lt1_fool

MPE, in 'theory' tire width/contact area has no effect on traction, and you summed it up with the equations :

(coeff. of friction) * (Normal force) = (Friction force)

(friction force per square unit) * (square units of surface area) = (Friction force)

When contact area goes up, friction force per unit area goes down, and friction force remains the same.

BUT

this doesn't take into affect shearing forces on the rubber. A larger contact patch causes less friction force per unit area, which means less shearing on the rubber. This shearing force causes the tire to deform and lose true contact with the road and/or lose rubber.

Tire composition and size of tread design are much better indicators of grip. Look at a standard truck tire vs a nitto or mt drag radial. The softer compound is obviously providing a better coefficient of friction, but the long/wide/short tread pattern 'strengthens' it, which helps to resist shear. A truck tire has short/narrow/tall tread patterns, which are great in the dirt, but horrible on the street. On a street with a decent surface, the tread will deform faster than anything.

Look at drag slicks. NO tread whatsoever. By the same theory, this would be the ultimate tire to resist shear, because theres effectively one continuous patch of rubber. Sure the compound is awesome as well, if you diced that up into small tall squares of tread, the shear would be so great that you'd prolly spin on those just as much as if you were on a set of wal-mart tires.

So now when someone says that "my 315's hook better than my 275's", they may or may not be right, but now you know why.

mpe488

The fact that formula one tires have wider tires, and better traction, does not defy any law of physics.

Have you ever heard correlation does not imply causation? If you've never taken stat, I'm sum this up for you: just because there is a correlation between tire width and traction doesn't mean the the tire width is causing better traction.

For example: it's possible that the softer compound causes better traction, but a tire constructed of that soft compound wouldn't be stable if the tire width was too small. So in order to use the soft compound the tire needs to be made wider. I'm not saying thats true, its only an example; but, you should realize that just because a wide tire has better traction it doesn't mean that the contact patch is responsible for the traction.

Again, I'm not claiming to have all the answers. If I did, I wouldn't be posting here looking for answers.

JMT-Z

This is from an automotive tire/wheel engineering forum.....
tire width

ONEBADASSWS6

Sometimes common sense can seem to defy the "laws of physics".

Wider tires, given the same tread compound and surface, will yield more traction. Simple as that.

Ari G

iTrader: (25)

Many cars have slappy suspension work but hook ok because of wide tires,wide tires are just band aid for slappy suspension work

Wider and heavyer tires have more friction force and allso when hot(softer),it increases

Wider and higher tires have more weight witch you don´t want,Taking 5 pound of the drivetrain is like taking 15 pounds of the car and it decreases the stress of the drivetrain,weight is critical

Many cars with 9" wider slicks are lifting the front end and gettin killer 60',it´s all in the weight transfer

Marc 85Z28

iTrader: (8)

Maybe I'm not following you... If a wider tire has better traction given equal variables, and it is not contact patch, then what is it?

THE_SUPRA

i think you are forgetting that the coeff. of friction is per object, the coef of friction on a 9.0" wide tire is less than the coeff. of friction on a 11.0"wide tire.


just think, if it didnt matter, then why would they have limited tire sizes in different classes of drag racing?

do you think a 10.5 tire class is slower than a 16.0 tire class because of the 5-6 difference in weight?

mpe488

unless your tires are made of the same rubber used in Formula one racing tires I'm going to go ahead and say its the compound, not the shape, that makes the difference.

lt1_fool

"A larger contact patch causes less friction force per unit area, which means less shearing on the rubber. This shearing force causes the tire to deform and lose true contact with the road and/or lose rubber."

Did anyone read my post? I'm pretty sure that sums up the 'missing link' which has been gone over in literally hundreds of articles and books.

lt1_fool

And if you believe in the 'compound, not the shape, that makes the difference' theory, why not run tires that are made of pure tar? That stuff is sticky as hell, but as we know, it doesn't hold up to any force at all, prolly wouldn't even keep it's shape if molded into a tire. Just because a tire is 'sticky' doesn't make it grip. It has to not only be sticky enough to take the force and not slip, it has to be strong enough to not break apart from the shear forces applied to it.

NHRATA01

iTrader: (10)

Absolutely, it all comes down to distributing the load. Its very easy to attempt to figure out frictional forces with equations, and taking the vehicle weight as the load at a point, instead of the more complex equations for a distributed load. Kind of like standing on a thin piece of ice on one tip toe, vs. lying down on it.

The more the load is distributed over a wider contact patch, the more force from inertia (ie turning, stopping) it will take to overcome the opposing frictional force of the tire to the pavement. Put your finger on a desk and press down, and try to move it. Now do the same with your entire palm. Similar scenario as far as contact patches go.

That's of course very basic explanations, assuming all is equal. Conversely, as it has been mentioned a wider tire doesn't always necessarily mean a larger contact patch, as a wider tire with a shorter sidewall can have the same contact area as a narrower tire with a taller sidewall. And then of course with a wider tire comes a heavier rim, which is more unsprung weight...tread compound effects...effect of road imperfections...etc, etc.

The easy answer is a wider tire with a larger contact patch should always have more grip, everything else completely equal (which is rarely the case).

MrDude_1

iTrader: (4)

id take a taller drag slick over a shorter wider slick (to a point)....
taller is more important then wider....(to an extent)

Cheatin' Chad

iTrader: (3)

The guy made points every bit if not more valid than yours and you reply with this?

You stated in a previous post:Even in the curves I dont beleive the wider tires help, the shorter sidewall does.




IF shorter sidewalls are superior to larger sidewalls then why do F1 cars not use rubber band sized sidewalls? I'll tell you why: Because for that application a relatively LARGER sidewall is better for handling. THIS is FACT. Ferrari spends upwards of 160million a year on testing. Both Bridgestone and Michelin have spent millions testing tires alone and they all have come to the conclusion that IN THIS APPLICATION a relatively larger sidewall is better for handling.

Due to this post your credibility on this topic is damaged. Please stop with the attacks and unfounded accusations. Merely spouting off equations and name dropping isn't going to impress anyone or give people answers.

Thank you.

THE_SUPRA

oh snap! if i were gay i would type "PWNED" here, but im not...so i wont.

wabmorgan

If wider tires don't help in the curves then why don't performance cars such as the vette and viper just run shorter sidewalls and not wider widths.

It is the extra width that helps. The short sidewall would help with quicker responsiveness of the car. Making the car more nimble. The shorter sidewall doesn't "slop" around as much making quicker, more responance turns.

At least that it my take on it. I can tell you is that I noticed a LARGE improvement when I went from stock to p285/35/18. (Of course, traction at take off got worse )


Of course, tire compound is also an important factor. So, yes you could have narrow tire have better traction than wide ones "if" the narrow ones had a soft compound vs hard compound on the wide tire.

A tall side wall helps traction in takes off due to the tire wrinkling up, like a drag tire does. This also explains why low profile tire have poor traction during take off. There is little side wall to give or wrinkle.

The wrinkle causes a larger contact patch and hence better traction at take off.

I would think that the improvement in traction seen in wider tires plateaues at a certain point. The question is at what point????

It surely is a trade off of one for another.

Manic Mechanic

iTrader: (3)

My take on this post was that he was talking about static traction, not dynamic. Launching a drag car and throwing a circut car into a curve are two very different measures of performance. But both stll reinforce my point which is, downforce is more important than width. That doesn't mean I believe width is irrelivent, rather it is not the most important factor in tire to surface adhesion.


I also agree with Mr. Dude. A taller tire of the same width will allow quicker acceleration from a dead stop as long as overall gearing is maintained. They will use more power though so MPH will suffer at the end. So it's still a balance.

Vernon

MadBill

Wow, some hot topic I just stumbled into!
There's definitely some good wheat amongst the chaff above, and the post by Knapp in the "Tire Width" link expertly covers the wide Vs. long contact patch issue (and explains why a tall tire/long patch is a plus for drag racing but not cornering), but there are a couple of other factors which have been omitted or touched only lightly upon:
o The classic F = N x mu friction applies to smooth hard surfaces and is only a part of a tire's grip.
o Mechanical interlocking ("hysteresis gearing") of the soft rubber with the track surface is a major factor.
o Molecular bonding of the tire to the track (think Post It Notes) is also significant, particularly on dry roads.
o The last two are temperature sensitive and a wider tire has more area to accept and dissipate heat, thus can be made softer without overheating.
o F1 uses tall sidewalls because they are limited to 15" wheel diameter. Prototype and Sports race cars generally use 18"-19" when rules permit.
o All else being equal, a wider tire will almost invariably corner faster, but may lap slower due to more inertia, higher rolling friction and or air drag.

slt200mph

iTrader: (42)

You forgot to inter the very important koolness factor into your equation..after all looking good or kool is very important..if the image that you want to portray is that of a 6 cly car then so be it..keep on running those shinny tires ... me I'll keep on running 275s in front and 315s in the back for the badass apearance package look..

Ericbigmac83

iTrader: (19)

I will give you that a softer compound will yield better traction over a harder compound with a wider tire. Throw all the formulas you want, but give me a larger contact patch anyday,thats why 315's are going on my car, not 245's

MrDude_1

iTrader: (4)

hint:
i'll take a contact patch thats an inch longer then one thats an inch wider, anyday.