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Car Forum / Ford / Ford Trucks / November 2007Speedometer Calibration
I bought a "97 F150 that the PO had fitted with 265/75x16s. This tire size works out to be roughly equivelent to a 32 x 10.50, where the factory fitment is closer to a 30 x 9.50. My problem is that when the speedo reads 60-ish, my actual speed is more like 70. The error is rather large, and it goes in a direction that exposes me ot speeding tickets -- if I set the speedo according to the signs, my actual speed exceeds the setting. How is the speedo calibrated on my truck? On my '81 Jeep, I can pull a gear and swap it. Will my Ford truck be handled the same way? >I bought a "97 F150 that the PO had fitted with 265/75x16s. This tire size >works out to be roughly equivelent to a 32 x 10.50, where the factory [quoted text clipped - 7 lines] >How is the speedo calibrated on my truck? On my '81 Jeep, I can pull a gear >and swap it. Will my Ford truck be handled the same way? The '97 uses a sensor in the differential. It picks up on a ring the rotates with the ring gear. The only thing that will change the accuracy of the speedometer is the tires diameter.. The PCM has to be reprogrammed to account for the error. It can only be calibrated 6 times IIRC. I do not know if this can be don't outside a dealer facility but, I would be suprised if that is the case. There is no gear or mechanical device that an owner can change. Someone here may know a way around this Lugnut >>I bought a "97 F150 that the PO had fitted with 265/75x16s. This tire size >>works out to be roughly equivelent to a 32 x 10.50, where the factory [quoted text clipped - 21 lines] > > Lugnut Superlift makes the TruSpeed Speedometer Calibrator which changes the electronic signal between the sensor and the ECM to correct the speedometer reading. The nice thing about it is you can change back to a flip of the switch (like if you swap tires often) and you can fine-tune it if you have a GPS. Go to the dealer and you still might be 5-10% off. >>> I bought a "97 F150 that the PO had fitted with 265/75x16s. This tire size >>> works out to be roughly equivelent to a 32 x 10.50, where the factory [quoted text clipped - 27 lines] > switch (like if you swap tires often) and you can fine-tune it if you have a > GPS. Go to the dealer and you still might be 5-10% off. 97 is not computer controlled. It has a VSS gear in the transmission. Not sure which gear you will need. 99 and above are computer controlled. For more info, go to www.f150online.com and search for "VSS gear". >>>> I bought a "97 F150 that the PO had fitted with 265/75x16s. This tire >>>> size [quoted text clipped - 33 lines] > sure which gear you will need. 99 and above are computer controlled. > For more info, go to www.f150online.com and search for "VSS gear". It may use a gear but it still produces a signal for the PCM and ECM, as opposed to a direct mechanical linkage to the speedo. Superlift Tru Speed model number for a 97 is 33001. > >I bought a "97 F150 that the PO had fitted with 265/75x16s. This tire size > >works out to be roughly equivelent to a 32 x 10.50, where the factory [quoted text clipped - 19 lines] > > Lugnut So my first question would be around the size of the stock tires for that vehicle? It sounds like a previous owner may have up-sized the tires and remembered to difference so they could avoid a visit from a police type. Then the original poster gets to decide whether they need to go back to original tire size or pony up to recalibrate the sensor. Or what? H. > So my first question would be around the size of the stock tires for > that vehicle? It sounds like a previous owner may have up-sized the [quoted text clipped - 7 lines] > > H. You are correct, the PO installed oversize tires, and now I have to either compensate or pay-up for the recalibration, or return to the factory tire size. On my Jeep, I can buy a gear for a few bucks and drop it in, but on my Ford the speed pick-up is done differently, and it seems that the truck has to be re-educated. Perhaps the fine folks over at 4WheelParts can make the adjustment ...
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