Speedometer recalibration

[Leford]

Who knows how can I recalibrate my speedometer?
My Explorer is a 92 Sport manual Tranny.
It had 255.70R15 tires. A few months ago I put on my X new tires 31x10.5R15 and I know that my speedometer lies to me

 

[Alec]

You'll need a speedo gear one tooth smaller than your current one. Takes about 5 minutes to change; write-up in the tips section of the site.