Here's a link to a great tire size calculator that takes all the guess work out of the effects of oversizing tires.

I spoke with a memeber today, monahan-z, and as a result I now understand that Lambo has a electronic traction system as does Ferrari. So, tire sizing is important.

This calculator can tell you everything that an oversize tire will do to speed, etc.

I use it constantly.

See: http://www.miata.net/garage/tirecalc.html

I have also excel sheets of Michelin PS/2 and Michelin Cup tires if wanted. They will not post here, unfortunately.

Nice Link...