This is probably a ridiculous question for most to read, but I am changing from a stock tire to 35" Pro Comps. What can I expect as far as the speedo and odometer accuracy? Will I actually be putting more miles on the truck and be travelling quicker than what the speedo reflects?

 

Your speedo will read slower and your odometer will rack up less miles

 

I believe that the percentage change in tire height would also be the percentage of error on the speedo. i.e. if your new combo is 10% different in height your speedo will be off 10% as well.

http://www.discounttire.com/dtcs/infoTireMath.dos

 

Thank you guys very much

 

Buy a new speedo gear. VERY VERY VERY easy to change out.

One nut and the whole assembly pulls out. Pull off the C-clamp in the gear, slide the new one and bam. Corrected speedo.

Where I bought mine:
http://www.transmissioncenter.net/sp...n_______va.htm

 

Interesting related topic....
When I had my stock rims and tires, my speedo was 3-4 MPH faster than my GPS was reading. I don't know about anyone else, but I would trust the speed on the GPS before I would the ODO. When I went up slightly in tire diameter, the two are now reading within 0.1 to 0.3 MPH difference of each other. Go figure.

 

I went up about 1.5 inches over stock and when I go by those radar traps that display your speed it seems to match what my speedo says. I wonder if my stock calibration was off.

On changing the speedo gear, didn't they switch to an electronic system around 1999? I guess once they made the change you have to buy a programmer for like $125.

 

Yea in 99 they switched to electronic. But look at the top right of his post:

Vehicle:1997 F150

 

Ah missed that. Seeing as most people here have newer I figured he probably did too.

I have a '98 and think the 97-03 styles still are the best.