Let's talk wheel/tire theory
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From: Farmingdale, NJ
Originally Posted by JackOlsen' date='Mar 27 2007, 01:24 PM
But it's safe to say that increasing wheel diameter doesn't always mean the rotating mass also increases.
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From: Lewisville, TX
Originally Posted by tinkfist' date='Mar 27 2007, 02:50 PM
I agree, but I was referring to the current trend of maxing out the rim you are running on (i.e. 275's on 9" wheels and 245/255's on 8" wheels).
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From: Farmingdale, NJ
Originally Posted by FF2Skip' date='Mar 27 2007, 02:27 PM
Tom, you're putting a 245 on a 7.5" wheel when you use the standby 225/245 on AP1 oem's.
The arguments in here are pretty good (and maybe right), but I've heard lots of stories of people dropping time with a narrower, lighter setup. Not as much as I have heard from those that went wider, but enought to question the cause. Tire/wheel selection is very car specific and the optimum setup is determined by a myriad of factors. I still feel like there is work to be done finding the optimum S2000 setup.
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Originally Posted by mikegarrison' date='Mar 26 2007, 08:34 PM
Be careful here -- the wheel doesn't care at all how much torque the engine has. It only cares about how much torque is at the wheel after the gearing, and that's directly correlated to power.
I can't tell you how many times i've tried to explain that
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From: the tracks around Europe
Originally Posted by cthree,Mar 27 2007, 06:04 AM
Blah blah blah. This is a lot of mumbo jumbo in search of some profound eureka moment which will never come.
Wider tires make perfect sense except in a straight line and in the rain. More traction equals higher cornering speeds with equals higher exit speeds which means getting to the next corner faster which means covering a fixed distance in a shorter time which means lower lap times. Wider tires offer more lateral traction, more traction under braking and more traction under acceleration.
Your 17 lbs amounts to net weight/power ratio decrease of less than 1% (2800lbs/200WHP = 14lbs/WHP vs. 2783/200 = 13.9lbs/WHP) Even if you double the weight savings accounting for it being unsprung and say 13.8lbs/WHP you still aren't closing the margin decreasing the W2P ratio by only 1.4% (effectively gaining ~3WHP). The 235/275 setup nets a contact patch increase of 8.5% vs. 225/245 (1020mm v. 940mm).
Translate that extra 3WHP in terms of what it nets in acceleration down a 1000ft straight and it no where near makes up for the 3-5% increase in corner exit speed, nor the shorter stopping distance (and thus longer straight and higher top speed) you gain from the wider tires. Math bores me but I'm sure someone can do the numbers and prove it. The rolling resistance is roughly equal to 10HP at 65MPH. If you increase that by 8.5% to account for the higher friction coefficient you still only net an additional 1HP.
You spend less time on the brakes, carry more speed through the corner, exit the corner at a higher speed, achieve a higher top speed to the next corner and brake later thus extending the length of each straight between corners. Do it over and over and you start counting seconds per lap.
So would you rather have a car which exits a corner 5% faster or one which has 2-3% more horsepower?
Wider tires make perfect sense except in a straight line and in the rain. More traction equals higher cornering speeds with equals higher exit speeds which means getting to the next corner faster which means covering a fixed distance in a shorter time which means lower lap times. Wider tires offer more lateral traction, more traction under braking and more traction under acceleration.
Your 17 lbs amounts to net weight/power ratio decrease of less than 1% (2800lbs/200WHP = 14lbs/WHP vs. 2783/200 = 13.9lbs/WHP) Even if you double the weight savings accounting for it being unsprung and say 13.8lbs/WHP you still aren't closing the margin decreasing the W2P ratio by only 1.4% (effectively gaining ~3WHP). The 235/275 setup nets a contact patch increase of 8.5% vs. 225/245 (1020mm v. 940mm).
Translate that extra 3WHP in terms of what it nets in acceleration down a 1000ft straight and it no where near makes up for the 3-5% increase in corner exit speed, nor the shorter stopping distance (and thus longer straight and higher top speed) you gain from the wider tires. Math bores me but I'm sure someone can do the numbers and prove it. The rolling resistance is roughly equal to 10HP at 65MPH. If you increase that by 8.5% to account for the higher friction coefficient you still only net an additional 1HP.
You spend less time on the brakes, carry more speed through the corner, exit the corner at a higher speed, achieve a higher top speed to the next corner and brake later thus extending the length of each straight between corners. Do it over and over and you start counting seconds per lap.
So would you rather have a car which exits a corner 5% faster or one which has 2-3% more horsepower?