Wheels - which size to get for best performance

[Ponyboy]

That's a little over the top don't you think? Let's try to keep it to a discussion. It's tiring to always hear the "You're absolutely wrong" and the "No, you're absolutely wrong" exchanges.

There's been a lot of "discussion" about the advantages of wider tires. From what I understand, all things being equal, a wider tire will provide a bigger tire contact patch. The shape is different also, obviously, because it is wider. The patch shape becomes more rectangular. I think what some get caught up on is the coefficient of friction and how that relates to traction. But, all things being equal, a wider tire will give you a bigger tire contact patch.

 

[SNDSOUL]

I have a great set of 16/17 inch wheels that fit the NSX perfectly and look fantastic on the car. I decided to move up in size, so I hate to see these go, but I need the cash. Check them out in the market place under NSX wheels FS.

Shameless Plug.

 

[nsxtasy]

Wildrice and ponyboy,

Please explain how you can divide 3200 by 32 and come up with an answer other than 100.

 

[wildrice]

The mathematical answer of course is 100. Now, can u tell me what 3500 is divided by 200? And then, what is the cube root of 27?
And then what is the first derivative of the quadratic function?

I just love math, and u must too!!

Lets both join mathprime!!

 

[wildrice]

The Tirerack does have a pretty picture of some contact patchs but they say ABSOLUTELY nothing about the area of the patch. If u are going to attempt to quantify your information at least direct us to a site that supports your position.

 

[1BADNSX]

The wider tire may have a larger contact patch if the car weighs more due to the heavier tires. Or the wider tires could have a larger contact patch if they are inflated to a lower pressure than the narrow tire.

If larger contact patches is all you want, just let most of the air of your tires!

By the way, 17.5, 3, and a linear function.

Bob

 

[nsxtasy]

Originally posted by wildrice:
The Tirerack does have a pretty picture of some contact patchs but they say ABSOLUTELY nothing about the area of the patch.

They say a picture is worth a thousand words. I guess a thousand isn't enough for you to understand.

As long as the tires are reasonably fully inflated, the air in the tires is holding up the car. It does this through air pressure that is applied over the area of the contact patch. The force of the air pressure is equal to the force of gravity. The force of gravity is the weight of the car. The force of the air pressure is applied over the area (number of square inches) of the contact patch at a uniform rate of so many pounds per square inch.

As long as the weight of the car is the same and the air pressure (pounds per square inch) is the same, the size of the contact patch is the same (the weight of the car divided by the air pressure). And that size of the contact patch is exactly the same regardless of whether the tires are 175 mm wide or 335 mm wide, as long as you're not changing the inflation in the tires or the weight of the car.

Do you understand now?

[This message has been edited by nsxtasy (edited 24 April 2002).]

 

[wildrice]

Obviously a thousand words is not enough for you either considering you have near 4000 posts. How many words do you figure that is?

And by the way you are still wrong but I might let you join the mathprime club if you answer the questions right.

And no cheating now.

Refer me to an independent source to substantiate your position - otherwise it is all hogwash.

 

[burbel]

Bob - I believe that the derivative of a quadratic function, in general terms, to be 2ax + b, or a linear function of slope 2a and y-intersection of b.

Boy, I wish tire tech was this simple and straightforward.

I've been spending the night reading a number of sites on this issue, there are the sites that say that wider tires give a different shaped contact patch, and those that say that it "can allow for a significantly wider, shorter tire which can have a dramatic effect on a car's handling, ride and appearance."

I am tempted to believe the first case, that the contact patch area is the same, but that the shape is different. However, what I have yet to see if what differences the contact patch *shape* has to do with performance. Can anyone offer anything on this?

As a possible way to visualize the difference, take two balloons, one round and one cylindrical, place them against a table and push down - the round balloon will make a round contact patch, the cylindrical balloon will make a horizatonal swath-patch. But it's not necessarily more area either way, just different area...

JMO

 

[nsxtasy]

Originally posted by wildrice:
Refer me to an independent source to substantiate your position

http://howstuffworks.lycoszone.com/question506.htm

 

[nsxtasy]

Originally posted by burbel:
I am tempted to believe the first case, that the contact patch area is the same, but that the shape is different. However, what I have yet to see if what differences the contact patch *shape* has to do with performance. Can anyone offer anything on this?

There have been several instances in which magazines have tried different sizes of wheels (using tires with wider tread whenever going to larger wheels) and looked at their effect on lap times. In most cases, differences were slight, but generally showed a slight improvement in going from 15" to 16" wheels, were a wash going to 17", and a decrease in performance going from 17" to 18". The most recent such test was some time last year in Sport Compact Car.

 

[burbel]

I remember reading that article; I guess the thing I am looking for is a description (physics or experience or otherwise) of what truly changes with wider width tires, and why?

If I remember that article, they did it on cars like Civic, etc. The other question is what they did to the suspension when they changed the tire size, if at all...

 

[nsxtasy]

Originally posted by burbel:
The other question is what they did to the suspension when they changed the tire size, if at all...

They didn't make any other changes. And they selected tire sizes which kept the outer diameter of the tire constant, and used the same model tire in all sizes.

[This message has been edited by nsxtasy (edited 25 April 2002).]

 

[wildrice]

I will also attempt to find some independent sources. A picture may be worth a thousand words but if the 1000 words are all DUH!! then how worthwhile is the picture.

Simple minds look for simple "DUH" explanations. Others tend to ferret out the various sources and substantiate their claims with numerous qualified references.


I will attempt to show you how that is done for your future reference.

 

[Lud]

Be nice.

 

[Ponyboy]

Wow. Nice discussion.

I'll try to explain it as best I can w/o my "racing textbooks." I had to go and look at them again since I got my ass handed to me on a sway bar question. Later tonight I'll post references and sources.

For whatever reason, some want more traction. One of the ways of doing this is to increase the size of the tire contact patch. One way to do this is to use a wider tire. All things being equal, a 265/15 tire will have a larger tire contact patch than a 205/15. In general, the contact patch length is the same but it is wider. That increases the tire contact patch size. The wider the patch the more lateral traction. The longer the patch the more straight line traction. As I understand it, road racers want the best balance between a wide and long contact patch. Weight comes in to play when you figure in coefficient of friction and stuff. That's another discussion. But still the rule remains, all things equal, a wider tire will increase the tire contact patch.

 

[nsxtasy]

Shawn,

The weight of the car is the downward force. It is counteracted by the pressure in the tires pushing upward; the two must be equal, because the car isn't moving up or down.

The upward force consists of the pressure in the tires (measured in pounds per square inch) multiplied by the area over which it is applied (the contact patches, measured in square inches).

Because these two forces are equal, the weight of the car equals the pressure in the tires multiplied by the size of the contact patches.

Please explain how the size of the contact patch can consist of two different numbers (one for the narrow tires and one for the wider tires) if the weight of the car is the same and the air pressure in the tires is the same. (Hint: it can't.)

There are some people who incorrectly say that the SIZE of the contact patch is larger with wider tires. The truth is that the size is the same but the SHAPE of the contact patch changes.

[This message has been edited by nsxtasy (edited 25 April 2002).]

 

[wildrice]

I just received a repsonse from Yokohama Tire Company to the following question:

Assuming the same tire inflation and the same vehicle will increasing the tire size from say a 195mm to a 335m increase the area of the contact patch?

They simply stated that the area of the contact patch would be greater with the 335 than with the 195. Not only will the shape of the contact patch be different but the AREA OR SIZE of the contact patch will be greater with the 335 vs the 195.

I would assume that Yokohama Tire Company probably has their facts straight. Straighter than some members of this forum!!!!

 

[nsxtasy]

He or she is wrong.

What's the name of the person you spoke to?

 

[wildrice]

Just go to the Yokohama and post the question.

They provided an answer to my question within 24 hours.

And you have yet to provide empirical, quantative evidence to support your position.

Your two sources provided neither.

 

[wildrice]

Let me put it to you in simple terms that you can understand.

Has anyone actually taken different tires with the same tire pressure on the same identical vehicle and acutally measured the size of the contact patch????

I would be extremely interested in reading the results of that test. You probably cannot find it because the results will not support your hypothesis, yes, at this point that is all it is!!!!

PROVE YOUR POSITION WITH ACTUAL TEST RESULTS.

 

[Lud]

It seems my last message was ignored, so I will try it again more bluntly:

If you cannot make your point without being condescending or abrasive, please don't post here.

 

[nsxtasy]

Measuring the area of the contact patch accurately without the proper equipment is very difficult.

Check out the different shapes of actual contact patches on Toyo's website here and maybe you'll understand why.

[This message has been edited by nsxtasy (edited 25 April 2002).]

 

[wildrice]

By your own definition wider tires will necessiate a wider wheel and thus a wider wheel will weight more and thus increase the area of the contact patch.

Let's assume that you move from a 215 to 285. The wheel width will have to increase thus increasing the weight of the vehicle thus increasing the size of the contact patch or footprint.

The mathematics would be as follows: 3205 divided 32 = 100.16.

Therefore, the reality of the situation is that with a wider tire the contact patch must, by your own definition, increase.

 

[wildrice]

Toyo still does not substantiate your position. Anyway, your own formula must be wrong in reality, since the weight of the car will increase with a larger tire because of the added weight of the wheel.

PS You would also need to factor in the added weight of the tire, so the contact patch would even be larger due to the additional weight.

[This message has been edited by wildrice (edited 26 April 2002).]