Tire geometry

[sammm]

Can one of you pointy-head types break this down for me? Looking at 3 different sizes of rear tires.

• 315/30/18
• 295/35/18
• 275/35/18

What would be their characteristics or what would make one choice better than the other? Thanks!

[creek]

The 315/30/18 would be horrible on the street in my opinion, not enough sidewall and you will go through aluminum rims regularly unless you go forged. The 295/35/18 has the highest sidewall at 4.1 inches and will give the best ride and rim protection, it's also the tallest tire and should help gas mileage due to highest "gearing" 772 revolutions per mile. My 2 cents says comfort and rim protection is worth losing 3/4 inch in width on 12" wide tires.

[sammm]

Thanks creek. I should have mentioned these would be strictly AX tires. Not for the street.

[jrj512]

What does it matter? You'll get whichever is cheapest.

[sammm]

Comparison using a Tire Calculator

[POS Racing]

What is the stock size?

[Nails]

Wider gives more lateral traction vs. linear traction. Area of the contact patch remains the same for all sizes so I'm guessing the lateral traction is more desirable than linear for AX.

[POS Racing]

Wider gives more lateral traction vs. linear traction. Area of the contact patch remains the same for all sizes so I'm guessing the lateral traction is more desirable than linear for AX.

But then what affect would larger rear tires with more lateral grip have on the smaller front tires? Could you could change the entire balance of the car by just playing with the width of the rear tires??

[wrx74]

Linke or Linke

[Nails]

You're talking about staggering the tires and yes that would be different than the usual setups for miatas. I think that wider rear tires would tend to push narrower front tires causing an understeer. But I'm just guessing here since I've never staggered tires on a Miata nor have I AX'ed one for that matter. So I'm purely hypothesizing.

[Titus]

You're talking about staggering the tires and yes that would be different than the usual setups for miatas. I think that wider rear tires would tend to push narrower front tires causing an understeer. But I'm just guessing here since I've never staggered tires on a Miata nor have I AX'ed one for that matter. So I'm purely hypothesizing.

Sammm replaced his Miata with a Z06.

[sammm]

What is the stock size?

Stock sizes are -
front: P265/40ZR-17
rear: P295/35ZR-18

[altiain]

Several missing variables:

• Width of the rear wheels
• Width of the front wheels
• Expected front tire size
• 1st gear, 2nd gear, and rear end gearing (i.e., what will max speed be in 1st & 2nd with each tire size?)

[altiain]

You're talking about staggering the tires and yes that would be different than the usual setups for miatas. I think that wider rear tires would tend to push narrower front tires causing an understeer. But I'm just guessing here since I've never staggered tires on a Miata nor have I AX'ed one for that matter. So I'm purely hypothesizing.

While Mazda tends to set up it's rear-drive cars with uniform wheel and tire sizes, most other manufacturers do not. The stock Z06 is designed around staggered tire sizes, so Miata/Mazda specific experience isn't really going to apply.

[sammm]

Several missing variables:

• Width of the rear wheels
• Width of the front wheels
• Expected front tire size
• 1st gear, 2nd gear, and rear end gearing (i.e., what will max speed be in 1st & 2nd with each tire size?)

• 18x10.5 rear
• 17x9.5 front
• Front tire size - 275/40/17
• ?

[ken o]

275/40R17 98W

BLK

W

98

200 A A

610

$146


295/40R18 103W

BLK

W

103

200 A A

625

$235

Qty.

OR

315/30R18 98W

BLK

W

98

200 A A

622

$303

Qty.

I like 275 front, 315 rear. But since you are TCB the 295 are $68 cheaper. BTW DT will match the price.

[ken o]

Also important is setting the ride height. Dropping the front will make the rear very loose. I think you can drop the rear then balance the handling with the front height.

[altiain]

• 18x10.5 rear
• 17x9.5 front
• Front tire size - 275/40/17
• ?

3 out of 4 ain't bad, but you missed the critical one. Back to school, young grasshopper.

[sammm]

Also important is setting the ride height. Dropping the front will make the rear very loose. I think you can drop the rear then balance the handling with the front height.

I've read that lowering on stock bolts while still running OEM shocks (which I am for now) is not good. It will bottom out on the bump stops.

[CosmosMpower]

3 out of 4 ain't bad, but you missed the critical one. Back to school, young grasshopper.

Think C5Z06 FD is 3.42. Not like that car really needs a gearing advantage with all that torque on street tires anyway. He's already going to have a heck of a time trying to put down 75% of the torque to some Falkens or whatever tire he picks.

I'd get the widest rubber you can cram on the rear tire so probably the 315/30.