Too much gear, too little sidewall, too much pressure?
05-19-2009, 12:47 PM
#1
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Too much gear, too little sidewall, too much pressure?
Late last AutoX season I bought a set of wheels and tires from a fellow S197 owner (Saleen). The tires are 285/30/18 Kumho V710s, about 50% worn.
Their overall diameter is only ~ 25", 2 less than my stock wheels. I also have 4.10 gears, so the overall ratio with the smaller tires is ~ 4.55.
My default tire pressures are 37 front, 34 rear. D-spec settings are 2 turns out front, 3 out rear.
I'm running into a problem where the rear end steps out really easily upon applying the throttle. On my first run I had exited the starting line and had a mini-straight away; I applied the throttle and the back end stepped out immediately. During other parts of the course when I was exiting a mild turn the same thing happened. I'm trying to squeeze the throttle rather than stabbing it but the problem remains.
Do I simply have too much gear (torque)? I admit I haven't messed around with tire pressures enough, but how much of a reduction in the rear would you recommend. Should I also soften the rear shocks more?
Their overall diameter is only ~ 25", 2 less than my stock wheels. I also have 4.10 gears, so the overall ratio with the smaller tires is ~ 4.55.
My default tire pressures are 37 front, 34 rear. D-spec settings are 2 turns out front, 3 out rear.
I'm running into a problem where the rear end steps out really easily upon applying the throttle. On my first run I had exited the starting line and had a mini-straight away; I applied the throttle and the back end stepped out immediately. During other parts of the course when I was exiting a mild turn the same thing happened. I'm trying to squeeze the throttle rather than stabbing it but the problem remains.
Do I simply have too much gear (torque)? I admit I haven't messed around with tire pressures enough, but how much of a reduction in the rear would you recommend. Should I also soften the rear shocks more?
05-19-2009, 02:39 PM
#2
2nd Gear Member
Join Date: Dec 2006
Location: Flanders, NJ
Posts: 408
Vapour,
Of course you know at this point only try making one change at a time. Other wise you will never know what helped and what didn’t. Now having said that I would first equal out your tire pressures, you are on very good rubber with very good dampers. How are the tires wearing front to rear? If you are reaching to the wear marks on the sidewall then don’t change them, past add psi not to the wear mark less psi. That is how I judge the psi on my tires. I think the V710s will need like 35-37 psi cold on our heavier cars. Once you know you are getting good wear out of your tires (you have a good foot print on the ground) then mess with your damper settings. If you are still having the same handling issue, I would either soften the rear or stiffen up the front. I don’t know how the d-specs well at all, Sam would Argonaut too. They might be able to give you some of there settings on race days.
Of course you know at this point only try making one change at a time. Other wise you will never know what helped and what didn’t. Now having said that I would first equal out your tire pressures, you are on very good rubber with very good dampers. How are the tires wearing front to rear? If you are reaching to the wear marks on the sidewall then don’t change them, past add psi not to the wear mark less psi. That is how I judge the psi on my tires. I think the V710s will need like 35-37 psi cold on our heavier cars. Once you know you are getting good wear out of your tires (you have a good foot print on the ground) then mess with your damper settings. If you are still having the same handling issue, I would either soften the rear or stiffen up the front. I don’t know how the d-specs well at all, Sam would Argonaut too. They might be able to give you some of there settings on race days.
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