My speedometer reads incorrectly in my '97 F150 XL, due to it having 265/75-R16 tires instead of the stock 235 series tire. Is there a way to figure out how much variation exists other than having a deputy clock me with his radar? Also, is there a way to recalibrate the speedo to play nicely with the different tire size? Thanks

 

http://www.miata.net/garage/tirecalc.html

That site says your speedo is off by 9.3 percent now. When your speedo says 60, your really going 65.6 Might as well say 10 percent, easy to do the math when your going down the road then, close enough

You can take it to a Ford dealer and have it reprogrammed for 265/70/17 tires. Its practically the same height as yours. Cost is around 80 bucks I think. Or else get a chip/programmer that you can use to change tire size. Superlift makes a thing call "TruSpeed" too that will adjust it.

 

I just noticed you have a 97, so a programmer and such wont work for the speedo, you will need a new VSS gear with the correct number of teeth.

 

Thanks for the reply, I'll probably just do the math on the fly instead of screwing with trying to find the correct gear.

 

the gear is really cheap, like 10 to 15 bucks, and takes like 2 seconds to change. you can get it at a dealership. if your truck is fourwheel drive it is just in the side of the transfer case and held in with like one nut.

 

Not sure how accurate they are:

http://www.oly4x4.com/4x4calculators.htm

 

Take out the VSS gear you have now and count the # of teeth on it. It's probably 20. Then get one with one less tooth on it. That should sync up your speedo/odo.... How do it know.... Well, I did the same thing!

You will want to get the VSS fixed, because if you haven't already noticed, your tranny shifts at different speeds now because it thinks it's going slower then it really is.

Anyway, once I got mine fixed it drove much better and having the speedo/odo calibrated means you don't have to lie when you sell the truck and have to state that the # of miles on the truck is accurate... (you are putting on less miles on the odo with the stock VSS gear...)

Mitch