Gearing and MPH

[Jorley]

I hope I've got this in the right forum. I know nothing about rear end gearing and was wondering if changing it would affect MPH. According to the door sticker my Bll came stock with 195/75R15, I put 31x10.5R15 on it and the speedo is 5 mph slow according to gps(55=60). I checked a tire size calculator and it showed it should be 60=51.3. Could someone have changed the gearing before i got it and how could I find out.

http://www.1010tires.com/tiresizecalculator.asp

 

[Hahnsb2]

I hope I've got this in the right forum. I know nothing about rear end gearing and was wondering if changing it would affect MPH. According to the door sticker my Bll came stock with 195/75R15, I put 31x10.5R15 on it and the speedo is 5 mph slow according to gps(55=60). I checked a tire size calculator and it showed it should be 60=51.3. Could someone have changed the gearing before i got it and how could I find out.

http://www.1010tires.com/tiresizecalculator.asp

It's probably because your tires dont measure out to 31", mine tape 1.5" short...

 

[pillen140]

thats because your tires affect your gearing also. your bigger tire takes longer to spin one complete turn. you can go with the next higher number gear (ex. 3.45 to 3.73) or change the speedometer gear on the end of the speedo cable.

 

[MAKG]

Well, yeah, you can change the differential gearing to compensate for an incorrect speedometer, but it's a $500 ($1000 for a 4WD) solution for a $20 problem.

Just change the speedometer drivegear.