Wider tire means better grip?

[Andrie Hartanto]

Is it true? Well, the March and April Race Car Engineering discussed this very issue on the consultant column.

Let me put it this way. You bet they are!!! It also actually say that the contact patch is bigger. The most common conception on A=Fn/P is not necessarily true. It is all depends on the tire manufacturer, stiffer sidewalls, etc.

Race Car Engineering is one magazine that actually cover lots of technology aspect of automotive. Lots of the column are very technical and some of them requires engineering background to understand.

 

[NSX-Racer]

Did they write something different as we did here in some threads? e.g.: that wider tires (given that they are the same brand and type, compound, tire pressure) don't do much better for acceleration (they may even decrease it) and braking but can give you a bit more corner speed? Had something to do that the contact patch has not a different size but a different shape AFAIK.

 

[Ponyboy]

Say it ain't so Andrie! I'll pick up this issue during lunch at work. Thanks for the heads up.

FWIW, I've got a great tech book on tires that says the same thing though probably in a different way.

 

[MvM]

Well, this is one issue I really would like to know a bit more off.
I remember different threads here where it was explained that bigger tires still have the same size of contact-patch on the road but just in a different shape. All because of the weight of the car in combination with the tire-pressure used.
At the same time however, in many articles I've read, writers have stated they thought that the OEM-tires for the NSX were too small to achieve maximum cornering-speeds. Same kind of articles also sometimes state that cars like the Corvette and Viper achieve their high cornering limits because of their very big tires.
Also, when I look at F1-cars I see a car that is very, very light and still is using very big tires. So, ground-pressure cannot be much but cornering speed is still extremly high.

 

[NSX-Racer]

That's no contradiction, Maarten. Exactly the same was written in the threads you mention (abbreviation in my former post here).
Only one statement is not true: The NSX OEM tires are not too small to achieve maximum corner speeds - it's a question of compound. And of course you achieve maximum corner speed with (non street legal) soft race slicks, even more than you would have with - let's say - 335 mm street legal tires...

 

[RP-Motorsports]

I can't wait to hear Ken's response to this!

 

[NSX-Racer]

I can't wait to hear Ken's response to this!

You already find a lot of Ken's responses in this ole thread. :wink:

 

[AU_NSX]

I can hear Scotty now....

"But Jim, you cannot change the laws of physics..." :wink:

Andrie great post!... How about posting the article for us who can't buy the magazine...

 

[Ponyboy]

Here's the book in question:

http://www.amazon.com/exec/obidos/A...6/sr=2-1/ref=pd_bbs_b_2_1/103-8274642-3877413

I went ahead and did my own contact patch comparo and the 285 did indeed have more area than the stock 225. Not by the amount I expected but still a bigger area.

 

[Ponyboy]

Here's the informal comparo originally posted on H-T.

I did a little test of my own comparing the contact patch of a 285/30-18 to a 225/50-16 and it came out pretty interesting. The 285 patch was close to an inch and a half wider and a 1/4 shorter. Measurement is a little tricky when both sizes are static and maybe a little more easy in a dynamic state. Unless I did something wrong in figuring this out, the 285 S0-3 has 18% more contact patch than the 225 A022. I was expecting to see both tires to have the same total area but with different shapes. Wider= wider but shorter. Narrower= narrower but longer. This is true but the total areas are different.
What I came up with:
- 225/50-16 has 30.9 square inches of contact patch, 7 inches wide by 5.25 inches long.
- 285/30-18 has 36.3 square inches of contact patch, 9.3 inches wide by 5
Criteria used:
- Tires: Yokohama A022 (24.9 inches in diamater) and Bridgestone S0-3 (24.7) at 35psi.
- Car measured on the rear driver's side wheel, 2 degrees neg camber.
- Wetted bottom of tire down with Formula2000 and put white construction paper underneath tire.
- Measured as an ellipse: length times width, divide by four, multiply by pi. Can also measure as a square though dynamically the footprint more resembles an ellipse.

The theory formula for measuring contact patch is weight of corner divided by lbs. per square inch, which would confirm that both tires have the same area though different shapes. Though in this experiment the the wider tire has more footprint. But I'm not sure if you could make a general inference out of this or if you could just say that a 285 S0-3 has more footprint than a 225 A022. Unless there's a factor I haven't considered yet.

<= was also going to compare a 205 vs. a 235 but couldn't fit the 205 over the Stoptechs.

Anyone want to send me a 225/50-16 S0-3?

 

[NSX-Racer]

Before Ken does the writing I may add that you compared of course different brands and types which may even lead to different patch sizes with the same tire sizes. Did someone post the measures for the smaller Bridgestone?

 

[Ponyboy]

Exactly, good point. Which is why I qualified the "experiment" with:

"But I'm not sure if you could make a general inference out of this or if you could just say that a 285 S0-3 has more footprint than a 225 A022. Unless there's a factor I haven't considered yet."

I just did the best I could with what I had on hand. Nobody posted the measurements of the smaller Bridgestones but Ken did put me in a headlock and gave me a wedgie in subsequent posts. :wink:

 

[CokerRat]

Very interesting... I always wondered about the calculation for contact patch because it seemed to conflict with the observation that big fat rear tires were used for ultra-high performance cars. It makes sense for an easily deformable object (like a balloon) but tires, especially ones with short and stiff sidewalls, do not totally conform. In fact now that I think about it, it falls apart at low pressures -- ie. contact patch approaches infinity as pressure approaches zero. Obviously more force is required to flatten the rubber at the edge of the contact patch than at the center. So that suggests the weight is not evenly distributed across the contact patch (front-to-rear), and then it would make sense that a short but wide patch would best distribute the load. Am I reading this right?

 

[NSX-Racer]

CokerRat: I guess you need different tire inflations for different purposes - e.g. Drag racers (and Dakar sand rallye drivers) have extremely low pressures to increase traction by widening the contact patch.

Track racers like we try to get an even wear across the tire (that's what we achieve with measuring the hot temperatures across the patch and decrease pressure when the middle is hotter than the edges and vice versa) because we need not only traction in one direction but also lateral.

 

[Andrie Hartanto]

How about posting the article for us who can't buy the magazine...

Unfortunately, I don't have a scanner.
Secondly, it is about 4 pages long. Don't feel like typing that much here
Hopefuly someone else that has the magazine can scan the article. BTW, it is a series article started on March issue.

 

[Ponyboy]

Picked up the April issue at lunch. It gets fairly technical. But here's the Cliff Notes version:

Okay, summing up, what does a wider tyre get us?

- It runs cooler, and/or
- it makes more effiecient use of its contact patch by having a greater % adhering, and/or
- it can run at lower inflation pressure and therefore actually have a larger contact patch, and/or
- it can have greater lateral stiffness at a given pressure and therefore keep its tread planed better, and/or
-it can use a softer, sticker, faster-wearing compound without penalty in longevity.

 

[1BADNSX]

Unless there's a factor I haven't considered yet.

Shawn, yes you forgot to mention the tire pressures were precisely measured and were the same. Of course the easiest way to increase contact patch size is to decrease the tire pressure to near zero, but of course that isn’t the fastest way around the track.

Tire width isn’t much different than most other issues, there is an optimum. If you take an extremely heavy wide tire on a low power car, it will have slower lap times for other reasons than grip. Skinny tires will be slow period. Find the first derivative!

Bob

 

[Ponyboy]

Hi Bob,

I suppose you're talking about my "informal test?" Yes, it was certainly not scientific but I did the best I could with what I had and controlled as many variables as possible. BTW, I didn't forget it. Both tires were at 35 psi as accurately as I could measure them. I used the same digital gauge which was accurate to a tenth.

Tires: Yokohama A022 (24.9 inches in diamater) and Bridgestone S0-3 (24.7) at 35psi.

 

[nsxtasy]

bigger tires still have the same size of contact-patch on the road but just in a different shape. All because of the weight of the car in combination with the tire-pressure used.

True. If you have a 3000 pound car, and its weight is being supported by the inflation of the tires with air pressure of 30 psi, the size of the four contact patches is going to total 100 square inches. It doesn't matter whether they are 335 mm wide gumballs or 185 mm wide skinnies; as long as the weight of the car is supported by the tire inflation, the relationship still holds - 3000 divided by 30 is always going to equal 100. Note that when tires are NOT normally inflated, such as with run-flat tires that have been punctured, then the sidewalls support a portion of the weight, so this relationship is no longer true.

The Technical Director at the Tire Rack notes that they have measured the size of contact patches of two tires of substantially different widths, on the same vehicle with the same inflation, and they found that the size of the two contact patches was identical, within the accuracy of their measurements (less than 2 percent error). So this book differs with what the Tire Rack found. Knowing how very high the level of expertise at the Tire Rack is when it comes to tires, I wouldn't place a whole lot of reliance in anything that this book says. They obviously didn't consult with the experts in their field.

At the same time however, in many articles I've read, writers have stated they thought that the OEM-tires for the NSX were too small to achieve maximum cornering-speeds.

The theory behind those who claim that wider tires allow faster cornering is that it is achieved due to the difference in the SHAPE of the contact patch, and not due to any difference in the SIZE of the contact patch. (Most such folks know enough about the physics to realize that there isn't any difference in the size of the contact patch.) In all of the actual, real-world tests I've seen, that is true only up to a certain point; for example, when speaking in terms of wheel sizes, when you go plus one or plus two, you may improve lap times, but they worsen when you go wider beyond that point.

 

[1BADNSX]

Both tires were at 35 psi as accurately as I could measure them.

Shawn, sorry I missed the "35 psi" in the original post.

Bob

 

[ncdogdoc]

......So this book differs with what the Tire Rack found. Knowing how very high the level of expertise at the Tire Rack is when it comes to tires, I wouldn't place a whole lot of reliance in anything that this book says. They obviously didn't consult with the experts in their field.

Well, Paul Haney, the author of this book, is an expert in this field, and has consulted on many race teams and worked for a major tire manufacturer (Goodyear?). Two excellent articles in SCCA Magazine last year on tires and how they changed the handling of the car by him.

 

[nsxtasy]

Well, Paul Haney, the author of this book, is an expert in this field, and has consulted on many race teams and worked for a major tire manufacturer (Goodyear?). Two excellent articles in SCCA Magazine last year on tires and how they changed the handling of the car by him.

Maybe he and the folks at the Tire Rack should get together and do their contact patch measurements at the same place and time...

 

[Chris F]

It always unnerved me that a wider tire had more adhesion than a narrower tire, considering only the same compound in a non-overheating temperature.

The lateral acceleration ought to be the static coefficient of friction of the rubber material itself, times g. No more no less. Tire pressure, contact patches and trick suspension be damned.

Of course, this isn't the case. I like simple physics, but cars aren't quite so simple.

I add this, to note that you can't always predict test results basaed on known good simple physics, in a complex system such as a car.

-Chris

 

[Andrie Hartanto]

Maybe he and the folks at the Tire Rack should get together and do their contact patch measurements at the same place and time...

Yeah, it would be nice to know the credential of those people behind tire rack, and their method of measuring them.

 

[nsxtasy]

Yeah, it would be nice to know the credential of those people behind tire rack, and their method of measuring them.

Credentials? They're the top experts in the whole tire industry! (A lot of them are racers as well.)