Was cleaning my new(-ish) F-Type S Coupe last night and whilst doing the wheels noted the tyre sizes. I have the 20" Tornado rims and see that the fronts are shod 35/255 and the rears 30/295. The fact that the rears are massively wider than the fronts doesn't require reading of the numbers on the sidewalls or explanation, of course but why do the fronts have taller tyres? Doesn't this make the front wheels larger (in a diametric sense) than the fronts? Why is this desirable?

 

That's not how it works; on a typical tire (P295/30/20), it is the treadwidth in mm, the height as a percentage of treadwidth and then the rim size.

35% of 255mm = 89.25mm height

30% of 295mm = 88.5mm height......close enough to be considered the same


Dave

 

Well, you learn something every day. Thank you very much.

 

It is about the only thing in the world that is represented by three completely different units of measure: mm, percent, inches

 

No problem. :-)

Cheers,
Dave

 

Yep; very strange when you think about it.....still easier than the old system though; Tire Size Helper

Dave

 

+1. Before the hybrid metric/English sizing, you couldn't calculate anything without tables . Now with simple multiplication and addition, it's simple to get a close approximation on most of the tire dimensions.