The difference is in the slip angle. The tire with the wider contact patch (but equal in size) develops a smaller slip angle, which is a performance advantage.
Wheels - which size to get for best performance
- Thread starter DONYMO
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You are correct. IF the larger wheel/tire combination weighs more (which depends on the wheel/tire used), then the contact patch will be larger - not because of the wider tires, but because of the increase in weight. In the example you gave, it would increase by 0.16 percent (about one sixth of one percent).
This discussion deserves it's own thread doesn't it?
Just to be clear, we're comparing the same diameter of the tires, both inflated to their correct vertical load distribution, with the width being the variable, right?
Seems like the real question is if it's possible to actually increase the size of the tire contact patch and not just it's shape.
Just to be clear, we're comparing the same diameter of the tires, both inflated to their correct vertical load distribution, with the width being the variable, right?
Seems like the real question is if it's possible to actually increase the size of the tire contact patch and not just it's shape.
Andreas, thanks for the reply. Do you know of a nice source that can explain slip angles in terms I can understand? I tried the "How to make your car perform" or some such book, the one that covers suspension tuning for 1990's cars, with a race Camaro on the cover, but I guess I just couldn't follow it.
Yes, I am right and by using your own formula. And for some reason you have embraced a theory that has no substantive, quantative or empirical evidence.
Don't you think it is strange with all the members that no one has come forward with evidence to support your position. There is an old saying - believe nothing that you hear and only half of what you read. I got a lead on some diamond mines in Illinois, are u interested in investing?
In reality it is imopssible not to increase the contact patch because of the increasing weight of the wheel and the tire. Not that I believe your theory, which I don't, I am just using it to negate your proposition that the contact patch's area will not change - it will!!
And yes, I did contact Yokohama tire company on their e-mail site and they simply said that a wider tire will not only change the SHAPE of the contact patch but will also increase the SIZE of the contact patch.
I would suggest that you explore your position with the various tire companies and post your results on this forum!!
I am beginning to feel like a dog chasing its tail and will not post another reply to this topic until you support your position with something other than innuendo and oblique references.
Don't you think it is strange with all the members that no one has come forward with evidence to support your position. There is an old saying - believe nothing that you hear and only half of what you read. I got a lead on some diamond mines in Illinois, are u interested in investing?
In reality it is imopssible not to increase the contact patch because of the increasing weight of the wheel and the tire. Not that I believe your theory, which I don't, I am just using it to negate your proposition that the contact patch's area will not change - it will!!
And yes, I did contact Yokohama tire company on their e-mail site and they simply said that a wider tire will not only change the SHAPE of the contact patch but will also increase the SIZE of the contact patch.
I would suggest that you explore your position with the various tire companies and post your results on this forum!!
I am beginning to feel like a dog chasing its tail and will not post another reply to this topic until you support your position with something other than innuendo and oblique references.
The "How Stuff Works" website link that I posted is a well-regarded reference.
You have still not shown how you can divide the weight of the car by the air pressure in the tires and come up with two different numbers for the area of the contact patch, depending on the width of the tires.
[This message has been edited by nsxtasy (edited 26 April 2002).]
Re-read my post. I referred you to the Toyo website only to show different shapes of tire contact patches in order to illustrate the difficulty in measuring their size.
Your post dated 4/23/02 @1:21 states that whether your running 205/50-15 or 275/30-18
the size of the footprint will not change but the shape will change.
Can you tell me where I can find a set of 18's with 275's that are equal in weight to 205's with 15's? The REALITY of the situation is that you CAN'T!
The only point that I am trying to make, now for the third and LAST time, is that based upon your formula, WHICH I DON'T SUPPORT, the footprint will change in SHAPE and INCREASE IN SIZE. This is because of the additonal weight of the wheel and tire.
Therefore, your statement is incorrect with respect to the example that you used. In fact, it is incorrect with respect to most tire and wheel increases because of the ADDITONAL WEIGHT!
Again, I challenge you to support your hypothesis with empirical evidence.
PROVE ME WRONG!!!!
the size of the footprint will not change but the shape will change.
Can you tell me where I can find a set of 18's with 275's that are equal in weight to 205's with 15's? The REALITY of the situation is that you CAN'T!
The only point that I am trying to make, now for the third and LAST time, is that based upon your formula, WHICH I DON'T SUPPORT, the footprint will change in SHAPE and INCREASE IN SIZE. This is because of the additonal weight of the wheel and tire.
Therefore, your statement is incorrect with respect to the example that you used. In fact, it is incorrect with respect to most tire and wheel increases because of the ADDITONAL WEIGHT!
Again, I challenge you to support your hypothesis with empirical evidence.
PROVE ME WRONG!!!!
Dear Mr. "I don't care if Lud wants me to be nice":
That is NOT what my post says. Here is what it says:
"The size of the contact patch depends only on the amount of air pressure in the tires and the weight of the car (assuming that the tires are fully inflated so that the air in the tires is supporting the weight of the car). If the car weighs 3200 pounds and you have 32 psi of pressure in the tires, the size of the four contact patches will be 100 square inches - regardless of whether the tires are 205/50-15 or 275/30-18."
In other words, as long as the car weighs the same, the contact patches will have the same size. THAT is what it says. It's quite possible that the larger tires weigh a different amount; it could be more OR less. It's also quite possible that the larger wheels weigh a different amount; that, too, could be more OR less. It's even possible that you are comparing two wheel/tire combinations in which the weight remains the same, because you've found 18" wheels that are lighter by exactly the same amount that the 15" tires are heavier.
The fact is, I don't think that anyone here except wildrice is worried about changes of a fraction of a percent due to changes in the weight of the wheel/tire combination. Furthermore, I don't think that anyone has the explicit objective of adding weight in order to increase the size of the contact patch on the tires, which your logic would seem to imply.
There is a common misconception that wider tires have a significantly larger contact patch, BEYOND any change caused by the greater weight of the wheel/tire combination. This misconception is simply not true.
I spoke today with one of the country's top tire experts, John Rastetter at the Tire Rack, whom I have had the pleasure of meeting at our local BMW Club meeting. (I believe he has an article about tires in the current issue of Grassroots Motorsports.) He confirmed that they have found that this is true - that the size of the contact patch does NOT change significantly when comparing tires of different widths, using the same air pressure in the tires. (wildrice, note the word "significantly", meaning that small changes due to the weight of the tire are considered insignificant.) He said that the Tire Rack, working along with the tire manufacturers, have tried measuring the actual size of the contact patch on various width tires on the same car, and they found that in all cases, the measurement showed them to be within a third to a half a square inch of each other (with these relatively insignificant differences likely due to measurement error as much as anything else). That is empirical evidence from the experts.
Done.
[This message has been edited by nsxtasy (edited 26 April 2002).]
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You know it doesnt really matter who is right because who runs the tires with full pressure at the track anyway. My 275/40/17 grip much better than the 255/40/17 I had before, at the same pressure, on the same wheel, on the same car, driven by the same person(me). Who needs math, put the tires on the car judge for yourself.
I've thought about all the posts wrt to footprint and or contact patch and decided that in reality I don't give a hoot about about the subject and that NSXTASY has given it alot more thought than I have and is probably right and therfore yield to the superior warrior.
To the victor go the spoils. Enjoy!!!!
To the victor go the spoils. Enjoy!!!!
Well, actually, the problem is not that you are arguing with Ken (a favorite passtime on Prime and an activitly I highly encourage), but that you are arguing with physics. The fundamental gas laws support Ken's position. Sorry, the universe wins; you loose.
The transition in your arguement to the calim that you meant the contact patch increases due to the added wieght of larger tires is a rather transparent attempt to save face and really has nothing to do with the point of the discussion. By your reasoning, we could increase the contact patch by adding a few hundred pounds of ballast to our cars. Okay, so what? That was inherent in Ken's initial post, is blatantly obvious, and does not add anything to the discussion.
I love to see debate on this forum, as I consider it to be the best way to fully examine any issue; however, its usefulness as a leraning tool is limited by the willingness of all participants to keep an open mind, truely listen to the other participants and accept when someone else presents a clearly superior arguement.
BTW, anyone who has been interested enough to read through the entire thread should check out this article on the issue.
Have a nice day.
[This message has been edited by David (edited 27 April 2002).]
Good link. Probably the best one I've seen on the web. And yet, this morning I've rumaged thru 3 books that imply that "wider is better" - from an increasing contact patch POV. Note Pontiac Grand Prix reference.
So, there's two schools of thought on this?
From what I've read, it is possible to actually increase a tire's contact patch. And from what I can tell, the variable is psi. So, supposing a thinner tire adjusted to correct vertical load and a wider tire adjusted to correct vertical load (same diameter), the wider tire will have more contact patch. No?
Yesterday, talking to formula mazda guy and one of his mechanics, they said they got 20 inches of contact patch at the front and 22 inches of contact patch at the rear. The rear had a wider tire. He said they've been running this way for years. I didn't get to talk to them much after that, they had to prepare and stuff, so I didn't get to ask him about width and diameter and how he measured it and stuff.
From what I've read, it is possible to actually increase a tire's contact patch. And from what I can tell, the variable is psi. So, supposing a thinner tire adjusted to correct vertical load and a wider tire adjusted to correct vertical load (same diameter), the wider tire will have more contact patch. No?
Yesterday, talking to formula mazda guy and one of his mechanics, they said they got 20 inches of contact patch at the front and 22 inches of contact patch at the rear. The rear had a wider tire. He said they've been running this way for years. I didn't get to talk to them much after that, they had to prepare and stuff, so I didn't get to ask him about width and diameter and how he measured it and stuff.
Actually, the Pontiac Grand Prix ads, IIRC, show that a wider distance between the wheels are better, not wider wheels themselves.
As for the Formula Mazda, I think it might have more to do with weight distribution. Imaging (be easy on me) 2400 lbs and all tires at 24psi, that would give 100 square inches of contact patch. However, over the rear wheels we have the majority of the weight, say 60% rear, 40% front. That would make the contact patches 20 square inches in the front and 30 each in the rear. With the weight distribution from the NSX - wasn't it 40/60 - and 32psi, these would be the contact patch areas as well, correct? See, I told you I wanted to keep it easy.
Again, lowering the PSI in any type of tire should (within reasonable limits) increase the contact patch of the tire, with similar tire types. If the tire pressures are the same, then the contact patch should be the same (or, from some of the actual data I've seen, be withing a few square millimeters. For an idea of what a square millimeter really is, consult this period.
As for the Formula Mazda, I think it might have more to do with weight distribution. Imaging (be easy on me) 2400 lbs and all tires at 24psi, that would give 100 square inches of contact patch. However, over the rear wheels we have the majority of the weight, say 60% rear, 40% front. That would make the contact patches 20 square inches in the front and 30 each in the rear. With the weight distribution from the NSX - wasn't it 40/60 - and 32psi, these would be the contact patch areas as well, correct? See, I told you I wanted to keep it easy.
Again, lowering the PSI in any type of tire should (within reasonable limits) increase the contact patch of the tire, with similar tire types. If the tire pressures are the same, then the contact patch should be the same (or, from some of the actual data I've seen, be withing a few square millimeters. For an idea of what a square millimeter really is, consult this period.
burbel, I learned about slip angles from Paul Frere's Sports Car and Competition Driving, but this book is overly analytical. The definition of slip angle is simply the difference between the direction a wheel is pointing in and where it's actually going. Read the following short article to understand how slip angles come about.
http://www.microsoft.com/games/precisionracing/cart/racingschool1.htm
As much as it pains me to link to a Microsoft site, I think this easy-to-read introduction is just what you're looking for.
That is indeed an excellent article. Thanks for posting the link, David.
Originally posted by Ponyboy:
And yet, this morning I've rumaged thru 3 books that imply that "wider is better" - from an increasing contact patch POV. Note Pontiac Grand Prix reference.So, there's two schools of thought on this?
Wider MAY be better; wider tires can certainly be expected to change handling and other performance characteristics, often (if not always) for the better. I think it is just a common misconception that this happens because of the size of the contact patch changes, when in fact it is the shape that changes rather than the size. Those who observe changes in handling simply make the wrong (but understandable) conclusion about the mechanism causing those changes.
If you change the pressure in the tires, you can indeed change the size of the contact patch. However, there are lots of reasons for changing tire pressures, and it is not normally solely done to adjust for tire width and/or to increase the size of the contact patch, except at the drag strip (where it is done to increase the size of the contact patch).
As burbel correctly notes, there may be different sized contact patches front vs rear, and this depends on the air pressure (which may also be different front vs rear) and the weight distribution front vs rear, not the width of the tire (except for the insignificant differences in weight of the wheel/tire combo).
HTH
[This message has been edited by nsxtasy (edited 28 April 2002).]
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