View Full Version : Noob Setup ??'s...
21 September 06, 06:04
I've got the "BASIC" Idea of Bump, Rebound, Camber...
Bump value = force needed to move wheel up
Rebound value = force needed to move wheel down
Camber value = relationship of wheel to track (+ or - in degrees)
where do the springs come in ? are they static until the car turns, brakes, etc ?? how do they work with the bump & rebound ??
what is caster exactly ? & how does it work with Camber ?
Thanx for reading & putting up with dumb questions...:confused::
PS.. no need to post a novel, just a quick & dirty answer would be appreciated ... uhh... if this is possible...:D
22 September 06, 15:23
You can't do this properly without a novel ;)
Springs: Support the car and resist the movement of the body downwards or the wheels upwards. I.e body down might be going into a dip or braking (nose down) accelerating (tail down). Wheel up might be hitting a bump.
Too soft on the springs and the car will roll/pitch more and might hit the bump stops cornering/braking/accelerating or hitting a bump. Hitting the bump stops is a bad thing as the wheel rate goes to infinity and the tyre tends to lose it's grip with the road.
You can affect the hitting the bump-stops bit by playing with ride height too.
Damping generally; I wouldn't think of it as a forcce. Springs have a bigger part to play in that. Think of damping as the bit which affects the speed at which the wheels or car body can react to movement.
Bump Damping: This affects the speed the wheel moves when moving upwards relative to the body (or body moving down). Too soft and the car will (for example) nose dive instantly to full travel on the brakes. In real life a good sign of not enough bump damping is a car that won't take a "set" in a corner. Too much and the feels harsh and kicks off on bumps.
Rebound: The other way to above. This controls how the wheel returns to it's normal ride height. In my opinion you use rebound damping mainly to tune transient response. A good example - at the rear of a car, increasing rebound can make it unstable under braking (it takes longer for the wheel to be "realease" towards the road as the front dips). This can be desirable or not depending on what you want your car to do.
Camber value: Typically get you camber in the ballpark by looking at tyre temps - try and get the inside temp a few degrees hotter than the outside (how much is a good temp difference seems to vary with the cars/tyre width). Then use the tyre pressures to get the middle temp somewhere between the inner & outer temps. Camber creates "camber thrust" which helps a car turn also imagine pushing an eraser sideways across your desk. Hold it upright and it moves quite easily, hold it at an angle (top leaning away from the direction you are pushing) and it's harder to push. This is because the sideways force deforms the contact patch and lets it assume a better angle to the road.
Castor is the angle of the steering axis when viewed from the side (like the angle of the forks on a motorbike). Castor (in the normal sense as we have in GTL) creates directional stability (but this is NOT why it's used for tuning), it makes the steering heavier. BUT when the wheel is turned by the steering it rotates around this axis - this creates additional negative CAMBER on the outside wheel. So, is almost something for free. Although I did read a good explanation as to why too much camber can make a sliding car hard to control. It's worth trying it if you car understeers in long corners. Probably works best with cars that roll a lot.
Please don't forget the diff' probably one of the biggest influencers of a car's behaviour. Car reluctant to turn? Try less coast side lock. Car unstable on the brakes? Try more coast side lock. Car understeers under power? Try less power side lock. Car has snap oversteer under power? Also try less power side lock.
23 September 06, 06:11
First off let me say thanx for that HUGE amount of info...(Geez I bet your fingers hurt after that..)
And secondly if I may, ...
"Please don't forget the diff' probably one of the biggest influencers of a car's behaviour. Car reluctant to turn? Try less coast side lock. Car unstable on the brakes? Try more coast side lock. Car understeers under power? Try less power side lock. Car has snap oversteer under power? Also try less power side lock."
My diff settings almost never change... 30/10.. As I'm sure this has caused me troubles, I can only guess that I've been setting the suspension to compensate...
Camber & tire temps I pretty well understand , but what an excellent analogy you used with the "pushing an eraser sideways across your desk". Absolutely the best description I've ever heard...
Now to Castor...
"Castor is the angle of the steering axis when viewed from the side (like the angle of the forks on a motorbike). "
Meaning ... a zero degree setting is perpendicular to the road ?
Negative castor leans towards the rear & positve castor leans forwards ??
I see how the rotation would induce a negative camber, but am kinda lost on the actual part of the car that creates this...
Is it the spindle & it's angle to the road ??
Dampner is more shocks that springs I'm guessing ... Stability in keeping the wheel in contact with the road... or just one half of it... with rebound being the other half... Thinking of Speed instead of Force ... could this be why You'll see one wheel out of contact under braking while watching the "speed vision touring series" ?? I've noticed that the Mazda 6's will go around a corner litterally on 3 wheels...
Well, this is the quick reply box but it wasn't so quick...
thanx again for your answer & patience in your explanation...
23 September 06, 10:00
The "eraser" analogy was from a certain Carroll Smith (google to find more about this brilliant race car engineer - some of the best and most entertaining stuff you will ever read).
IMHO the diff is very important because we are rarely in steady state, neutral throttle cornering. We are braking and trying to get the cars to turn and then getting back on the power as soon as possible. So, the connection between the engine and driven wheels is a strong factor in car performance.
Definately play with diff settings. Cars like the Porsche 911, the Alp' seem to like a fair amount of coast side locking. BUT watch the tyre temps, I have noticed that the Pantera could do with strong coast side lock, but cooks it's rear tyres if there is too much.
Castor - as you describe (although I forget what the GTL menus call it). When the wheel is turned it has to pivot around the top and bottom joints. If you stick a piece of card to a pencil (edge of card running down the length like a flag). Stand the pencil upright and twist it, the card just rotates and the free edge is vertical to the ground; lean the pencil back and rotate and you will see a change in angle between the top and bottom of the card's edge. Or go to a car park and find someone who has parked the car on full lock (bigger cars like Mercedes seem to show this really well - some cars much less) - you will see the wheels at all sorts of angles.
To confuse things even more, when viewed from the front the steering pivot often tips in at the top - this is called King Pin Inclination (KPI) and affects the steering offset - but this isn't adjustable in GTL.
Damping - Your damping analogy isn't quite right as if it was only damping holding the wheel up, it would eventually return to it's correct position. This is probably something in the suspension doing this - most likely a stiff ARB, which will literally lift the inner wheel off the road. The spring is the bit that determines the basic stiffness of the car in roll, pitch, bump. I think you are asking about the "shock absorber" (badly named because the springs absorb shocks! ;)) - perhaps we should call it the damper for clarity. Without a damper, if the car was disturbed by a bump, roll, pitch or whatever the spring would compress to absorb the energy (shock absorbing!) then release that energy back returning to it's original length - BUT without damping to control it it will overshoot and extend too far and keep bouncing until it runs out of energy - meanwhile the car has probably hit another bump or is cornering or whatever and it never stops bouncing and is an uncontrollable mess.
The damper intervenes in the process. On the bump cycle it controls how fast the spring is able to compress and on the rebound cycle it controls how fast the spring can extend. Imagine a heavy wheel hitting a bump, the wheel is moved up and the spring tries to resist the movement - if the wheel is very heavy it will accelerate and gains momentum - this momentum may take the wheel clean off the road. A heavier spring will help here, but also the bump damping as it will resist the wheel's acceleration. Same idea in roll and pitch - if you hit the brakes the car tries to pitch and the body tries to gain momentum. Too soft on the springs and dampers and the nose heads for the floor and hit's the bump stops making the tyres (probably) lose grip with the road). Also the driver feels like he's in a fairground ride. A car that is underdamped and undersprung probably rolls and pitches too much and is soggy and unresponsive - a car that is oversprung and overdamped will be harsh and darty and will probably overwork it's tyres.
25 September 06, 05:08
thass what I've been doin since talking to you... & here's my observations... Again, please remember that I'm racing amateur strength oppo's, but am gonna change that soon as they're seemingly too slow in the last few days...
Increasing Castor helps in the sense of turning in is more aggressive at all speeds but if I take it too far, I tend to push the front end & loose grip accelerating out of a corner...
springs have been stiffened greatly with really good results! stability under hard braking has really improved ... (runnin Front ARB one knotch from full seems to help also) ... A slightly lower camber, with a slightly higher castor setting, along with aggressive front brake bias really allows me to wait til the last second to hit the brakes/gear down, time it to turn in under them or accel faster than them out of corners (fast or slow)...
Diff settings, changing this has been a dissaster for me... when entering slow speed corners (1st gear), the tail ALWAYS slide out... putting it back cures it... I can only guess that one rear tire with more grip coasting in causes the other 3 to lose traction with my style of driving...
Softening the front dampner & rebound to a medium setting (2/3 respectively)
seems to have helped also, tire temps look good on the front end ... And I've increased braking bias to the front quite a bit after doin a bit of reading & research... that's helped this Combo has helped with the stability during hard braking, allowing me to let off & roll or accel thru the corners...
stiffening the rear Dampner/Rebound has helped with turn in & accel off... reducing rear brake bias helped a bit too I'm sure, & during hard braking at Monza over some of the bumps, I've gained a lot of stability... which allows me to focus on the track & cars ahead, rather than wonder what My Cars gonna do til the last second...
my lap times at MonzaGP dropped 2.1 sec's & at DonningtonGP 1.7 sec's ... I firmly believe it due to the dampner/rebound/springs/castor settings we've disscussed...
Thanx again Roger for your replys & your patient explanations...
If you'd like I can upload the setup to you... that why you can try it & tweak it & give it back... you might like it, but will prolly hate it, but we can learn something from each other maybe... & thass what matters most... :D
take care & thanx again...
25 September 06, 08:01
I think the most valuable lesson is the one you have taken on board. Start thinking about the setups and don't be afraid to try ideas out. I don't believe there is a magic fix for anything - so often people complain of (say) understeer and the stock answer is either soften the front ARB or stiffen the rear. It's not as simple as that - especially with these cars which may have fundamental "problems" that need work-arounds to fix (i.e. they are not purpose built single seaters).
Glad you have found time with the setups.
One little (not real world specific) tip.........try and learn to drive with high steering lock settings (P_G_ started me on this path); I typically run 29/30degs now and am faster, also more able to deal with "moments" during a race.
25 September 06, 18:31
"One little (not real world specific) tip.........try and learn to drive with high steering lock settings (P_G_ started me on this path); I typically run 29/30degs now and am faster, also more able to deal with "moments" during a race."
Now this is weird, I've just last week edited the PLR file to cancel the steering help at low speeds, and had to increase steering lock as a result... took a while to get used to but has helped me get quicker & catch the car during the bad times... I need to increase it a bit more still, after hearing you say this I'll give it a try...
I also started another driver file to go back thru the Cup Challenges on semi pro level... so I'm sure the setups will change a bit more... :D
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