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post #16 of 33 (permalink) Old 05-13-2011, 03:22 PM Thread Starter
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contact patch matters, read part IV on tires to get a better idea of why. It's not so much for grip, as it is for more practical reasons (Temperature for starters)

OEM is best.
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Last edited by smallboostingIS; 05-13-2011 at 03:29 PM.
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post #17 of 33 (permalink) Old 05-13-2011, 04:17 PM
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Sounds like this guy's never been on a track. Lets all get motorcycle tires... as long as the scrub radius isn't changed, the driving dynamics won't change. The principles he learned in his physics class don't necessarily make him a crew chief ready to set up a race car.

From someone with experience with an is on a track, tire compound is definitely the best way to improve grip. Tire pressure and alignment are key. Wider tires ARE better though. Given the same tire pressure, the contact patch may be the same surface area, but a wider contact patch lets you get around corners faster and that's how you improve your times.

Go to your local autocross and look at competitive cars in classes that restrict suspension geometry changes. They're all at the limit of the class rules in both tire compound and tire width, I guarantee it.

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post #18 of 33 (permalink) Old 05-13-2011, 06:38 PM
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I like how people are criticizing others for believing what they read on forums by citing some random dudes blog.
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Originally Posted by BERK View Post
Sounds like this guy's never been on a track. Lets all get motorcycle tires... as long as the scrub radius isn't changed, the driving dynamics won't change. The principles he learned in his physics class don't necessarily make him a crew chief ready to set up a race car.
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post #19 of 33 (permalink) Old 05-14-2011, 09:15 AM Thread Starter
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what's funny is...if you read the full series, you'll find that everything you just said is exactly what is in the article . Specifically, tire compound is the only way (for the average enthusiast) to increase grip. That's extensively covered in part IV.

Also, understand that there are extremes both ways (Also covered in various parts of the articles)...too narrow is just as bad as too wide, actually, worse.

As for other parts, I think you'll find several SAE papers and experienced racers that agree

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Last edited by smallboostingIS; 05-14-2011 at 09:21 AM.
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post #20 of 33 (permalink) Old 05-15-2011, 01:59 AM
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Quote:
Originally Posted by Johnnysks View Post
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.
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Originally Posted by BERK View Post
From someone with experience with an is on a track, tire compound is definitely the best way to improve grip. Tire pressure and alignment are key. Wider tires ARE better though. Given the same tire pressure, the contact patch may be the same surface area, but a wider contact patch lets you get around corners faster and that's how you improve your times.
Much of what you said was in the article and I've already quoted. When you said "better", you meant for lateral acceleration. However, you should keep in mind most people thinks they need wider tires as they're putting down more power, when in reality by going to a wider tire they're trading off linear traction for lateral traction and in effect are making it more worse. However, going to a heavier tire and rim probably rob them some of the power and helped them to not break traction in a very counter productive way.

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Originally Posted by smallboostingIS View Post
what's funny is...if you read the full series, you'll find that everything you just said is exactly what is in the article . Specifically, tire compound is the only way (for the average enthusiast) to increase grip. That's extensively covered in part IV.
You guys should read the article before you criticise it as most of the criticism was actually covered in the article as well as previous post in this same thread.

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post #21 of 33 (permalink) Old 05-15-2011, 02:13 AM
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Quote:
Originally Posted by KMis300 View Post
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.
I was refering to mu, the coefficient, as in better rubber = better traction. I wasn't saying fn is a good model.

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post #22 of 33 (permalink) Old 05-15-2011, 02:22 AM
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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.
The point of the article was keeping the same tire pressure (and thus contact area size) does not give you more linear traction, and going to a wider tire while keeping the same tire pressure will give you more lateral traction. Racer lower pressure to increase contact surface area. The article mentioned that as well.

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post #23 of 33 (permalink) Old 05-15-2011, 03:35 AM
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Quote:
Originally Posted by Johnnysks View Post
friction = mew/fn. Mew is the coefficient of friction between the two material in contact, and fn is the normal force.
MEW




Quote:
Originally Posted by Johnnysks View Post
Much of what you said was in the article and I've already quoted. When you said "better", you meant for lateral acceleration. However, you should keep in mind most people thinks they need wider tires as they're putting down more power, when in reality by going to a wider tire they're trading off linear traction for lateral traction and in effect are making it more worse. However, going to a heavier tire and rim probably rob them some of the power and helped them to not break traction in a very counter productive way.
If you honestly think that my car is slower in a straight line or around corners because I run 265s, your ideas are 'more worse' than I thought.

Quote:
Originally Posted by Johnnysks View Post
You guys should read the article before you criticise it as most of the criticism was actually covered in the article as well as previous post in this same thread.
Quote:
Originally Posted by smallboostingIS View Post
what's funny is...if you read the full series, you'll find that everything you just said is exactly what is in the article . Specifically, tire compound is the only way (for the average enthusiast) to increase grip. That's extensively covered in part IV.

Also, understand that there are extremes both ways (Also covered in various parts of the articles)...too narrow is just as bad as too wide, actually, worse.

As for other parts, I think you'll find several SAE papers and experienced racers that agree
I hadn't read pt4 of the article until now, and agree that there are some good points that help bring pt3 into focus. In fact, I'd say that this thread should begin with the caveat that pt3 should be taken with a grain of salt until pt4 is read.

I still think that the article relies too much on the classroom and not heavily enough on the track though. Heat dissipation is a huge part of why wider tires result in more grip, but you fail to consider the centripetal force acting on the mass of the tires as they rotate, resulting in a reduction in the length of the contact patch.

Also, you fellows are claiming that wider tires increase the 'lateral' grip, while sacrificing 'linear' grip. How many people with 1IS's are honestly afraid of giving up a little straight line grip to get around a corner faster? Last time I dynoed, I put down nearly 500 whp, and I still wouldn't hesitate to make that trade. Any n/a 1IS should have no trouble at all putting down the power unless the camber is f***ed, which may or may not be the case with many of the cars on this site.

My last point is, once again, don't take my word, go to a track. Time attack cars, competitive autocross cars, other cars running on stock suspension geometry DO NOT run stock tire width. Of course, there is a limit to everything, there is a point at which the width gets excessive, but unless you've hacked your fenders off completely, I wouldn't worry about it.

EDIT: Please excuse me if I've offended anyone; I did drink tonight, and I'm not very good at keeping to the pl.

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Last edited by BERK; 05-15-2011 at 03:51 AM.
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post #24 of 33 (permalink) Old 05-15-2011, 11:02 AM
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Quote:
Originally Posted by BERK View Post
MEW

Hmmm, I'd have to say that is a pretty weak come back. I don't have a key for on my keyboard, and yeah, my greek hooked on phonics tape never arrived ...

Quote:
Originally Posted by BERK View Post
If you honestly think that my car is slower in a straight line or around corners because I run 265s, your ideas are 'more worse' than I thought.
No one is saying that. If you read carefully and think about it, all we are saying is you'll have less traction in a straigh line by running 265's. Less traction will not affect your acceleration unless you're breaking traction. Remeber, traction is a variable force, and only represents the maximum force available. And as we've stated, traction also depends on the coefficient of friction between the two material, thus the rubber compound matters.

Quote:
Originally Posted by BERK View Post
Also, you fellows are claiming that wider tires increase the 'lateral' grip, while sacrificing 'linear' grip. How many people with 1IS's are honestly afraid of giving up a little straight line grip to get around a corner faster? Last time I dynoed, I put down nearly 500 whp, and I still wouldn't hesitate to make that trade. Any n/a 1IS should have no trouble at all putting down the power unless the camber is f***ed, which may or may not be the case with many of the cars on this site.
That is the point. The article is meant to be informative. It was meant to debunk that wider tires give you more traction period. The point was IT IS A URBAN LEGEND. You don't gain more traction. You have the same traction, but your contact patch is changed. It is up to the *educated* end user to decide if they want more linear traction or lateral traction, which would depend on their application. As I've already said, we often see post about users wanting more linear traction for drag racing and ask about fitment for wider rim and tires, which would be counter productive to their objective.

Quote:
Originally Posted by BERK View Post
My last point is, once again, don't take my word, go to a track. Time attack cars, competitive autocross cars, other cars running on stock suspension geometry DO NOT run stock tire width.
None of us are disagreeing with that. Time attack and auto cross both involve turning, and it would be advantageous to have a good balance of lateral and linear acceleration. For those applications, it does make sense to go to a wider tire. The article covered that as well.

Dood, not sure why you're getting your feathers all ruffled when the article said pretty much the same things as you did.

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post #25 of 33 (permalink) Old 05-15-2011, 05:04 PM
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Contact patch of a tire is not *only* dependent on tire pressure. A tire with zero gauge pressure stands alone(unlike a balloon). A rolling tire's diameter can change. Why does a car with -3* of camber in the rear have less traction if it's contact patch is the same size? You need to consider the way a tire deforms under dynamic loads.

I've read my share of texbooks, and could probably dig up books to argue on both sides of the argument. I remember learning in my high school physics class exactly what you are telling me. mu=Ff/Fn. Surface area doesn't even play a role in that equation, but that is a very simplified version assuming two smooth objects. HERE's some interesting reading regarding the actual friction force a tire experiences. Excerpt 2 discusses the changes in shape of the contact patch under various loads and at different slip angles. Under slip is when a tire actually generates it's maximum grip, at which point the high school level physics is left way behind. Look up the LuGre Model if you're curious and somewhat sadistic.

I honestly don't care about the textbooks though, I'd much rather rely on experience. And my experience tells me that my car is better at putting down the power with 265s than it was with the exact same tires in a 245, period.

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post #26 of 33 (permalink) Old 05-15-2011, 06:57 PM
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I read the articles but still somewhat confused, So they are saying our 215's on our 7 inch wide tires are as good or better then 9 inch rears with 275's because of the contact patch and the way the suspension is set up? I am going to be running 500rwhp and was going to buy some wider rims, so i want to get this straight before wasting my money.
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post #27 of 33 (permalink) Old 05-16-2011, 10:16 PM
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As everyone in this thread can agree, the fastest way to improve grip is tire compound, but stickier tires means they don't last as long. I would certainly tell you that wider is better, but obviously not everyone here agrees. I will advise you that if you do get 275s in the back and you ever want to go around a corner at speed, don't neglect the front tires. You're definitely not going to fit 275s, but go as wide as you can.

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post #28 of 33 (permalink) Old 05-13-2012, 07:00 AM
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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 #29 of 33 (permalink) Old 04-05-2013, 08:50 PM
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So what is the widest you can go without affecting performance? Im assuming you can go at least 7.5 wide because thats how wide the L'tuned wheels are.
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post #30 of 33 (permalink) Old 04-05-2013, 10:38 PM
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It's not affecting performance per say. It is about trading accelerating/braking traction for turning traction.

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