BigE_2003

i have a 88 nissan kingcab, 2wd, auto with the 3.0 litre. i want to get new tires and rims for it, i was wondering if i change the total diameter of the tire/rim combo that the speedo will be wrong, or can the computer automatically compensate for this, cuz i know on some vehicles it does, and if it doesnt, is there any way i get reprogram the computer to fix the speedo change?

jadcock

Yes, if you put on tires of a different overall diameter, your speedometer will be off. The computer has no way of knowing what size tire you have on your rear axle. In fact, for a vehicle that old, I bet it's a mechanical speedometer. The calibration for that is a particular gear at the base of the speedometer cable, where it plugs into the transmission. Trucks that came with different sized tires from the factory than yours would have a different gear in there. I personally wouldn't bother with trying to correct the speedometer unless it would be off more than 10% (if your new tires are 10% taller or shorter). Not worth the effort (to me).

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Jason Adcock
Always Tread Lightly!
1995 4x4 XE King Cab - 189,000 miles
1997 Cadillac Seville - 141,000 miles

1997XETruck

Here's a pretty decent calculator for seeing how much error you'll introduce.

http://www.paspeedo.com/calculator.htm

Heath

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1997 Nissan XE Truck - 133,000 Miles
1990 Infiniti Q45 - 91,000 Miles
2005 Infiniti G35 Sedan - 34,000 Miles