bigger tires, speedometer calibration?

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Feb 4, 2008 | 10:54 PM

metal13x

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bigger tires, speedometer calibration?

I just upgraded the tires on my 97 f150 2wd from the stock 235/70/R16 to 255/70/R16 (new 16 inch wheels). Though it is not a big difference and it is something I could live with, it would be nice to have my speedometer accurate. Does anyone know where I could find an adapter for my speedometer for a slight speed difference, or do they only make adapters for bigger differences in tire applications (usually seen with big 31, 35, 40 inch tires)? Also, are they easy to install/uninstall if i use my old stock wheels/tires?

Feb 5, 2008 | 04:00 AM

fdrf150

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When I got larger tires on my truck 285/70/17 I had the dealer calibrate it for me when I went in for an oil change. They did it for free but I'm sure not all dealers are the same. Other than that I believe the tuners such as a Predator or Supertuner would do the same.

Feb 5, 2008 | 06:40 AM

Joe Finn

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From: DC

I'm pretty sure a '97 uses "gears" not the PCM for speedo control. You should have no problem getting your speedo right because 255-70-16 was an optional size from the factory. Got 'em on my truck.

Feb 5, 2008 | 11:14 AM

metal13x

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is a speedometer gear easy to locate and install? I know we replaced a speedo gear in our jeep and it was fairly easy

Feb 6, 2008 | 01:02 PM

tim.moman

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From: Olathe, KS

the auto tranny and the transfer case use the same spedo gears. Do a search including 4wds and you will find quite a bit of info

Feb 6, 2008 | 01:13 PM

galaxie641

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From: SE Wyoming

Yep, you need a new VSS (Vehicle speed sensor) gear. But that is such a little difference it wouldn't be worth messing with to me. You are looking at a 4% difference.