Tire Profile Impact on Width

[North Coast Cab]

I've upgraded to a set of 7.5x17 and 8.5x17 wheels. I had been happily running 7/9x16 with 225/50 and 245/45 tires. I found the following calculator which is great for checking options in wheel and tire sizes, but it doesn't account for the impact by changing the width of wheel.
www.miata.net/garage/tirecalcold.html

Does anyone have another tool or chart?

Thanks, John

[Bill Verburg]

A useful rule of thumb is .1" increase in x-section per .5" increase in wheel eidth

You also need to account for loaded compression when performing dynamic calculations.

[North Coast Cab]

Thanks Bill. Another question I have is what the effect will be if I go with a lower, 40 series, profile tire upfront. Will this impact the over/under steer issues of the car. Trying to decide not just tire size options, but who's tire. Looking at MPSC or V700 225/45-17 & 255/40-17 or Toyo RA1 235/40-17 & 255/40-17. Fully adjustable sway bars will allow adjustment, but I don't want to pigeon hole myself with the wrong tire aspect ratio.

John

[Bill Verburg]

Toyo recommends an 8 - 9.5" wide wheel for the 235/40x17 Especially for performance use I wouldn't ignore that.


Even w/ the 225/45 and 255/40 your wheels are at the narrow end of the scale.