Speedometer question.

[IS300E30]

The problem with the theory if I put the correct tire size on my car then the speedometer will read correctly. I

s that my OBC is accurate as if I set my OBC to beep at 70mph then when my gps says 70mph the car beeps because the OBC is accurate but the speedometer will read 80mph when the OBC is set for 70 and beeps.

What gives?

[nando]

the needle on your gauge could have been moved? 10mph is quite far off, mine is about 4-5mph.

[Bimmerbear]

only one I've seen:
http://www.e30tech.com/forum/showthread.php?t=73541

I don't have the capability to do that electronic stuff, so could I use a guess and check method with the potentiometer to calibrate the speedometer? I picked up my e30 today and the speedometer reads about 10-15 mph higher than my actual speed.

[Curt Hayes]

Not saying this is your problem, but my speedo read a consistent 5mph high, so I pulled the needle off and moved it back 5. I found two in a row that were the same, so I fixed them both.