Is there someway to calibrate the speedometer or at least check it? I have been checking the speedometer against one of those signpost radar units. My other car is within 1mph, but the Blazer is way off....the speedo is showing faster than what the radar speed display shows.
Now I put larger diameter tires on, but I though this would cause the speedo to indicate a slower speed than actual....but it appears to be the opposite.

I have not check the odometer against highway mile markers yet.

So again, any way to check speedometer calibration?

Thanks.

 

I checked mine against my GPS when I went to 30's
was pretty close

BTW I think bigger tire diameter will make you go faster than the speedometer reads

 

Easiest and most accurate way to check the speedometer and odometer is like Rex mentioned, with a GPS. And yes, larger tires will indicate slower than actual because they rotate at a slower speed, (less PPM, pulses per mile, as measured at the VSS). The PCM can be recalibrated using a Tech2 scan tool.

 

the tinfoil hate wearers will say its so your warranty goes up faster on your truck. but ive noticed that in every car/truck ive owned and anyones i drive past those radar things im always going like 2mph faster on my speedo then the radar is stating

 

Every manufacturer has a +/- margin of error in their speedo programming. It's better if yours read high rather than low.

 

if you have a smart phone i use an app called Ulysse Speedometer

one of my fav apps just cause its actually useful lol