Got my math right?
 

Just trying to see if I have my math right... I just bought a set of Honda VX wheels and was going to buy tires for them. Since the 165/70-13's seem to be fairly limited, I was thinking about going with the Kumho Solus KR21's in a 155/80-13, but the plus seems to be the 155/80-13's are about a close to stock size as I could get anyway.

So for the math...

STOCK SIZE (1995 Civic DX sedan)

175/70-13 would leave a 175*.70=122.5mm sidewall. Wheel diameter is 13in or 330.2mm. Total tire diameter would be 122.5*2+330.2=575.2mm.

NEW TIRE SIZE (on VX wheels)

155/80-13 would leave a 155*.80=124.0mm sidewall. Total tire diameter would be 124.0*2+330.2=578.2mm.

That is a difference of 578.2/575.2-1=0.52%

So at a speedometer reading of 70mph my car will actually be going 70*1.0052=70.37mph.

Does that all look correct? Just trying to make sure I actually know how fast I am going and how far off my MPG calculations might be.

So yes....

Depending on how accurate you want your speedometer, if you went up a couple sizes to something like a 185/80/13 you would probably be able to get a litte better mileage because of the taller gearing, but you'd need to verify the larger tires were not going to create any rubbing issues.

Well then speedo and odometer would be off and I would have to do more calculations on my fuel economy to get "actual fuel economy"... lol I am too lazy for all that. Will probably just go with the 155/80-13, especially since tires are almost half as much.