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Influence of wider tires on the track ?

Old 09-30-03, 03:45 PM
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Influence of wider tires on the track ?

Can anyone share any experiences/thoughts on how th wider tires would affect the car handling/lap times on the track ? Also, how does the wheel size (e.g. 16" vs. 17") affect those ?

I'm running 225/50/16 atm but would like to know whether I should go with something like 245/40/17 or just 245/40/16 or something similar ?

Do wider tires actually offer more grip compared to stock tires ?

Thanks!
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Old 10-01-03, 03:40 AM
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No-one knows ?
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Old 10-01-03, 03:49 AM
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im not really sure about this as i have no first hand experience and just gather this from people that do.

wider tires=wider contact patch on the road

meaning(theoretically) more grip. more grip, turn faster, overall faster on the track.

the only bad thing about that i have heard from switching to larger diameter wheels is the change in your overall final drive. if you switch to larger wheel but change to smaller sidewall enough that you dont change the overall diameter of the tire, you should be ok. there are alot of 16-17 wheels that rival the weight of 14-15s.

hope that helps...
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Old 10-01-03, 08:56 AM
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There are too many variables that are unknown to answer your question.

1). You can find tires in the same size as stock that are better tires that will lower lap times. Different designs, compounds, etc. all affect a tires grip, and how long it will last. Hoosiers of the same size as stock will GREATLY improve lap times, but will not last long at all.

2). what wheels are you using? Different size wheels will affect tires differently. If the wheels you are using now are the perfect size for stock size tires, then only going to a bigger tire may round off the larger tire by trying to sqeeze it on the rim, and go slower. Again, this must be matched to the wheel, which a lot of tire dealers can help you with.

3) The wheel/tire size will also increase contact patch, ever so slightly. a 225 16" tire will have slightly less contact than a 225 17" tire will due to the larger diameter. you can offset the gearing idea of larger wheels with a lower aspect ratio to get a larger wheel size with the same tire overall diameter.

I know this doesn't answer your question directly, but there is not enough info to start with. And way too many opinions on tires and their performance to say this tire and this wheel with this setup will drop your lap times this much.

Cheers
Travis
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Old 10-01-03, 10:20 AM
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Re: Influence of wider tires on the track ?

Originally posted by cruiser
Can anyone share any experiences/thoughts on how th wider tires would affect the car handling/lap times on the track ? Also, how does the wheel size (e.g. 16" vs. 17") affect those ?
Boy, this is a can of worms just waiting to be kicked over. Uh, where to start ... wider tires offer larger contact patches which will increase grip. What does that net you? Higher entry speed, later braking, and earlier throttle application. However, wider tires will not be as crisp on turn-in and response is marginally slower than the narrower counterpart. Also, wider tires are generally heavier, so you are adding unsprung weight. But, that's a tradeoff that 99.999% of racers will take all day, any day.

Wheel width affects the amount of tire width you can run. But, that should not be directly correlated to wheel size. You can run a 265/40 16 on a 16x10 wheel ... getting that to fit on your RX-7 is another story altogether. Most tires do actually have a larger contact patch as you increase wheel diameter and retain section width ... i.e. a 245/40 17 will be significantly wider than a 245/45 16. Again, bigger wheels mean more unsprung weight. More grip versus less weight? That's your call. Suspension tuning is a game of give and take ... you have to make the decisions on what best suits you.

If you want a more punitive education on tire and wheel sizing, here's a book I can suggest for you:

"How to Make Your Car Handle" by Fred Puhn.
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Old 10-01-03, 12:10 PM
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I have had first hand experience with track times and tire size. My race car had 15x8" wheels with used BFG Road Race tires. At TGPRI I was turing around 1:14's. This was with a high mileage stock motor with low compression on one chamber.

A few months later I had a new ported motor and 15x10's with full Slicks (Yokahoma). Again the best I could do was 1:14's at TGPRI. I discovered that I could hold much more speed through the turns but the car felt like it bogged down out of the turns and would not acclerate as fast past ~55 mph. I discussed my apparent performance issues with some more experience races. They suggested that I had gone TOO BIG with the tires. I had more rolling resistence than before, more air resistence as well as more weight. The performance gain of grip in the turns was not enough to overcome the loss of accleration due to the size.

In a more powerful car (ie: turbo) there might not be as much of a gap loss than I experienced.
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Old 10-01-03, 09:21 PM
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I went from 225/50-16 on 8 x 16 to 255/40-17 on 9 x 17. Laptimes drop 1 to 2 seconds at both Mid Ohio and Putnam Park. Tire differences were slight. 225/50-16s were Pirelli P-Zero Asimmetricos. 255/40-17 were Yokohama AVS Intermediates. Wheel/tire weight increased. Old stock size was 38 lbs--wheel/tire inflated to 32 psi. Larger size was 45 lbs. If you can afford to upgrade wheel width, diameter, and tire size, and your rules allow, I'd say go for it. It does make a difference. Note the wheels were the same style. 8 x 16 and 9 x 17 wheels were both SSR Integral A2s. The 8 x 16 (38-mm offset) was 16 lbs each, and 9 x 17 (45-mm offset) was 19 lbs each. Track widths were about the same for each size wheel/tire (based on the offsets), so only the increased tire contact patches and slight difference in tire brands were the major changes.

Last edited by SleepR1; 10-01-03 at 09:25 PM.
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Old 10-02-03, 06:23 AM
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Thanks SleepR1, that was the answer I was looking for
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Old 10-02-03, 06:28 AM
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I didn't change sizes, just compounds. I came across a good deal on stock rims and tires and decided to get them as extras to throw race tires on. Rims were stock but tire size went from 225/50 16 to 245/45 16, on same rims. Got a heck of a deal ($100) on a used set of Hoosiers.

At Sebring, (3.7 miles, 17 turns) went from 3:02 to 2:48. Huge difference. I'll never run on street tires again. Amazing how much more fun it is to do most of the passing versus getting passed.

My .02, worry more about the tire compound than the size.

David
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Old 10-03-03, 08:52 AM
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I don't want slicks atm, as tracking days are only like 5 a year. Not worth it. And I'm in top5 already
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Old 10-03-03, 09:39 AM
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Try Volk SE37K with Toyo RA-1 tires. Not the stickiest r-compound tires, but will last long enough for you to enjoy the five track days you do. Sizes will be 9 x 17, 40-mm offset with 255/40-17 tires.
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Old 10-03-03, 09:49 AM
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Originally posted by CarmonColvin
I discovered that I could hold much more speed through the turns but the car felt like it bogged down out of the turns and would not acclerate as fast past ~55 mph. I discussed my apparent performance issues with some more experience races. They suggested that I had gone TOO BIG with the tires.
Yeah, sometimes you can make the car TOO tight and not be able to free the car up at corner exit.
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