My speedo is off...how do i fix it

[ivorton74]

I got pulled over today in my truck..i was doing 55 mph but the cop said i was actually doin 63 mph...i didnt believe him so he showed me the radar gun and it was 63. So i got my gps and went for a run and it reads correct until i get past 20mph and then its all wrong...for example when the speedo reads 35 the gps says im doing 42. Im running stock size tires 235 75 15...so how do i correct my speedo? Now i have to drive with my gps....im just glad i just got off with a warning...i dont want to get no tickets for this.
Posted via Mobile Device