Straight line grip vs width

[wildcatgoal]

To this day I've gotten my best consistent 0-60 times with Conti DWS tires. Haha.

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[ahl395]

Cool, thanks. I was hoping to stay with 19s though. I'll have to consider it, but I have 3.15 gears and that is a tall tire.

Sorry I was just pulling numbers out of the air lol. I've found, owning two sets of 19s, that the tire size choices are not the best.

They do make Pilot A/S in 325/30/19 though. :cheers:

 

[Grintch]

A wider tire will have a larger contact patch with the road

Nope. As noted above, changing the tire size alone just changes the shape of the contact patch. Run 35 psi in your tires, and the contact patch is the same size regardless of tire size.

Side note - wider patches (from wider tires) give better cornering grip. Longer patches (from taller tires) gives better acceleration and braking traction. For a visual example of this compare the profile of a F1 cars tires to a Top Fuel cars tires.

 

[ahl395]

Nope. As noted above, changing the tire size alone just changes the shape of the contact patch. Run 35 psi in your tires, and the contact patch is the same size regardless of tire size.

Side note - wider patches (from wider tires) give better cornering grip. Longer patches (from taller tires) gives better acceleration and braking traction. For a visual example of this compare the profile of a F1 cars tires to a Top Fuel cars tires.

So you're telling me at 35psi a 235 width tire and a 325 tire will have the same contact patch, and the 235 will give better acceleration traction?

 

[BmacIL]

So you're telling me at 35psi a 235 width tire and a 325 tire will have the same contact patch, and the 235 will give better acceleration traction?

The first part is definitely true.

The second can be true, but depends heavily on tire and setup. If the % of tread groove (basically voided area that doesn't touch the ground ever) relative to tread width is the same between the two, then yes. Since with most tires that's not going to be the case, a wider tire will still have more grip. Also in practice, sidewall stiffness plays a role and a narrower tire has its sidewalls closer together, making for a 'stiffer' tire in normal load conditions.

The point is: going wider and doing nothing else different will nowhere near net you the benefits you're looking for (straight line grip), or that it's capable of. To truly take advantage of that extra width you need to drop your pressures.

 

[Bartly]

Haha, I must have swapped from square to staggered to square to staggered 100 times in the last month. Now I’m back at square, or maybe staggered, lol.

 

[Grintch]

So you're telling me at 35psi a 235 width tire and a 325 tire will have the same contact patch, and the 235 will give better acceleration traction?

All else being equal, yes.

How big is the contact patch? The math is car weight/load (lbs) / tire pressure (lbs/ square in) = area (square in)

No factor for tire width, height diameter, etc.

Of course, everything else is never equal. And a bigger/wider tire should see less stress than a smaller one, so in theory you should be able to lower the pressure (and increase the contact patch) or use a softer compound thus increasing grip.

 

[ahl395]

The first part is definitely true.

The second can be true, but depends heavily on tire and setup. If the % of tread groove (basically voided area that doesn't touch the ground ever) relative to tread width is the same between the two, then yes. Since with most tires that's not going to be the case, a wider tire will still have more grip. Also in practice, sidewall stiffness plays a role and a narrower tire has its sidewalls closer together, making for a 'stiffer' tire in normal load conditions.

The point is: going wider and doing nothing else different will nowhere near net you the benefits you're looking for (straight line grip), or that it's capable of. To truly take advantage of that extra width you need to drop your pressures.

All else being equal, yes.

How big is the contact patch? The math is car weight/load (lbs) / tire pressure (lbs/ square in) = area (square in)

No factor for tire width, height diameter, etc.

Of course, everything else is never equal. And a bigger/wider tire should see less stress than a smaller one, so in theory you should be able to lower the pressure (and increase the contact patch) or use a softer compound thus increasing grip.

Interesting, good to know. I do run a lower pressure in my 305s versus my 285s so I guess that makes sense. :cheers:

 

[ZenkaiRacer]

How about the contact patch of a thin spare tire vs a 325?? Lol

 

[Grintch]

How about the contact patch of a thin spare tire vs a 325?? Lol

Compact Spare tires run high pressures to make the small tire carry the weight of a full size tire. So yes, they have a smaller contact patch (because higher pressure).

They also have a hard compound.

I know this is counter intuitive, and everyone hates the idea. But A - do the math, math doesn't lie.
B - this is based on everything else being equal, and everything is almost never equal.

PS - I fit the largest wheels and tires I can, but I also pay attention to my pressures. Especially at the track. Supespension setup is not as simple as just fitting big tires, using stiff springs, and lowering the car as much as possible.

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