So I've got the new 35's on and I haven't had my speedo calibrated. Does that mean I'm going slower than it says? If so does that mean it's registering more miles than I'm really going? My MPG has gone down about .5mpg but to be honest I don't know if that's because the odometer is off. TIA

 

i dont remember what size the stock tires are off hand. i put 275/65R17 in a calculator, and used the tires in your sig. came up with vehicle speed of 71.876 w/ speedo reading 65, and when vehicle speed is 65, speedo read 58.782.

and yes you need it recalibrated. computers (mainly ABS) still think you have stock tires.

 

Crap... I was hoping to get by without getting it recalibrated. Any idea on how much something like that runs and who would do it?

 

the speedo counts rotations of the wheels through the transmission. for each rotation of the tires, the speedo adds a set certain distance to your odometer. a larger tire diameter rolls a longer distance for each rotation, so your speedo will see that as going slower than you really are, and covering less distance. i know bf goodrich has a tool for figuring this out on their website, i'm sure you can find a few others by searching around.

 

Stock TRX4 tires are 275/70/17. Your dealer can fix your speedometer reading. They should do it cheap or free if you have a good relationship with them. When I put 305/70/17 Wrangler MT/R's on my 03 off road ram i went back and they did it for free.

 

How long should it take? Should I set an appointment or just drive up?

 

They did mine when I had it in for an oil change. I would call them. If it's like the dealers around here, they are not very busy right now.

 

Thanks guys..will do.

 

If you want to see the speedometer / odometer changes made by a specific tire size change, try one of the online calculators:
DML Tire and Wheel Calculator

 

I heard that if they reflash though that you'll need to get it adjusted again?

I was just planning on waiting for the Superchips programmer...