Compression Ignition Addict
Join Date: Mar 2007
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Picked up the truck yesterday afternoon. Turns out I had to pay 51 bucks and change (after tax) to have them re-calibrate the cpu to take into account the new tires.
Prior to the change, my speed was off by about 2.5 MPH at 60MPH (calculated by GPS). After the adjustment, I am still of by at least 1.5MPH or more. SO, in my opinion, his is very little improvement for my 50 bucks. Had I known that this adjustment would only bring my spedo 1MPH closer to being accurate, I probably wouldn't have spent the money.
For future reference here's the tech write-up indicating what the lower limit of the module is in our '08 vehicles:
26210 TIRE SIZE REPROGRAMMING PROGRAMMED TIRE RPM TO 596, THE LOWEST ALLOWABLE BY MODULE
For reference, my 35's say that the revs per mile is 593. Close, but no cigar