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Old 09-14-2007, 07:30 PM   #1
BuggeyEYED
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Default 18" wheels for track with 500+hp?

I'm guessing this is the perfect section to post in to get an answer from the actual people (and if not, please move to an appropriate place).......I've been searching the site all day and it seems like alot of high horsepowered wrx/sti's (500+hp) run 18's but some run 17's? Does the weight/size hurt you at the track. Would larger wheels slow you down or actually add MPH up top?
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Old 09-14-2007, 07:48 PM   #2
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The heavier the wheel is, the more inertia it has and the more energy it takes to change it’s movement. It also takes energy to rotate something...which makes you move off the line and down the track slower, maybe a tenth slower but every little bit helps, so why hurt yourself
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Old 09-14-2007, 07:50 PM   #3
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Quote:
Originally Posted by blowbyu24 View Post
...so why hurt yourself

What about the guys running brake kits requiring 18" rims...?
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Old 09-14-2007, 07:53 PM   #4
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give and take man
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Old 09-14-2007, 07:55 PM   #5
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^^^Thats when you've calculated that the heat dissipation qualities of the larger brakes will make enough of a difference over the course of a race to counter the bit you might loose to the added mass of the larger wheel.
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Old 09-14-2007, 08:01 PM   #6
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so an 18" wheel weighing the same as a 17" wheel (maybe has a big lip for ex.)will not make a difference?
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Old 09-14-2007, 08:27 PM   #7
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Most drag cars use smaller diameter wheels for less weight (rotational mass), larger width for more traction, and sticky.

It all really depends on your setup.

If there was one correct answer there would only be one size Drag Wheel.


8.341 @ 158.69mph (small wheel, big tire)
http://www.tonyrigoliperformance.com..._drag_car.html

http://www.tonyrigoliperformance.com...n_dragcar.html

http://www.tonyrigoliperformance.com...g_sti_rwd.html

big dog, small wheel, big F**ckn tires
http://www4.army.mil/OCPA/uploads/la...-06-125745.jpg
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Old 09-15-2007, 01:43 AM   #8
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Even if an 18 inch wheel weighs the same as a 17 inch wheel it still takes more energy to move the 18 inch wheel. An 18 inch wheel is an inch farther away from the center than a 17 inch thus the 18 inch wheel requires more energy to move
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Old 09-15-2007, 01:06 PM   #9
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^^^

Depends on the wheel and tire.

My 18" Volk TE37's weigh LESS then the tires. So reducing the tire size, is reducing where the real weight is....
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Old 09-15-2007, 03:55 PM   #10
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but thats the weight though, you still have the 18" diameter to go around rather then the 17 correct?
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Old 09-16-2007, 12:29 AM   #11
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You guys are forgetting about Aspect Ratio

A 225/50/17 has a larger overall diameter than a 245/40/18 for example...

I like this site: http://www.miata.net/garage/tirecalc.html
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Old 09-16-2007, 09:04 AM   #12
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Quote:
Originally Posted by BuggeyEYED View Post
but thats the weight though, you still have the 18" diameter to go around rather then the 17 correct?
Overall diameter is the same as stock. I have a 18" wheel with lower profile tires....

Not sure what you are getting at....
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Old 09-16-2007, 09:09 AM   #13
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On a street car? It doesn't matter. It's not going to make a substantial difference unless you are running some 40-lb 22s.
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Old 09-16-2007, 08:48 PM   #14
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Take it from someone that has about 150 passes on his Subaru. The smaller the wheel and tire the faster your car will be. I did some testing and it makes a much larger difference then most people think. Even if the rim is lighter, The tire mass is farther out on the edge of the overall wheel and tire. If in doubt try it. I found 3 tenths going from light ass 18's to heavy ass stock 16's.

clark
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Old 09-17-2007, 04:15 PM   #15
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Quote:
Originally Posted by AZScoobie View Post
Take it from someone that has about 150 passes on his Subaru. The smaller the wheel and tire the faster your car will be. I did some testing and it makes a much larger difference then most people think. Even if the rim is lighter, The tire mass is farther out on the edge of the overall wheel and tire. If in doubt try it. I found 3 tenths going from light ass 18's to heavy ass stock 16's.

clark
true. You would have to make the tire/wheel combo for an 18" wheel quite a bit lighter to get the same results as running a 17" wheel/tire that are the same over all weight. (Because of rotating mass)

Side note wider tires make huge difference too. there are lots of factors in racing wheels/tires. It all depends on what you are racing.
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Old 09-17-2007, 04:27 PM   #16
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I understand what I'm reading but I'm also interested if the only racing done is on a road coarse.
It's more easily understood looking at the 1/4mi. but once up to speed is there a slight advantage to 18's that may negate the hit you take off the line that makes it a non issue on a road course?

Sorry if I hijacked, just curious.
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Old 09-17-2007, 06:05 PM   #17
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Quote:
Originally Posted by medamullet View Post
true. You would have to make the tire/wheel combo for an 18" wheel quite a bit lighter to get the same results as running a 17" wheel/tire that are the same over all weight. (Because of rotating mass)

Side note wider tires make huge difference too. there are lots of factors in racing wheels/tires. It all depends on what you are racing.
so wider is not better either? 8.5 too big?
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Old 09-19-2007, 03:34 PM   #18
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It all depends on what you are racing. I track my car and I can't push it hard enough for the stock 225's to give me problems. I run my stock 17 x 8 rims with stock tires. (they are good tires, everyone wants to get rid of there on here to get 18, 255's) So I can pick up stock tires cheap and run them hard and hot.

Like I said it all depends how much TQ your car is putting down and what kind of racing you are doing. I am in no way a pro, but I do track my car and stock is good enough for me, cheap and easy to get. Spend your money on something different, Best money spent to make your car faster is driving lessons.
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Old 09-20-2007, 02:20 AM   #19
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Quote:
Originally Posted by stealth06wrx View Post
Even if an 18 inch wheel weighs the same as a 17 inch wheel it still takes more energy to move the 18 inch wheel. An 18 inch wheel is an inch farther away from the center than a 17 inch thus the 18 inch wheel requires more energy to move
Actually half an inch farther away. I know exactly what you meant though.

Proof positive that a wheel at the same weight and two different diameters has two different rotational masses. The larger one is harder to stop because it has more rotational force. Also, the outer edge of the rim on a 18" rim covers more ground than the outer edge of a 17" rim. this can be seen when the mexicanos put those shorty little rims/tires on their whips they are killing their gas mileage and their top speed. Its okay though, they are saving weight.
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Old 09-20-2007, 12:16 PM   #20
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Quote:
Originally Posted by BuggeyEYED View Post
so an 18" wheel weighing the same as a 17" wheel (maybe has a big lip for ex.)will not make a difference?
So you guys already forgot your high school and college physics? It's all about rotational moment of inertia. As some have already stated above, even if an 18" wheel/tire combo has the same overall weight as a 17" wheel/tire combo, it will take more energy to spin an 18" combo because it has more mass further away from the center of rotation.
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Old 09-20-2007, 12:25 PM   #21
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