on my 94 that i bought the speedometer says that im doin 10 miles more than wat i actually am (ex:if im going 50 the speedometer says 60) anyone know wats goin on?

 

How do you know your true speed?

 

well i got my mom to get behind me and i called her and asked her how fast she was goin and she said 50. well i looked on my speedometer and it said 60 and she was drivin right on my tail

 

what tires are you running.

 

That was my next question but they would have to be REALLY tiny to give a 20% error like that.

 

im runnin 265/75/16 cooper discoverer ATR right now. and i dont know wat yal consider really tiny but they look tiny on my truck but i bought the truck with the tires on it and just havent changed em yet

 

I could be the tires especially if the truck is lifted. It can put a strain on the Speedo box and set the gears off....best way to test speed more accurately is the go past one of them signs that radars your speed in construction areas or school zones...we have those here in WV.......i bet you are not 10mph off....but closer to 5 or 6....

I saw your other post too....going from 16in to 15in rims will make a difference too on the speedo.....

 

hes running the stock size tire. That wouldnt throw his speedo off that much. Rims, yes, but still not that much.

 

Ok, Lucy, you got some 'splainin' to do ... how will rims affect speedometer error?

Good idea to use the road radar.

 

It throws the computer reading off....different rim size...different sping the the wheel....the damn computer is finely calculated to read any lil change even down to tire pressure....which can affect the speedo...

Or so i have been told....