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Old 09-27-2007, 11:25 AM   #19
eTiMaGo
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AFAIK more pressure = smaller, less conformant contact patch = less grip. Hence, more pressure at the back will encourage the rear tires slipping.
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Old 09-27-2007, 11:52 AM   #20
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Etimago's explanation is spot on.
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Old 09-28-2007, 12:06 AM   #21
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At the old autox track I used to run the car with a 40lb front and 42 to 44 lb rear. The newer track which is alot smoother I run 40 front and 42 back with coilovers set stiffer than usual in the rear. Tires are Azenis 615's 215, 45,16's.


For the road tracks I don't want as much oversteer. I run on even tire pressure and adjust the coilovers to stiffer in the front and about 30% softer in the rear.
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Last edited by mojoyaris; 09-28-2007 at 12:27 AM.
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Old 09-28-2007, 12:35 AM   #22
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Quote:
Originally Posted by Boy Blue View Post
I did not remove the spare or any of the trays from the rear of the car...
I was running stock shocks.
The track temperature was warm, but not hot.
Not sure if I completely understand the under/oversteering thing..
Going into the corner I would push the car through, sliding on the tire till the apex of the corner, comming out I would be spinning and pushing through as well. (maybe my cornering speed was too quick?)

Is a front strut bar really going to make enough of a difference?
When I first took my car out to Autox I ran it on lowered springs, 17 in rims and ziex 512's (215 size). The tires surely chunked..........
To get the rear end around, I increased the rear pressure to 45 and the fronts to 42. To prevent the car from pushing I used the brakes and steering to unbalance the car on the next lap to get the back end up and around, but this also produces a bit more oversteer than you may want. ... but it's fun! If you want a neutral turn in and out, the best way is brake before the turn, not during the turn.

When you're getting wheel spin exiting out of the corner it's because, well you're gassing it too hard. An LSD to keep the power to the ground does help.

Hopefully this and the others will help you on your next time out.
Have fun!
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Old 10-23-2008, 06:18 PM   #23
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High rear pressures are good, so stay on that track. Same thing with rear springs, I have used as high as 950 lbs/in in front drive cars that didn't want to turn.

Your big issue is front camber, as the photos show a lot of positive camber. This is where your chunking issues are coming from, and also your understeer, as it is making your contact patch smaller and making you corner on the sidewall. Ideally, there would be a much larger rear bar available that matches with a significantly larger front bar in order to get a good balance and control the roll issues of this car.

Adding weight to the front of the car will worsen your understeer issues. You want to move it to the back if possible, this is why a 911 wants to oversteer while a Mustang wants to understeer during steady-state cornering (it's also the reason that World Challenge touring cars have the driver sitting in the back seat). However, the amounts of weight we are talking about are not going to significantly effect the handling.

Also, slow in/fast out may help keep the tires on the car, but you are then going to be slow, not just because it means earlier braking zones and lower entry speeds, but because you are asking the car to do a LOT of work on the power, which is when it wants to push. Use brakes and entry speed to get the tail out at entry. Oversteer is your friend here. Don't worry about making it "too oversteery", because this car pushes so much that it would take A LOT of work, money, and time to get this car anywhere close to that. No one is going to accidentally find it with a set of shocks.

In a properly set up fwd racer you actually want to throw the car in while trail braking in order to get the back to rotate so that it is pointed when you go back to power. Also keep in mind that a good fwd car MUST oversteer off the throttle, because if it is neutral on the way in, it will be such an understeering pile of crap on the way out that it will not be worth driving (fwd cars come from the factory like this). Properly driving a car like this is a game of toss and catch. You throw it in, let it get sideways, then catch the slide with your throttle application.

If you have never driven a good front wheel drive race car, the first time you do you will think it is broken, as they just want to get sideways all the time. This is the only way they can be balanced when power is applied.

Good luck!

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Old 10-23-2008, 06:34 PM   #24
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I just noticed that this thread is ancient. Damn hackers got me all confused and out of turn.
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Old 10-23-2008, 09:34 PM   #25
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Quote:
Originally Posted by eTiMaGo View Post
AFAIK more pressure = smaller, less conformant contact patch = less grip. Hence, more pressure at the back will encourage the rear tires slipping.
What I've found is that there is an optimal pressure range.

Sometimes more pressure (up to a point) gives better traction because of less contact patch and sidewall deformation.
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Old 10-23-2008, 10:10 PM   #26
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I agree with all the tyre pressure tricks and camber......

I reckon the best mod is to get some camber bolts and put more negative camber. To me, this had quite a big effect on reducing understeer.
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