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Today in my physics class we did a lab which proved that the area of contact is all that matters when optimizing the coefficient of friction. Just for the record, all 10 groups got the same results proving the same thing, and the other class got the same results, in fact the teacher has never had a group that found otherwise. Although, what did increase the coefficient of friction was the amount of weight. These results applied to both static and sliding friction. My question is...why the hell would any car benefit from wider tires?! It is obvious that they do, i'm not in any way shape or form trying to deny that every crew cheif and developer in F1, F3, WRC, NDRA, Nascar, SCCA has been wrong, actually it's quite the opposite, but how is it that more friction can be obtained if the contact patch doesn't matter?
 

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You are looking at this the wrong way. The contact area is the contact patch, the wider the tire, the greater the contact area. I thought that was pretty self explanatory. Our stock tires have a contact patch roughly the size of an average human palm, a wider tire will have more. The contact area you are using when determining the coefficient of friction would be the actual part of the tire touching the pavement. Get it now?
 

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The way we determined this, we meaning my peers and I, used a GSXR-600 and some concrete. We did a burnout, w/the bike braced in one spot, and measured the contact patch on his stock tire. Then we did the same thing after installing his new wider tire. Weight really isn't a signifigant factor when testing a bike that is slightly lifted off the ground but the area was wider. Not that this experiment is perfect but it gave us a general idea.
 

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one way also is to lift your car (on concrete) and wet the bottom of the tire with a sray bottle and lower it back down. Make sure you use the E-brake so the car doesn't roll.
 

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the dumbed-down, low-level physics formulas are right.

frictional force is only dependent upon net downward force, and the coefficient of friction, and contact patch DOESN'T matter...

but notice, they also say this only applies with mu is less than 1.

rubber has a coefficient of friction over one; it's one of the very few substances that does. some rubbers can approach a Cf of 4.

then the formulas change dramatically, and area of contact begins to matter.

i remember just having a thread like this recently... i guess everybody's high school physics class is getting to this topic right about now


edit: yep, found it
 

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a force on the surface that is perpendicular to the direction of friction (weight and gravity) has a direct relationship with the coefficient of friction. the area of the contact patch also has the same direct realtion ship in rubber, given that the surface mateiral is the same. the could be some experimental error in ur project where the scale of it was too small, making the results negligable. i assume that u did not exceed 10 lbs. but there is about 700 lbs on each tire in our cars, making a small percentage change of CoF much more significant.
 

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96dc2 on Feb/11/04 said:
According to this article, contact patch/area has to do with tire pressure and vehicle weight. Any thoughts on this?
i don't know if i'm answering your question in the right manner. lower psi = flatter tire = higher contact area, a heavier car produces the same effect...ever see dragster do a burn out? it spins the tire so fast that the contact patch decreases because the tire is both being inflated due to heat and because of the rotational forces being applied towards the normal of the surface of the tire.... grab a ball and a string and spin it...the faster you go...the more force it has towards the outside..meaning radially away from the center... same concept....
 

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Hakamoto on Feb/09/04 said:
The way we determined this, we meaning my peers and I, used a GSXR-600 and some concrete. We did a burnout, w/the bike braced in one spot, and measured the contact patch on his stock tire.
except if you were to do this with a car it wouldn't be accurate, because the contact patch at any given second on a car has to include the grooves in the tires. if you burnout, it's the contact patch disregarding grooves. which is also why professional racing doesn't have any grooves.

i'm not too sure about a bike. i know there are grooves on bike tires, but i was thinking they are not completely on the end of the tire, which is the part touching the ground when not turning.
 
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