Let's talk wheel/tire theory
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From: Covington WA, USA
Originally Posted by tinkfist' date='Mar 26 2007, 09:27 PM
It generally holds true because most cars with lots of horsepower usually have lots of torque. The S2000 is a unique car in that it has a lot of power relative to its torque (240/153 = 1.57) where most track monsters today are running at 1:1.
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From: Lewisville, TX
Tom, if you're able to carry more speed through a corner because of the increase in tire width, you'll need less torque to get you going again. Also, you've just installed 4.77's. You now have "hidden" torque.
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From: Farmingdale, NJ
Originally Posted by mikegarrison' date='Mar 26 2007, 11:34 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.
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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?
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From: Encinitas (San Diego), CA
This is too much to read.
Rylan was faster than me last year in Honda Cup, and he had wider tires than me. 'nuf said.
Oh, name a series that have a restriction on how narrow a tire you can run. You'd think thousands of racers and race teams over decades would have figured it out. This may shock you, but serious race teams actually do testing (and have smart engineers too).
Rylan was faster than me last year in Honda Cup, and he had wider tires than me. 'nuf said.
Oh, name a series that have a restriction on how narrow a tire you can run. You'd think thousands of racers and race teams over decades would have figured it out. This may shock you, but serious race teams actually do testing (and have smart engineers too).
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From: Santa Cruz, CA, US
Originally Posted by tinkfist' date='Mar 26 2007, 08:27 PM
Weight difference = 17.8 lbs. Sounds like a lot of unsprung weight to me that is hurting acceleration and braking.
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Originally Posted by rlaifatt' date='Mar 26 2007, 10:38 PM
Oh, name a series that have a restriction on how narrow a tire you can run. You'd think thousands of racers and race teams over decades would have figured it out. This may shock you, but serious race teams actually do testing (and have smart engineers too).
x pi
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Originally Posted by 3312DC' date='Mar 26 2007, 07:14 PM
the only thing inconsistant with that is your 18s were probably super light weight... probably the whole package weighted the same or less than the stock 16s... Now if we could do this comparo with some light 16s, that id like to see.
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Speaking as a guy who doesn't know anything about the specific wheels and tires for S2K applications, here's some data I was able to find quickly on wheel and tire combos out there on the internets:
HRE 547 17 x 10 - 23 pounds
HRE 547 18 x 10 - 25 pounds
Kumho V70A - 335/35R17 - 32.1 pounds
Kumho V70A - 335/30R18 - 29.8 pounds
The 18-inch combo would be .3 pounds lighter than the 17-inch combo. (Overall diameter decreases by a third of an inch.)
Fikse FM-5 17x8.5 16.0 pounds
Fikse FM-5 18x8.5 18.0 pounds
Kumho V710 - 245/45R17 - 23.8 pounds
Kumho V710 - 245/35R18 - 21.6 pounds
The 18-inch combo would be .2 pounds lighter than the 17-inch combo. (Overall diameter is reduced by .9 inches, in this case.)
Granted, I wouldn't put 335's on a 10-inch rim. And granted, I wouldn't trust all the data that's out there on the web. Many increases in wheel diameter also mean an increase in overall tire/wheel diameter, because of the quirks of tire sizing. In those cases, the weight change would skew in the opposite direction.
But it's safe to say that increasing wheel diameter doesn't always mean the rotating mass also increases.
HRE 547 17 x 10 - 23 pounds
HRE 547 18 x 10 - 25 pounds
Kumho V70A - 335/35R17 - 32.1 pounds
Kumho V70A - 335/30R18 - 29.8 pounds
The 18-inch combo would be .3 pounds lighter than the 17-inch combo. (Overall diameter decreases by a third of an inch.)
Fikse FM-5 17x8.5 16.0 pounds
Fikse FM-5 18x8.5 18.0 pounds
Kumho V710 - 245/45R17 - 23.8 pounds
Kumho V710 - 245/35R18 - 21.6 pounds
The 18-inch combo would be .2 pounds lighter than the 17-inch combo. (Overall diameter is reduced by .9 inches, in this case.)
Granted, I wouldn't put 335's on a 10-inch rim. And granted, I wouldn't trust all the data that's out there on the web. Many increases in wheel diameter also mean an increase in overall tire/wheel diameter, because of the quirks of tire sizing. In those cases, the weight change would skew in the opposite direction.
But it's safe to say that increasing wheel diameter doesn't always mean the rotating mass also increases.