Tire size & speedometer reading ??

[Pakrat]

I just went from 265 to 295 tires. Is this going to make the speedometer show faster or slower ?? I never can remember!! Also is there a way to correct the speed showing- new gear or something. Thanks all !! See you in Portland on the 14th. Larry

 

[Valkyrie99]

The speedo will read slower. I have 275s and according to my GPS, I am 7 mph slower than I am actually going.

 

[Valkyrie99]

There is an encoder on the rear differential. It can be reprogrammed but only goes up so high. (If that is the correct term) Mine has already been set to the largest. I have to live with the error.

 

[work2muchplay2little]

Just bought one of these for my truck to correct for the taller tires: http://www.abbott-tach.com/era.htm. See this thread also if you have 4 wheel ABS https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=18843 I bought mine directly from Abbott

 

[SLang]

Our trucks have OBD II in them since 97. I have not been in the Dodge system, but the Chevy and Fords allow for tire size corrections. I have a friend that works for a dealer and used their machine to talk to the computer in my Chevy. Try asking your dealer to use their machine or barrow it for an evening.



Also Summit use to have a recalibrator box that went in line with you speedo signal. Just turn the knob and dial it in.