure. Too soon and there's not enough 'weight' over the front tires and they'd lock. In an aero car you could be talking a couple of 10ths of a second apparently.

[Chronus]

Originally Posted by Hotsocks

First off take it up with Todd Wasson.

Nah, no need to.

I do my own research and math. I don't quote someone who quotes someone or says he talked to someone.

You are simply wrong - in many ways.

I quoted from SAE and US transportation authorities.

You, on the other hand, make a reference to someone else's comments.

Nothing more to it, really.

Do your research instead of making "suspicious" references to what somebody else said.


---

@darock,

there is a peak. The slip angle/ratio where maximum forces (lateral or longitudinal) occurs is a peak - before it, forces are building up, afterwards, it falls off very slowly (or, for some tires, remains constant for a few degrees before eventually falling off). On the wet, this fall off happens more sharply.

The problem with commercial racing simulations is that, for reasons other than simple math, some models make the dropoff very pronounced and almost immediate, when in fact the dropoff is slow. Ian Bell often reminded people of this (irrespective of his motivation for doing so), but it seemed if fell on deaf hears.

With the "harder is realistic" myth firmly installed in the minds of a lot of simracers, it is easy to "inject" this artificial and fast dropoff into tire models.

However...DK has seemingly committed to a full physical modelling, and the issues he faces are somewhat different.

My 2 cents.

[Kalifen]

Originally Posted by pro bono1984

And in GTR2, there is the default 100% pressure setting, which is of course non-existent in real life.
Whereas, most of the iRacing cars have no pressure settings? so that seems a bold move, since some may develop oversensitive braking issues because of that. That's all: a bold move.

Well, as long as you make sure that 100% pedal travel is always "useless" (=locking brakes), then it's not necessarity that bold a move, is it?
(can't speak for all cars, but those I drive I can easily lock up)

Actually, I've found that there's this Japanese guy with a soft pedal and he is having a very hard time in the iracing's star mazda because he is used to sim games where you can brake "to the plastic" (100%?) most of the time. He in fact wrote he didn't like iracing because of that.

While this is why I dumped my Logitech DFP pedals (equal to DFGT, I believe) a long time before I even turned to iRacing. Even in other sims I played it was an advantage to modulate the brake and be sensitive. Tell him to get better pedals... I'm actually serious, you can't get anywhere near a realistic experience with soft pedals. You *can* learn to go fast, but the muscle use will be very different from a real driver.

I'm not sure whether the HPD qualifies as an aero car (looks pretty fast though)
...
Anyway, if in fact you can lock up the HPD's brakes at high speeds in iRacing on the high pressure setting?, in my opinion, iRacing is "reasonably" decent and realistic.

They have said multiple times that the HPD is the car that produces the highest amount of downforce in the service, so there you go They did turn down the effiiency a bit a while ago, but I guess it still holds true.

My memory tells me that back when I was driving the HPD, I could lock up the brakes at any time. There were rather huge differences between the brake pressure settings, though, I believe it was possible to apply full pressure with "Low" without locking up, but I never used that setting other than quick tests out of curiousity.

[Hotsocks]

Originally Posted by Chronus

Do your research instead of making "suspicious" references to what somebody else said.

Charming.

For anyone else interested in Todd's comment where he says most tires have no drop-off, "none zero,nada":

http://members.iracing.com/jforum/po...0/1838981.page

This is me:

Think about it: authors quote tire curves everywhere, showing neat little lines of drop-off. But the actual data obviously isn't a line, it's a scatter of points and they're different ever time they test it, even the same tire same day. And where did they get it from? They didn't spend thousands of dollars a day testing tires, let alone to destruction. Race teams have data. Todd's point is a lot of these curves aren't real and certainly not reliable.

[Chronus]

Originally Posted by Hotsocks

For anyone else interested in Todd's comment where he says most tires have no drop-off, "none zero,nada":

For anyone interested in someone's comments...

For anyone interested in what a racer and physicist says, here's food for thought from Dr. Beckman:

The greater the grip angle, the larger the cornering force becomes, up to a point. After this point, greater grip angle delivers less force. This point is analogous to the idealized adhesive limit mentioned earlier in this series. Thus, a real tyre behaves qualitatively like an ideal tyre, which grips until the adhesive limit is exceeded and then slides. A real tyre, however, grips gradually better as cornering force increases, and then grips gradually worse as the limit is exceeded.

Curve interpretations, noise (a lot, no doubt) in the data collected, how difficult it is to obtain data, how secretive tire companies are - all this has little bearing on what the bottom line is: "A real tyre, however, grips gradually better as cornering force increases, and then grips gradually worse as the limit is exceeded."

This "grips gradually worse as the limit is exceeded" is exactly what, regardless of model, the slip curve modelling tries to achieve (the infamous dropoff you say is "bollocks"), and it is what we are talking about.

All the SAE/USDT/Dunlop/Goodyear/Continental data available or provided by racing teams points to that.

What Todd W. says and what you are doing are entirely different things. He researches, has been working in this and has his opinion on all this; on the other hand, your opinion is....his opinion, whatever it may be. Odd...

I can give you a list of links or publications for you to read and think about. That is the only way to actually understand this subject (or understand that there is a lot yet to be understood) and then make up your mind about it. Sure, it is complex, but I'd bet most people here would have no problem in going through all the info and data, understand it and apply it to the current crop of simulations.

[darock]

Originally Posted by Chronus

@darock,

there is a peak. The slip angle/ratio where maximum forces (lateral or longitudinal) occurs is a peak - before it, forces are building up, afterwards, it falls off very slowly (or, for some tires, remains constant for a few degrees before eventually falling off). On the wet, this fall off happens more sharply.

Having seen the charts, I would suggest you are right but seem to have missed my point.

The charts are clear what they show. Traction versus slip angle. The information they provide is how the traction varies in relation to the angle the tire is experiencing. The data is taken from the test machinery every manufacturer (that tests their products) uses. It's not computed with slide rules, it's measured. And what it showed was that the traction builds quickly as the slip angle increases until it approaches an angle where it begins to level off. There is basically a somewhat flat curve that starts before the slip angle that gives max traction and continues beyond somewhat. The curve then plumets.

With bias ply tires the charts show that they sustain significantly greater slip angles and the flat curve is appreciably wider than radial tires produce. In other words, the bias ply tires could be 'hung out' more and the area of best traction covered a wider range of slip angle. That was proved the first time radials were raced against bias ply tires and has been proven every time since.

What that leads to is the universally accepted belief that it takes more driving skill to drive radials fast than to drive bias tires fast. Which explained the observation hundreds of NASCAR fans and media made when they saw what happened during that changeover. The good drivers appeared to outrun the mediocre ones even farther. The mediocre ones could keep up better on bias. They didn't have the refined touch to keep up as closely on radials. The tire testing tools explained what formulas and slide rules didn't.

But another thing to get out of this is that it didn't require the tire companies work their slide rules to tell how their tires perform. They have direct reading tools they use every day that quantify traction and when it occurs and how.

[Hotsocks]

Originally Posted by Chronus

What Todd W. says and what you are doing are entirely different things.

What ARE you going on about? I'm not doing anything. I just quoted Todd saying - and he's said it quite a lot in various places - that real tires don't drop off much, if at all over the limit, that that's where all the sims other than LFS get it wrong, and that the ability to save slides by turning into them is a sure sign of it. Although thinking about it, you can actually do that in LFS too apparently - think there was a thread about it. Anyway, I certainly haven't the time or inclination as most people haven't to research tire data!

[darock]

Originally Posted by Hotsocks

What ARE you going on about? I'm not doing anything. I just quoted Todd saying - and he's said it quite a lot in various places - that real tires don't drop off much, if at all over the limit, that that's where all the sims other than LFS get it wrong, and that the ability to save slides by turning into them is a sure sign of it. Although thinking about it, you can actually do that in LFS too apparently - think there was a thread about it. Anyway, I certainly haven't the time or inclination as most people haven't to research tire data!

Since real tires don't drop off much when over the limit, then spinning out happens why?

The sudden loss of traction that puts cars into the wall doesn't happen?

[darock]

In fact real tires don't gain much nor drop off much around their optimum slip angle. There is a plateau of traction just before and just after.

The really good drivers can feel the beginning of drop off just after the optimum angle and appear able to hold the car there.

The not so good drivers appear to drive on the safe side of the curve. The ones who spin less than the not so good drivers who haven't noticed the plateau that is.

[Chronus]

Although thinking about it, you can actually do that in LFS too apparently - think there was a thread about it. Anyway, I certainly haven't the time or inclination as most people haven't to research tire data!

Hmmm...

How you got from iRacing brakes to slip curves being "bollocks" in sims is strange. Hence my (polite) response to you. From then on, you pulled some tricks up your sleeve.

Since you seem familiar with Todd, ask him about ways of dealing with the noise/dispersed plots, ask him about Kalman filters and how researchers can use this to obtain higher accuracy from noisy input data.

That is the point you seem to be oblivious to: physics and data say that a "real tyre, however, grips gradually better as cornering force increases, and then grips gradually worse as the limit is exceeded."

The way we go about representing lateral force/longitudinal force/aligning moment vs slip angle/ratio representation, regardless of noise and difficulties in accessing data, is another matter.

Now, if you don't have the inclination or time to research this, why then make some comment about this subject without giving it substance other than mentioning "ah, that is what Mr. Such-and-Such is saying"?

At least, could you go about it differently?

In fact real tires don't gain much nor drop off much around their optimum slip angle. There is a plateau of traction just before and just after.

The really good drivers can feel the beginning of drop off just after the optimum angle and appear able to hold the car there.

There is a plateau, fully agree (or sort of). About all the data I have dealt with points to that.

But the shape of curve is not linear. There is a region of linearity, but there is clearly a gain and a dropoff as one increases slip angle. Question has always been, how acute is this dropoff? It seems the dropoff is gradual and slow.

That should be key in developing simracing tires.

The not so good drivers appear to drive on the safe side of the curve. The ones who spin less than the not so good drivers who haven't noticed the plateau that is.

This, obviously, is my personal opinion: I suspect that the current model (NTM) is still having trouble providing iracers with the necessary feedback for drivers to realize, as you point out, where is the "safe side of the curve".

EDIT:

which makes me think of the FFB in iRacing.

Is its FFB helpful enough in help determine the limits of traction? I haven't driven a single second in the last 4 months or so, and before that never really used FFB much (thus saving my G27 a bit more), so I honestly don't know how it is.

I remember several discussions about FFB and Pneumatic Trail, back in the days of early exploration of the ISI engine.

In RL, some researchers are using Pneumatic Trail (or at least, the information related to PT in steering torque) to help determine lateral tire force.

I obviously don't know iRacing's code or model, but I wonder if this is being used to the extent that it can be used, or is being fudged?

[Hotsocks]

Originally Posted by Chronus

Hmmm...

How you got from iRacing brakes to slip curves being "bollocks" in sims is strange. Hence my (polite) response to you. From then on, you pulled some tricks up your sleeve.

Since you seem familiar with Todd, ask him about ways of dealing with the noise/dispersed plots, ask him about Kalman filters and how researchers can use this to obtain higher accuracy from noisy input data.

That is the point you seem to be oblivious to: physics and data say that a "real tyre, however, grips gradually better as cornering force increases, and then grips gradually worse as the limit is exceeded."

The way we go about representing lateral force/longitudinal force/aligning moment vs slip angle/ratio representation, regardless of noise and difficulties in accessing data, is another matter.

Now, if you don't have the inclination or time to research this, why then make some comment about this subject without giving it substance other than mentioning "ah, that is what Mr. Such-and-Such is saying"?

At least, could you go about it differently?

Well, FWIW, and since I'm only watching F1, I brought up lateral force curves because someone earlier in the thread mentioned a problem with saving slides in iRacing. I quoted Todd (who i don't know personally), but is arguably the most respected iRacing member on tire physics, whose had lengthy debates with Eric Hudec on tire numbers, been involved with sims a long time, written his own, and personally knows Doug Milliken. Perfectly reasonable comment to any reasonable person. Todd's actually referred to some curves you see showing significant drop-off quoted on forums and even manufacturer's data floating around as barely more than artist's impressions. Bollocks seems apt.

What tricks did I pull out of my sleeve Chronus?

As for dorock, on spinning out. It's a valid point and I've wondered about Todd's comments. But then you're dealing with rotational inertia during turn- in (there could be angular acceleration too) with a levelling off of the lateral force which was increasing. Plus, of course, once you get too far round, the front tires can no longer roll beyond full lock.

[Scalage]

Ok, this might be a little out of the blue: I know Todd Wasson. He is a physics developer for an RC sim called VRC Pro, of which I am a moderator (Marco Hooghuis).
I just asked him what the fuss was about. Let's see what he says.

[Chronus]

Originally Posted by Hotsocks

Bollocks seems apt.

Fine. I'd rather look into things myself before qualifying anything as "bollocks", but everyone is different. You read something somewhere and off you go with "bollocks".

Fine.

What tricks did I pull out of my sleeve Chronus?

Look at the phrasing you used, your references. In any serious, interesting conversation (which I supposed you were engaged on, if not then my mistake), people provide more substance than qualifying other people's post as generic when you yourself provide vague mentions to someone else's comments. But, again, everyone is different, and that was your way of addressing what I posted.

I quoted Todd (who i don't know personally), but is arguably the most respected iRacing member on tire physics, whose had lengthy debates with Eric Hudec on tire numbers, been involved with sims a long time, written his own, and personally knows Doug Milliken.

Todd is a respected individual.

But then, so is Eugene C., Ruud van Gaal, or Doug Arnao. Since you're basing your opinion on what someone says and not on books/papers/data, why not ask these individuals what they think? You may be surprised.

As for dorock, on spinning out. [...] But then you're dealing with rotational inertia during turn- in (there could be angular acceleration too) with a levelling off of the lateral force which was increasing. Plus, of course, once you get too far round, the front tires can no longer roll beyond full lock.

Hmmm...

[Chronus]

Originally Posted by darock

Having seen the charts, I would suggest you are right but seem to have missed my point.

The charts are clear what they show. Traction versus slip angle. The information they provide is how the traction varies in relation to the angle the tire is experiencing. The data is taken from the test machinery every manufacturer (that tests their products) uses. It's not computed with slide rules, it's measured. And what it showed was that the traction builds quickly as the slip angle increases until it approaches an angle where it begins to level off. There is basically a somewhat flat curve that starts before the slip angle that gives max traction and continues beyond somewhat. The curve then plumets.

I understand.

With bias ply tires the charts show that they sustain significantly greater slip angles and the flat curve is appreciably wider than radial tires produce. In other words, the bias ply tires could be 'hung out' more and the area of best traction covered a wider range of slip angle. That was proved the first time radials were raced against bias ply tires and has been proven every time since.

True indeed.

What that leads to is the universally accepted belief that it takes more driving skill to drive radials fast than to drive bias tires fast. Which explained the observation hundreds of NASCAR fans and media made when they saw what happened during that changeover. The good drivers appeared to outrun the mediocre ones even farther. The mediocre ones could keep up better on bias. They didn't have the refined touch to keep up as closely on radials.

I see what you mean and fully agree.

The tire testing tools explained what formulas and slide rules didn't.
But another thing to get out of this is that it didn't require the tire companies work their slide rules to tell how their tires perform. They have direct reading tools they use every day that quantify traction and when it occurs and how.

Ok.

From the readings/raw data output from test rigs or road tests it is possible to extract data to either feed existing tire models or build new ones. We have to deal with both noise and physical limitations (sensor readings, conditions for testing, etc), true, but it is possible to achieve an important degree of accuracy.

I'd say, as always, every theory (model) can be and must be subjected to experimentation before we perfect it. Given enough time, "formulas and slide rules" will provide clear explanations on what is happening with a certain tire.

[MickeyMouse]

I think one issue when looking at real slip curve data is that temperature can not be extracted from the results, but it must be before it can be used in a sim. In other words, the reason a real test shows a drop off after a peak isn't because of the increased slip angle, but rather the increased slip angle leads to increased temperatures which leads to decreased grip. In a sim, if one uses a drop off curve (take F1C for example, that had a 60% drop off to 90deg), and then adds temperature on top of that, the drop off effect becomes unrealistically strong. In a sim, the slip angle / grip coefficient curve should not drop off, as it does not in real life when temperature is extracted. When temperature effects are added to the equation while simulating, there will actually be some amount of drop off in the end.

[MickeyMouse]

Originally Posted by darock

Since real tires don't drop off much when over the limit, then spinning out happens why?

The sudden loss of traction that puts cars into the wall doesn't happen?

In theory, the range of the peak has the most influence on how 'forgiving' a tire is. By range, I mean the distance between the fall off of the derivative of the slip curve and when it becomes 0. This range is significantly longer in a treaded tire versus a slick, for example. Some have postulated that a quickly peaking tire can feel like a sudden grip fall off to the driver, giving them incorrect assumptions on what the tire is actually doing (leading to Shelby-like graphs).

[pro bono1984]

OMG! I thought I'd started a braking thread but wow!

Originally Posted by Kalifen

They have said multiple times that the HPD is the car that produces the highest amount of downforce in the service, so there you go

Thank you, thank you, Kalifen! I've been looking for this kind of info all over the net!

Originally Posted by Kalifen

Well, as long as you make sure that 100% pedal travel is always "useless" (=locking brakes), then it's not necessarity that bold a move, is it?

Yes, I know! It makes a lot of sense if you put it that way! but in GTR2, you can brake 100% most of the time. The same goes for most of the slow cars and road cars, pretty much irrespective of downforce, so we need to mod!

Originally Posted by Kalifen

While this is why I dumped my Logitech DFP pedals (equal to DFGT, I believe) a long time before I even turned to iRacing. ... Tell him to get better pedals... I'm actually serious, you can't get anywhere near a realistic experience with soft pedals.

Lol
Unfortunately I don't know the guy who's having a dreadful time with iRacing, although I might have raced with him online.

You know he was used to GTR2. So much so that he seemed pretty confident going into iRacing because he was one of those alien people, but you know the braking is rather different so it made his soft pedal almost useless.
On his blog, he wrote he cannot brake at all well if he can't press the pedal all the way to the plastic stopper thingy.
He even said his iRacing experience is like a living hell!

Anyway, thanks a million again!! Awesome!

[Hotsocks]

Originally Posted by Chronus

But then, so is Eugene C., Ruud van Gaal, or Doug Arnao. Since you're basing your opinion on what someone says and not on books/papers/data, why not ask these individuals what they think? You may be surprised.

Is this real I ask myself...

If you weren't so busy playing the man (in both senses) you'd have noticed I've not expressed any particular definitive opinion either way. Just quoted someone whose talked with a professional tire tester (Milliken). Just like you quoted from authority in the shape of Beckman who's a physicist not even a tire engineer or tester. For the record, I was somewhat surprised by what Todd said, but I'd guess it's probably right that they don't fall of much past the peak on the basis that the changing gradient from + to zero would be enough to account for a lot of what drivers perceive. But I think there are other issues in iRacing affecting slides/snap backs etc.

I don't know if your bizarre over reactions here are because you're still miffed over what I said to you ages back about not knowing what the skip drivers were doing when you claimed they were sliding to be fast. You went off in a huff then. If it is, then grow up!

It's like a soap....

[Chronus]

Originally Posted by Hotsocks

Just quoted someone whose talked with a professional tire tester (Milliken). Just like you quoted from authority in the shape of Beckman who's a physicist not even a tire engineer or tester.[...]

You are getting more and more tedious by the hour.

I quoted or mentioned works/statements by Beckman, the Millikens, S.W. Clark, J. Katz, Han-Shue Tan and Masayoshi Tomizuka.

As you seem to be enjoying yourself with such nonsensical posts, I leave it at that.

professional tire tester (Milliken).

You don't really know who the Millikens are, do you?

Go now, go and google them. Or better yet, read their books.

[David Wright]

Originally Posted by MickeyMouse

... (leading to Shelby-like graphs).

I know you weren't the first to refer to the graphs as being from Carroll Shelby, but can I correct this please

The graphs are from Carroll Smith, and he should be treated with respect. He worked for Goodyear racing tyres in the 60s before moving on to work with Shelby as part of the Le Mans winning Ford GT programme. In terms of hands on experience with real racing cars the guy has quite some CV. So he almost certainly had access to tyre manufacturer's data. The graphs in his book may or may not be accurate, perhaps as a result of the tyre testing limitations of the day.

[Chronus]

Originally Posted by MickeyMouse

I think one issue when looking at real slip curve data is that temperature can not be extracted from the results, but it must be before it can be used in a sim. In other words, the reason a real test shows a drop off after a peak isn't because of the increased slip angle, but rather the increased slip angle leads to increased temperatures which leads to decreased grip.

Temperature, load and pressure - all of them affect lateral force, aligning torque and longitudinal force.

But the bottom line is this:

If the lateral force is increased, the slip angle will increase, the tire will be distorted further, and the onset of sliding at the rear of the print will move forward. The process is progressive. When the tire has enough applied lateral force that most of the print is sliding, it is said to have "broken away" and the lateral force is determined by the coefficient of friction.
- Race car vehicle dynamics

In the elastic part of the tire operation, almost no slipping occurs. With enough tire print distortion, a large area of the print will experience sliding.

When most of the print is sliding, we enter an area where lateral force is determined by friction.

The transition from the elastic range to "break away" (most of the print sliding) is determined by distortions, not temperature (note: we're obviously disregarding thermodynamics and what happens at a molecular level, something DK seems to have introduced in his tire model).

Tire load, pressure, temperature and even speed effects affect tire performance, but we can (noise aside) extract "slip curves" from the data and we verify the existence of a dropoff (albeit slow and gradual).

The isiMotor2 engine deals with other factors affecting tire performance, precisely load, pressure, temperature and speed effects (linearly or not). When they give the chance of "modding" tires to the end user they provide the means to determine how effective are load/pressure/temperature/speed in influencing tire behaviour.

In other words, via the dropoff function and loadSens/OptimumPressure/HeatBasePeak/Heating/Temperatures/GripTempPress/SpeedEffects, we can effectively model tire behaviour (to a more or lesser degree of accuracy, granted) - its grip changes, its lateral forces vs slip angles and ratios.

People may or may not like the isiMotor2 engine, but I for one believe it provides us with enough flexibility and accuracy to properly mod/design tires for racing sims based on it.

In a sim, if one uses a drop off curve (take F1C for example, that had a 60% drop off to 90deg), and then adds temperature on top of that, the drop off effect becomes unrealistically strong.

No.

It depends on the values fed to the physics engine, in other words, it depends on tire model calibration.

In a sim, the slip angle / grip coefficient curve should not drop off, as it does not in real life when temperature is extracted. When temperature effects are added to the equation while simulating, there will actually be some amount of drop off in the end.

In the real world, lateral forces decrease past a certain range of slip angles. This ensues from the distortions in the tire print.

Again, and in this can be found in other sources as well, we have to understand the following:

If the lateral force is increased, the slip angle will increase, the tire will be distorted further, and the onset of sliding at the rear of the print will move forward. The process is progressive. When the tire has enough applied lateral force that most of the print is sliding, it is said to have "broken away" and the lateral force is determined by the coefficient of friction.
- Race car vehicle dynamics

-----------------------

Originally Posted by David Wright

The graphs are from Carroll Smith, and he should be treated with respect.

Indeed.

[David Wright]

Interesting thread - both on braking in sims and slip curves.

All I would say is that as well as GTR2 being designed for "bog standard" sim brake pedals, it is also an endurance simulator. If it was too easy to lock brakes in the dry with new tyres, then driving on worn tyres or in the wet would be too difficult.

I would also point out that in real racing it is locking the "inside" wheel that is the most common issue and this is easy to do in GTR2 even in the dry.