Tyre width vs contact patch

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Saf4
This is really bugging me!

http://www.performancesimulations.com/fact-or-fiction-tires-1.htm

According to the article the contact patch of a wide tyre is the same of a narrow one per given load due to increased lateral longitudinal deformation for decreased width. But then why do performance cars have eg 345s? and 205s on "practical" cars to decrease road noise?
 
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Saf1
This is really bugging me!

http://www.performancesimulations.com/fact-or-fiction-tires-1.htm

According to the article the contact patch of a wide tyre is the same of a narrow one per given load due to increased lateral deformation for decreased width. But then why do performance cars have eg 345s? and 205s on "practical" cars to decrease road noise?
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Thats not what I got from readin the article:

"It is apparent that increasing the contact patch width indeed increases contact patch area."

"Wide tires have a greater contact area? From this data it appears very likely."

Sounds like a wider tire has a bigger contact patch to me... When changing tire width, the width of hte contact patch should stay the same, its the length of the contact patch the changes increasing the area of the contact patch.

The other thing to take in to account is the rim width used and tire pressure. Too skinny of a rim on a wide tire reduces contact patch and may not give much more than stock.... ie 8" rim with a 315 v a 10" rim with a 315, the wider wheel shoudl have a bigger contact patch...

I personally experienced a big increase in traction going from a 245 > 315 on the back on my car, same brand and model tire.. Also the correct tire pressure does play in to this. On the road course on street tires we have to be careful and find the right pressure so that you have an optimum contact patch...
 
As has been said that's not what the article or the data says at all.

This is one of those situations in which the rough (and they are rough) formulas used by those who subscribe to the "determined only by load and pressure" don't cover what happens in reality nor cover the complexities of the how tyres work (and one I have been partially guilty of in the past).

Yes it is true that load and tyre pressure are part of the factor in determining the size of the contact patch, however they don't scale directly (twice the load doesn't give you twice the contact patch size) and a number of other factors also get forgotten. Such as on a narrow tyre as load increases/pressure decreases you will get a longer contact patch, but you will also get sidewall deformation (which will increase as pressure drops and/or load increases) which will reduce the rate of contact patch growth and also the limits by which it can grow in length based on when the radius of the rim itself starts to play a role.

All of this is also just looking at static contact patch size and shape, the second you apply lateral and/or longitudinal forces then how narrow tyres vs wide tyres react changes once again, regardless of if they did or did not have the same size contact patch.
 
To put it quickly, a wider contact patch may not be bigger in area, but it's still wider. Also those really wide tires probably have really low treadwear (they're grippy).
 
SpartanG
To put it quickly, a wider contact patch may not be bigger in area, but it's still wider. Also those really wide tires probably have really low treadwear (they're grippy).
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Unless you are going with a tire that has significantly different load capacitied or make up, the width of the contact patch should not change much based upon the same load. There wil be some minor variations, sure, but the width of the contact patch itself will be very similar based upon the same load and pressure, the length of the contact patch will be changing when going to a wider, or skinier, tire.

WIth a soft sided tire, like a drag slick for example, the width of contact patch varies widely based upon air pressure and load.

The same 26 x 11.50 tire might have a 9" long contact patch with only a width of 2" at 28 psi, but the same tire will have a 10" long contact patch with 3" at 18 psi. Then when launching and loaded as below the cotanc patch will grow much wider due to the load....
tt13.jpg


VS.

tt17.jpg
 
A contact patch is determined by load, not width. A narrow contact patch gives great directional stability, but a wide one means that a car will be able to change direction quickly and corner more quickly.
 
beeblebrox237
a contact patch is determined by load, not width. A narrow contact patch gives great directional stability, but a wide one means that a car will be able to change direction quickly and corner more quickly.
Click to expand...

really? A 195 tire has the same contact patch as a 315, i think not....
 
Beeblebrox237
A contact patch is determined by load, not width. A narrow contact patch gives great directional stability, but a wide one means that a car will be able to change direction quickly and corner more quickly.
Click to expand...

Not 100% correct as the Avon data in the OP's link clearly shows, increase in size doesn't scale 1:1 with load and you have the issues of sidewall deformation and that you can't infinitely increase the length of a contact patch (because sooner or later the rim is going to hit the ground.

Load and pressure are key factors in determining the size of the contact patch, but they are not the only ones.


1stlsx
Did u even bother reading the linked article?
Click to expand...

Please don't use text-speak - the AUP is quite clear on this
 
I understand now about the other factors involved, thanks guys! Where I got my initial thought from, was from a research and experiments thread here where the article was referenced. Also I meant to say deformation along the tread in my first post :D
 

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