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I bought a jeep with very small tires (not sure the exact size). I recently bought a new pair of tires that are probably 2 or 3 inches larger radius. Do I have to update my jeep so the speed is calibrated for the larger circumference of the tires?

Edit: sorry for the confusion, but I bought four new tires.

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If you posted the exact model of Jeep, it's pretty easy to look up the exact size of tires you really need. –  Bob Cross Dec 24 '12 at 15:07

2 Answers 2

Yes. That is a significant difference so your speedo will be out by a lot.

In some regions it is required by law to have an accurate speedo!

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Depending on the age of your Jeep the recalibration involves either swapping speedo drive gears in the tranny or reprograming the computer. The reasons for having this done are that modern vehicles use many data points for different systems and they all interconnect at some point. ABS, transmission shiftpoints,traction control, cruise control are all looking for accurate vehicle speed data. Not to mention blackbox data in the event of a serious accident.

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