buying some rims and the tires are 305 25 19 in rear and fear they maybe like riding on rocks.... is this just to low profile a tire for the 997 that will be driven on normal new england roads (roads kind of stink around here -boston area- in general) ? I don't mind a stiff ride but wife will drive car from time to time... The car will also be getting techart coil overs...

any advise greatly appreacited....

RUF wheel 19's 8.5 fronts and 11 rears offset is 56 for front and 70 rear..... what kind of spacer sizing am I going to need for a 997 narrowbody car for these to sit perfect flush with fenders or am I going to need spacers with lugs attached?

 

i have gone through a few wheels with and without spacers and feel that 49-52 is good for the rear if you want it to be flush on an 11in wheel with 305's.
i think the oems are 57 in front so you probably should go to 50 or so...

 

I think we use a 7mm spacer for that wheel.

 

well, 7 will get you to 63mm which is more aggressive than the 67 that comes from the factory especially with the extra 5mm from the 305 tires (which puts you at 58mm compare to the 67mm wheels and the 295 tires), but still you are not anywhere near being flush with the fender...

 

There is a 1" difference (3.7%) in the diameter between 305/25 and 295/30 .. This might be an issue for the internal computer.

 

This will help explain it all: www.miata.net/garage/tirecalc.html

I just went from 295/30/19 to 315/25/20 and I can tell no difference. And, my speedo now only reads one mph high instead of the two mph high factory setting. I checked it by GPS.