speedo gear??

speedo gear??

Ok, now remember I have played alot of hockey and been hit in the head several times. I don't quite understand how/what I need to measure. "side wall thickness"? for example.:-k Remember keep the explanations simple:hockey:
This is the example from Jack's link.

Tire Size: 245/60/15

245mm/25.4mm = 9.64 Inches Section Width

9.64 in. X 60% = 5.79 in. Side Wall Thickness

5.79 in. X 2 = 11.57 in. Total Side wall height

11.57 in. + 15 in. (Rim Size) = 26.6 in. Diameter

So with this Tire Size and 3.91 Gears, I would use a 40 Tooth Speedometer gear.

Thanks