Gas Mileage Affected?

[Spyder]

not true....

If you compensate the tire size you can have accurate readings....

Time to go back to schoool!!

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

That is correct, unfortunatly not very often does it work out to have the size tire they recommend on a car... its all about maintaining the proper circumfirence. however this only helps the speedo and odo... the gas mileage and hangling will be affected reguardless because of a change in the placement of weight... and the fact you just added a ton of unsprung weight.

[speedminded]

^^^^ What they said basically. You always want to keep as close to the original outside diameter as you can. You go up a wheel size then you go down a series in tires.

hey bert, enter the before and after info in this calculator and post up the results... http://www.miata.net/garage/tirecalc.html