500whp.com

iTrader: (86)

yes you are right more toe out will give you faster turning into corners!


\ / <--------- imagin thats your front tires! if you make a right, or left you will see the tires will react faster

Hiboost

iTrader: (9)

I also see some problems with the rule of thumb on tire pressures stated by the poster and I've read it that way before wondering what the author was thinking... to get more oversteer and reduce understeer you INCREASE tire pressure above optimum grip so that the rear of the car has increasingly less grip than the front. Raising tire pressure is similar to increasing effective spring rate, slightly narrows the contact patch, and reduces grip on that end of the car if you are going above the optimum setting. Now if you went too low up front at the same time they might actually cancel each other out but if you kept the front at Optimal and raised the rear above optimal you will get more overstear and a loose rear end. Since I usually strive to get higher effective spring rates on the street cars I drive, I can't think of a reason on street tires where I would keep the front at optimum and lower the rear pressure below optimum to lower traction. Perhaps with stiff sidewall race tires this is reasonable but for a vast majority of people here it wouldn't make sense.

ultraflip

iTrader: (1)

sweet! thanks jeff! this will totally help me with my settings on GT4!!!

500whp.com

iTrader: (86)

The list are thing that you can do to adjust for either under or oversteering! Yes if you adjust to get more understeering you will get less over steering!

The list i got it from they have been in the racing suspension business for years and years, they tune many pro racing cars!

Hiboost

iTrader: (9)

Yes but we have street cars, atleast the vast majority of us still do. Lowering the air pressure below optimum to lower traction seems counterproductive on street tires as you will get rollover onto your sidewalls under severe cornering and the car will feel sluggish and unresponsive. Flog your car around on street tires while autocrossing and lowering pressures is just not an option without risking a tire pealing off the wheel!

The first thing the novice instructor will tell you to do is to get the air pressures increased at all four corners in the same ratio that the factory recommends. If the car won't turn (Understeer) and the fronts are at optimum pressure, raising the rear pressures over optimum to loose some traction will give you some oversteer. Really what you want to do is find a suspension that has perfect balance without having to adjust any tire pressures away from their optimum grip. Reason being is that using tire pressure to reduce traction at one end of the car gives you less overall traction in exchange for better control for the driver. In general lower pressure is more traction up until you begin to get rollover onto the sidewalls but can also build up more heat in the tire and increase rolling resistance. A good driver can go a little slower to get the most out of a suspension for a faster time, where as an aggressive driver will end up going slower by overdriving the car.


While tuning the car's suspension to perform properly is important, just about any expert will say to tune the nut behind the wheel before making any major changes. Personally I like a car that has minimal body roll, agile steering, and neutral handling. I like it when full power is drifting evenly and letting off gets you a little oversteer depending on steering angle so that when you put your foot back in it where you steer is where you go. For stiff sidewall race tires things may be different, anyone else want to explain it better?

white05evoVIII

iTrader: (1)

great post. i agree this should be a sticky

FarNorthRacing

I thought I knew a lot about tires until I got a couple of drunk Avon engineers talking....

It can be really hard to characterize how a tire will react to a change in tire pressure, because so much depends on the construction of the tire, and because it depends on where you start.

For a radial, R-compound tire, all else being equal, raising pressure will increase total lateral grip, but will also make the line between "I've got it" and "It's got me" narrower. It may also reduce acceleration/braking grip slightly.

Over a certain point though, adding more pressure will reduce grip, not increase it.

Rules of thumb are a good starting point, but especially for those of us who build and race production-based cars, you have to learn which of those rules of thumb apply, which work opposite, and why (and how much)

Hey, if it were easy, *everybody* would do it, right?

DG

Kayaalp

iTrader: (1)

Sure. But again, that assumes the suspension is already optimized. Our cars have too little negative camber up front, are too high, and the springs are too soft. If we try to "optimize" the grip of our tires, it quickly becomes clear that the rear has WAY more grip than the front. So you have to sacrifice some rear grip (by bumping up the rear pressures past the "ideal") to have a balanced cornering attitude.

With my stock suspension, an aggressive alignment with max neg. camber up front (about -1.8 deg.), and stock Advans, I find my car has an almost perfectly neutral handling balance when I keep my front pressures at 40 psi (hot) and the rears at 41.5 psi (hot). Sure, you sacrifice some "ulimtae" grip, but the car is MUCH faster around a course when you can drive it consistently at the limit.

Emre

Deetz

iTrader: (1)

All of this is recreating the wheel (pun not intended!)

Caroll Smith's - "Engineer in Your Pocket" A pratical guide to tuning the race car chassis and suspension. ISBN 0-9651600-1-7

This is a "flip-chart" like guide that goes into way more detail about all aspects (entry - mid/set - exit) of balance and correction. Get it (although sometimes hard to find) and be amazed.

On topic - The best and most profound advice a suspension engineer once gave me - "Look to the opposite end of the car" if you have a problem. Most times everyone corrects the symptom and not the cause...

"There was once a cripple whose left arm was lame. He came across a Genie in a bottle, and wished that his one arm be like the other. The man now begs in the streets with two lame arms..."

Deetz.