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Old 09-28-2012, 11:08 PM   #21
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Ive got a question for you. What is the contact area for a 16" vs a 15" of the same width and aspect ratio? Do you think its actually the same?
Your question is too general in nature. The contact patch is based on more than just wheel diameter and tire size. Tire construction, air pressure, car weight, camber,etc. are just a few of the variables that determine the size of the contact patch and shape. Even with that info I'm not the one who could do the appropriate calculations. The length of the contact patch varies very little between tires close in overall diameter. The width of the tire is what is responsible for the bulk of the contact area.
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Old 09-29-2012, 01:42 AM   #22
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I find it interesting that people are under the impression that the width of the tire, all other factors the same, creats the larger contact patch by virtue of width but what about patch length? Which tire, with the only variable being the wheel diameter, creats the larger contact patch? the 15 or the 16? this is on an identical car, by the way. thanks for answering. I hope more fanatics chip in.

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Old 09-29-2012, 02:34 PM   #23
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From a purely scientific standpoint, aka physics, and with all things being the same (especially both tires supporting the same weight and having the same internal air pressure) but excepting the overall diameter, the size of the contact patches will be identical. The contact patches will, however, vary in shape.

But things are not always the same in the real world. As a tire gets taller (or shorter for that matter) the construction of the tire changes (even between the same make and model) as well which ends up distributing the weight its bearing differently. Furthermore, as the volume of the tire changes the need for differing internal pressures may also be required to maintain load carrying capacity and tire shape.
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Old 09-29-2012, 08:49 PM   #24
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Quote:
Originally Posted by Geezer View Post
From a purely scientific standpoint, aka physics, and with all things being the same (especially both tires supporting the same weight and having the same internal air pressure) but excepting the overall diameter, the size of the contact patches will be identical. The contact patches will, however, vary in shape.
this is my belief.

wide tires have wide but short contact patch. narrow tires have narrow but long contact patch. total area is the same

contact patch area in sq.inch is as simple as total vehicle weight divide by 4 tires divide by PSI in the tire.

you can get the approximate contact patch length, by divinding the area by the tire width.

ex. 2800lb car / 4 / 35psi = 20 sq inch per tire

with my 275 wide hoosier race tires (11in), the contact patch is 1.8" long.
with my 195 wide snow tires (7.8"), the contact patch is much longer 2.6"
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Old 09-29-2012, 09:39 PM   #25
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Actually, there are several formulas that dispell the idea of similar contact patch area of wide vs not wide. One of these can be found in The Automotive Chassis: Engineering principles, 2nd edition. You can find one of the formulas on BND TechSource website.

Your contact area is greater on your 195's than your 275's.
11x1.8=19.80"
7.8x2.6=20.28"
Kinda confusing, huh? Of course, I'm very easily confused. Comes with old age!
What pressure are you running cold in your Hoosiers?

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Old 10-01-2012, 08:30 AM   #26
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Quote:
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I hope more fanatics chip in.

Bill
Well, I think we have all the tire nerds available on FF in this thread now

And we may have ran off the OP with contact patch discussion...

My track day experience is not extensive, but everytime I've gone wider in tire I've been faster. So the answer becomes, if you really want to go faster, you have to test, test, test. Find out what combo makes the car feel the best and go the fastest.
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Old 10-01-2012, 09:57 AM   #27
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Well, I think we have all the tire nerds available on FF in this thread now

And we may have ran off the OP with contact patch discussion...

My track day experience is not extensive, but everytime I've gone wider in tire I've been faster. So the answer becomes, if you really want to go faster, you have to test, test, test. Find out what combo makes the car feel the best and go the fastest.

The wider tire theoretically should provide more lateral grip resulting from the wider contact patch. A lot, however, depends again on tire construction, more importantly on tread compounds to maximize the adhesion of that wider contact patch. I think we all understand that a sticky narrower tire will outperform a wider tire that has a tread as hard as a hockey puck.
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Old 10-01-2012, 10:41 AM   #28
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I would look at a Toyo Proxes RA1 225/50/15, my recommendation would be to have then shaved, full tread they are a bit squirmy. And being your probably running stock camber they won’t wear all that even, so your better saving them and rotating them frequently.
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Old 10-01-2012, 10:57 AM   #29
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I don’t see any rims listed on tire rack that fit your car in 15” but I think you should be able to fit a 15” over the brakes you. From what I found is the front rotor on that car is 278mm I run 15” OZ on my SVT and the stock brake are 300mm I have to shave down the caliper ever so slightly. With a little searching you should be able to fine a 15” x 7” rim
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