Ok, so I went from the stock suspension with 265/75-16 wheels to a BDS 4" front leaf, 3" rear block lift, Billstein front/rear shocks, and BDS dual front steering stabilizers, with 295/75-16 wheels on my 2003 F250 6.0 Lariat.

My next question is this:

Until I get my speedo adjusted, will the meter read faster or slower than actual speed?

And finally, someone told me that my 2003 F250 Lariat's speedo is computer controlled, not gear controlled. Can I adjust this myself? If so, what's the best way?

Thanks
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Your speedometer will be a little slow. In my case, I went from a stock 265/75R17 to a 285/75R17 tire, which is about 1 inch taller. When my speedometer reads 57 MPH, my GPS says I am doing 60 MPH.

Yes, the speedometer is computer controlled. There is a sensor on top of the rear differential called the VSS, which feeds a pulsed signal to the computer and is used to determine the speed. You can adjust the speed using a programmer. You will need to enter the revolutions per mile of your new tire to make it correct.

Doing this may help your truck in other ways, since the shifting and ABS also take information from the VSS.

 

Awesome, thanks for the input. It didn't even dawn on me about how my tranny shifts.

 

With 315/75-16's, my speedo and odo read about 10% low. 55 mph indicated is actually about 60 to 61.
On the '99's, it appears to be impossible to adjust the speedo with a programmer. I am not sure when it became possible to do so, but later models can be adusted.

 

I corrected the speedometer on my '99 with AE.
https://docs.google.com/viewer?a=v&p...hmNTYwODNiYTUx