A Tire Question

[DANNOV]

My 2003 Boxster S has 17" Bridgestone SO2-A tires. The fronts are 205/50 on a 7" rim and are listed as having a diameter of 25.2". The rears are 255/40 on an 8.5" rim and have a diameter of 24.8". I have done a lot of track miles and my fronts are worn.

I am considering changing to Michelin Pilot Sport PS2 tires. I intend to install 225/45x17 on the front and 255/40x17 on the rear. The Michelin 225/40 has a listed tire diameter of 25" and the 255/40 is also at 25". All of these diameters are from the spec section on the TireRack website.

As you can see this change will lower the front of my car by .2" and raise the rear by .2". That does not sound like much but in my experience, often even small changes are noticeable. Has anyone done this, and is the increased rake noticeable? Will it affect handling on the track? Any opinions on the Michelins?

[KevinC]

I wouldn't worry about that at all. First of all, it's the radius of the tire that directly determines the height, not the diameter. So, you are really talking about 0.1", not 0.2". This is small compared to the tread depth and won't be noticeable.

[DANNOV]

I wouldn't worry about that at all. First of all, it's the radius of the tire that directly determines the height, not the diameter. So, you are really talking about 0.1", not 0.2". This is small compared to the tread depth and won't be noticeable.

My error, you are right, it is the radius that determines height. The change is so small that it probably does not matter. Thanks for the reply.