Im not looking for how I can fix the spedo difference with the tires. Basically Im just looking for other people on here who put 31" tires on and if they know the difference between what the speedometer says and what theyre actually doing. I did search and didnt find anything other than how to correct the problem so I apologize if this has allready been brought up. And its a 2002 chevy Blazer 4x4. Old tires were 235/75/R15 and the new ones are 31/15/10.5

 

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

You'll have to convert inches to mm but you can use it. Also, physically measure the 31's. Some tires are actually shorter than what they advertise.

 

thanks a lot. worked perfectly

 

I dealer can fix that for you or anyone with a Tech II or equivalent scanner. Since 31s where a stock size for the ZR2's.

 

By my calculations, speed would be understated by about 13%. But if someone has realworld experience, I would depend on their advice over my calculations.

 

I'm off 8 with 32's

 

It depends on how fast you are going so it would have to be a percent and 8% seems a little low.

 

well I used to just cruise with the traffic but today I got pulled over for doing 50 in a 35. I told the officer about my speedo problem so he only wrote me a ticket for a faulty speedometer but I think im just going to drive along side someone I know and have them go exactly 35 so I know for sure.

 

It only really seems to be noticeable (for me anyway) above 60. Of course my sidewall is only 5% taller than stock (235/75's instead of stock 235/70's) so when I'm going 60 on the speedometer I'm actually going 63 and change. The more you deviate from your stock size the more drastic the difference will be. I don't think it's possible your speedometer showed 35 and you were actually doing 50, that's quite a gap!

 

my blazer had 215/70/15s and i'm now with 31x10.50x15 and according to the website mine is off 14.1% slow 8 mph at 60mph. when i'm driving around the city i do the posted speed limit accroding to my odometer and havnt got pulled over knock on wood lol. guess i should slow down a little bit.