Speedometer Adjustment?

[jgriffin1988]

My speedometer runs 5-10 mph fast, is there any adjustment that can be done? I am running 265/75R16 tires. The truck is traveling slower than the speedometer reads. This is a problem at interstate speeds. Please advise.

[C2500]

Originally Posted by jgriffin1988

My speedometer runs 5-10 mph fast, is there any adjustment that can be done? I am running 265/75R16 tires. The truck is traveling slower than the speedometer reads. This is a problem at interstate speeds. Please advise.

You didn't say what year your truck is but there is a calibration kit that has the clip with pins that is installed in the dash cluster. You cut off the correct pins that correspond to the axle ratio and tire size. The chevy dealer should be able to show you the correct pin configuration.
Harry

[rpreston]

jgriffin, unless i'm reading your post wrong, with larger tires than stock (taller), your speedo should be reading SLOWER than your actual speed. I have 285's on my 90' now and the speedo reads about 5 to 6 mph lower when I'm really doing 55. In other words, when I'm doing 55, the speedo reads 49 to 50 mph. Maybe there could be something else wrong?

[Rbraczyk]

I have the same problem as jgriffin. Methinks the mileage and age got to the truck and the wheel speed sensors aren't working like they used to.

[jgriffin1988]

Originally Posted by rpreston

jgriffin, unless i'm reading your post wrong, with larger tires than stock (taller), your speedo should be reading SLOWER than your actual speed. I have 285's on my 90' now and the speedo reads about 5 to 6 mph lower when I'm really doing 55. In other words, when I'm doing 55, the speedo reads 49 to 50 mph. Maybe there could be something else wrong?

Thanks for the info, my tires do have substantial wear but they're factory-original size--265/75R16. I think you may have mistaken the sizing format for tires, I believe it's given as width/height/rim diameter, where the width is in millimeters. The rim size is of course in inches....Why they have mixed units of measurement is beyond me. Anyway, I'm replacing the rear tires with new Michelin XC LT4's, the front tires have already been replaced and are new. I will see what effect new tires have on my speedo and report back here. R/, James...