MUST READ!: Wheel Width Considerations - Lexus IS Forum
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post #1 of 33 (permalink) Old 04-19-2011, 11:52 AM Thread Starter
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MUST READ!: Wheel Width Considerations

For those running crazy offsets and such, this is a good read. Also good for those of you picking out wheels and wanting to make sure you don't harm performance in the process:

Wheel Tech, Part II: Width Matters | Tuner University

The PDF at the end of the article from an engineering firm on the topic is pretty darn good tech reading too.

Hope this helps someone.

OEM is best.
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post #2 of 33 (permalink) Old 04-19-2011, 04:36 PM
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Lol nice read. Should be stickied. There are too much misinformation regarding wheels, tires, let alone hellaflush.

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post #3 of 33 (permalink) Old 04-19-2011, 05:04 PM
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This article is going to be Earth shattering for alot of people here lol great read though. Kinda has me reconsidering the width I wanna go with when I get some new wheels.

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post #4 of 33 (permalink) Old 04-19-2011, 07:16 PM
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I'm pretty sure most people running 8.5" tires on 10" wheels don't care about performance. Also, he's making the change in scrub radius most people will see with wider wheels and tires that don't require huge flares a much bigger deal than it really is. But still, there are a couple good parts.
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post #5 of 33 (permalink) Old 04-19-2011, 08:38 PM
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Quote:
Originally Posted by Brian_ View Post
I'm pretty sure most people running 8.5" tires on 10" wheels don't care about performance.
This, I have my car for looks and my car for the track. Race cars dont win shows and show cars dont win races. Only mod on my IS300 is a catback exhaust and a short ram intake. No LSD and stretching a 225 on an 18x10 and I still don't spin the tires, haha.
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post #6 of 33 (permalink) Old 05-05-2011, 11:04 PM
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Part III.

Wheel Tech, Part III: Wheel Diameter’s Effect on Performance | Tuner University

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post #7 of 33 (permalink) Old 05-06-2011, 07:50 AM
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Yeah this should be stickied. Basically what I got from all 3 parts is the closer you stay to all of the stock dimensions of the wheel and tire, the better the all around performance is going to be in all categories and the stock wheels and tires are there because they were tested as being the most efficient. Upgrading one factor of your wheel/tire combo is gonna cause a shortfall in another category. Its all about trade offs.
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post #8 of 33 (permalink) Old 05-07-2011, 11:31 PM
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that was a long article but very interesting.. So many people say that wider or lower profile is better, just shows you that you can't always believe what you hear just because so many people say it.
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post #9 of 33 (permalink) Old 05-12-2011, 10:15 AM Thread Starter
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There are also these which would be good for most folks here....

(Part IV)

Wheel Tech, Part IV: Tires – The Most Important Performance Part | Tuner University

and probably a little more "common knowledge" but still interesting and brings some more information to light:

Wheel Tech, Part I: Wheel Weight Slows You Down | Tuner University

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post #10 of 33 (permalink) Old 05-12-2011, 01:41 PM
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After reading the four wheel posts I have been rethinking my upcoming wheel tire decisions. I was planning on a slight increase in wheel width (7 to 8 inch) and accompanying that with an increased tire width (215/45 to 245/40). Originally thinking that the increase in width would increase my overall grip characteristics. Applying the information from the links I wont have any performance advantage with the increased width, but only improved tire life (more material in contact and less heat generated).

Thinking about contact patch not affecting grip seems like a strange concept. Why do racers adjust tire pressure if contact patch has no effect? a lower pressure will increase tire pressure while a higher pressure will decrease contact patch. With friction(grip) not being affecting by contact patch, you should be able to run any pressure and have identical characteristics.

I have to be missing something to tie it all together. But, I cant think of anything from past schooling to add anything to it.
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post #11 of 33 (permalink) Old 05-12-2011, 01:59 PM
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BY popular demand, this thread is stickied for now.

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post #12 of 33 (permalink) Old 05-12-2011, 03:01 PM
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Very good read. Will go back and read all the other parts before purchasing new wheels. I was thinking of going with 9.5" wheels, but I may reconsider after reading this.

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post #13 of 33 (permalink) Old 05-12-2011, 03:43 PM
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Quote:
Originally Posted by KMis300 View Post
Thinking about contact patch not affecting grip seems like a strange concept. Why do racers adjust tire pressure if contact patch has no effect? a lower pressure will increase tire pressure while a higher pressure will decrease contact patch. With friction(grip) not being affecting by contact patch, you should be able to run any pressure and have identical characteristics.

I have to be missing something to tie it all together. But, I cant think of anything from past schooling to add anything to it.
I think you may have misread something. I recall the article said contact patch area is a direct function of pressure (inverse relation). The lower the pressure, the bigger the contact patch. What (I recall) the article said was going to a fatter tire does not give you more traction. Going to a fatter tire (while keeping the tire pressure the same) gives you the same amount of contact area and friction, but with a wider tire the contact patch will change it's shape to a skinnier shape which will aid with cornering, but will yield LESS traction for acceleration and deceleration. Strictly speaking friction = mew/fn. Mew is the coefficient of friction between the two material in contact, and fn is the normal force.

PS. Running your tires at low pressure is not a good idea either. You will lose fuel economy, and the sidewall will be subjected to a LOT more compression and rebound every rotation leading to more stress and possibly premature wear on the side walls and possibly your sidwalls blowing out.

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post #14 of 33 (permalink) Old 05-12-2011, 04:48 PM
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^^Very good point Johnny. A lot of people don't know all the facts and this thread really helped me understand as well. Thanks for the article too SmallboostingIS! Must spread love tho.

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post #15 of 33 (permalink) Old 05-13-2011, 09:11 AM
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Quote:
Originally Posted by Johnnysks View Post
I think you may have misread something. I recall the article said contact patch area is a direct function of pressure (inverse relation). The lower the pressure, the bigger the contact patch. What (I recall) the article said was going to a fatter tire does not give you more traction. Going to a fatter tire (while keeping the tire pressure the same) gives you the same amount of contact area and friction, but with a wider tire the contact patch will change it's shape to a skinnier shape which will aid with cornering, but will yield LESS traction for acceleration and deceleration. Strictly speaking friction = mew/fn. Mew is the coefficient of friction between the two material in contact, and fn is the normal force.

PS. Running your tires at low pressure is not a good idea either. You will lose fuel economy, and the sidewall will be subjected to a LOT more compression and rebound every rotation leading to more stress and possibly premature wear on the side walls and possibly your sidwalls blowing out.
I understand there are limits to how much tire pressure you want to run. Also, their affects on fuel economy. However, I'm looking at tire size and compound from purely a performance point of view. My point was using the assumption a tires grip is based off of F=muN (lateral force=friction*normal force) it wouldn't matter what size your contact patch was. It simply doesn't come into the equation. This model works if we're using a smooth surface (no grip). The problem with this model is we cant use F=muN to model how a tire will grip (only works for modeling static friction, but characteristics change when we get close to our limit). This is the point when we begin to realize the difference of grip tires are able to use. We're tearing the rubber off (very thin layers) rather than sliding over the top the way friction is modeled. Using friction to model tire grip is what I was attempting to justify and due to change in properties it cant be used.
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