[harryevan]

I've got a 2000 Astro AWD and ever since I bought it used 3 years ago the speedo has been running 10% fast - it reads 82 at 75. I've checked it against 4 different cars and trucks on the interstate - cell phones DO have a use. I've also noticed the same amonut of error on the different "your speed is" radar signs and trailers around town - 10% fast.

My tires are P215/70R15's all around instead of the reccomended P215/75R15's (seems the tires shops all agree on this after 3 sets) which accounts for a 3.1% difference in circumference (miata.net). I contacted a local Chevy dealer about adjusting the speedo and they said it's an hour - $95.00. When I asked if this included checking to see if the correct sending gear is in it and they said "why?"

So, can a 10% adjustment be made through the onboard computer, or should I ask a (different) Mr. Goodwrench to check the gear and adjust it?

harryevan