What are everyone's thoughts for this situation? My speedometer is 6 mph fast, but my odometer is clicking off miles just as it should!

I've seen the speed difference through my phone's GPS, a stand alone Garmin GPS and even all the construction speed signs that are all over Pennsylvania.

At first I thought it was the tires but the odometer would be off too, right? Just in case it helps I have the USP 18's with 235/40's and a set of 16's with Bridgestone blizzaks, same 6 mph on both sets.

Any ideas are appreciated, and any DIY fixes are fantastic!

 

I'd be interested in a fix, too. My wife's Avant's speedometer is about 3-4 mph fast. So when she thinks she's driving at the posted 30 mph around town, she's really only doing 26-27, and people are getting pissed at her for driving like a granny.

 

My '02 1.8TQM seems to be 2 or so MPH fast, too, and I'm on stock 16" wheels with the stock 215-55R16 tire size. I think there's just some error in any speedo, but 6 MPH off like the OP's seems too much...