speedometer and odometer off

At an average speed of 50mph, a 2mph error is 4% Along with tire wear, etc. Probably all related.

 

Speedometer running slow 1 to 2 mph would also cause your odometer to be running LESS miles than actually travelled. If one is running slow and the other running fast there's a problem somewhere other than tire calibration.

My new T680 came with steer tires on all 10 positions. We took them off the drives and put on lugs which are quite a bit larger diameter than the tires that came on it. The result, at 70 mph indicated I was running 73 per calibrated GPS. For every 100 miles I drove per the odometer I actually traveled 105 or 5% more so the odometer and speedometer were both slow (again checked against an aircraft calibrated GPS system). I just went in Saturday morning and changed the RPM in the ABS system for the drives (which also stopped the random ABS light when turning right) because this truck uses the signal from the left rear ABS tone ring for the speedometer/odometer. I reset the trip in my GPS and checked it against the odometer coming to where I'm at now and for 208.8 miles I had a difference of 1/10 of a mile between the odo and GPS. Speed was exactly matched on both.

If you have a speedometer reading slow and an odometer reading fast then you have much bigger problems than tire sizes.

 

I have a 2007 volvo vn. My odometer says I'm going 85 while a GPS says I'm only doing 69 yes truck is governed. I changed the transmission speed sensor and it still does the same. Also my mileage is way off. When I travel a certain highway i know for fact is 250 miles from state line to Stateline. It is actually saying I've done 305 miles. That's 55 miles over. What else could be the problem. Please help !!!!!!

 

It’s most likely a wrong setting in the ecm. Find someone that can read and make changes to the ecm.

 

OK I will.try to find someone to do that. Also the cruise doesn't work because the speed I assume . However if I'm in idle I can set cruise to idle up. Butvif I'm going down highway it shows its on. But it will not set.