Bob Cosby

No doubt tires with more contact patch will result in less mph by the end of the 1/4 mile. It becomes a trade-off, and usually a good one, as you spend much more time in the first 10 ft of a track than the last 10 ft.

PacerX

This is not correct.

The assumption here is that pressure is being held equal, which it should not be.

Xilant

If this is true why does the Z06 have 19" with 305? What you just said doesn't make any sense at all.

Xilant

I already did explain this on the first page. They keep the same overall tire diameter regardless of rim diameter. Therefore how can a rim with a larger diameter possibly give off more traction???

Traction is tire on pavement. The wider the tire the more rubber touching the road's surface and thus more traction. END OF STORY.

JakeRobb

Increased tire diameter can give more traction, by increasing the length (front to back) of the contact patch.

Increased wheel diameter is irrelevant to the size of the contact patch, but is not irrelevant to the amount of available traction. Have you ever seen a wrinkle-wall slick? On tires like that, a larger wheel would hinder the tire's ability to do its job. On regular street tires, the same effect is in place; just to a much less obvious degree.

It's not the end of the story.

For a given tire diameter, going wider shortens the length of the contact patch. Looking only at the most basic physics, it appears the total amount of rubber touching the road's surface does not change (the size of the contact patch should vary only with vehicle weight and tire pressure). That's what HAZ-Matt was saying, and he was claiming that because of that, there is no inherent traction advantage to a wider tire.

In practice, it's much more complicated than that. Everybody knows that all other things being equal, a wider tire gives more traction. As it turns out, both the shape and size of the contact patch change. See the link bossco provided above for the details.

Xilant

Yes, I know and understand this. A tire that has a physically wider diameter does have more road surface. HOWEVER, going form a 20" to 21" inch rim does NOT change the tire's overall circumference. While the 20" is 245/45ZR20 and the 21" is 245/40ZR21. Both tire's circumference are the SAME so you don't get any more traction!

Anyways, I know I'm right and it's useless for me to waste any more time in this thread.

2010_5thgen

wow. good run. im sure theres alot of excuses that the mustang guys will make for that run. i told everyone it would be a close race. numbers or no numbers. the ss is a competator to the gt500.

STOCK1SC

Can someone sidebar this tire width pissing match?

JakeRobb

You're wrong.

The tire's circumference doesn't change, but due to the sidewall flex issue I mentioned, the amount of traction does.

HAZ-Matt

That is more or less what I was saying.

Hmmm so I might have completely wasted everyone's time if we are drawing this conclusion...

Sure, this is what everyone "knows" Sort of like everyone "knows" that cross drilled brake rotors are better for braking (except for people that actually race their cars). The problem is really that whenever someone upgrades to a wider tire they usually end up with either a softer compound or a more aggressive tread pattern or both just like practically everyone that upgrades to drilled rotors changes their brake pads to a more aggressive compound.

Yes. Apparently for slip and shear the dimension that is in the direction of the slip or shear is more important than the dimension perpendicular with regard to traction... which is partly why a wider tire helps cornering. The shortening of the contact patch and reduced sidewall deformation, if you are keeping pressure and compound constant, decrease forward traction (although it reduces rolling resistance at the expense of air resistance). In real life I agree that switching from X tire at 235 tread width to something in 275 tread width may end up giving you better straight line traction but it is despite the added width and not because of it. Since they can get similar treadwear (or even give it up in a performance tire) by going to a softer compound and they could reduce the absolute sidewall strength due to the lower aspect ratio you may end up ahead.

Just as some people on the board like to correct grammar (when 99% of the board doesn't care) I like to harp on wide tires for straight-line and even more so on cross drilled brake rotors.

Now back to GT500 v SS.

HAZ-Matt

I know I said I would stop but...
!!!!!
No it is IMPOSSIBLE if it has the same tire pressure as the narrower one. The shape has changed, not the area.


And I have no idea what PacerX is getting at. Are you supposed to drop the pressure in the tire when you go up a size? I suppose you could... I haven't read any recommendation about that... could someone PM me a link to a source if it exists so we don't waste more of this thread?
Actually if the compound and pressure is the same you probably get less straight line traction from the 21" even if the footprint is the same because the lower aspect ratio tends to reduce sidewall flex which hurts straight-line traction especially from a dig.

Ok I promise to be quiet about tires now.

Xilant

You're right, I didn't take into account for sidewall flex.