How do I recalibrate the speedometer after the PO installed larger tires?? I checked on Dakota Digital site, but I didn't find anything about recalibrating speedometers. I pretty sure the speedometer is at least 5 mph off or more around 65 mph.

 

http://www.sonoransteel.com/speedo.html

 

Thanks for the info. Now I just have to get the sensor ordered and find a place that calibrate the speedo.

 

All you need is a piece of highway with mile markers and a stopwatch. Drive at a consatnt speed, and time your truck over 1 mile, or 5 or 10 for more accuracy. Calculate your actual speed, compare it to your indicated speed and program the digital thingy accordingly. Should be close enough.

If you have a GPS you can also use that.

 

Not trying to dig up an old thread, but there's a handy speed calculator for those who may only do tire swaps. It's listed here at a Miata website:
http://www.miata.net/garage/tirecalc.html

I hope it can remove some confusion/frustration and save time for those who add the unit to their truck. I know I'd like to be sure if smokey pulls me over.

 

How big are the tires? I have +1 (265/75) on mine and at 70 it reads about 2-3mph faster which is right for the size of tire. Under speeds of 50mph the speed diff is negligible. I used the marker method and I drove by a few of those speed limit radar thingys on the side of the road a few times.