Is my speedo accurate?

Ok, heres the dealio...I got the edge tuner for my truck, not only for the kick *** power and engine managment system, but to calibrate my speedo for my 20" wheels wrapped in 33" mud grapplers and my 3:73 gears. I made a cutom tune in level 2 to correct the speedo, but I don't think it really did anything...is there any way to tell? It says Im going like 80 on the highway but Im next to people that Im sure are going about 70 tops! I didnt see any way to change the wheel size, only tire size and gears...am I over looking something? Thanks Guys

 

If you programmed your tire diameter to be 2632mm, use a lower number like 2575 to get the speedometer and Edge to clock slower. Check with a GPS or highway mile markers and adjust that last number programmed either higher or lower from previous.

Getting correct speed to indicate is a trial and error process with the Edge.

 

Find one of those roadside speed readout signs. That's what I ended up doing, turns out I'm doing 47 when the speedo reads 50, heh.

 

Get yourself a tape measure. Measure from the pavement to the TOP of the rear TIRE. You should have a number in decimal inches. (Like 31-3/8" = 31.375"). Forget the WHEEL size, it does not matter.


Get yourself a calculator. Do the following:

(Your TIRE height) X (3.1415) X (25.4) = NUMBER TO PUT IN EDGE FOR TIRE SIZE.

If your tire is 33 & 1/4" tall, then:

(33.25) x (3.1415) x (25.4) = 2653 This is the number to put in the EDGE for tire size.

Mine is dead on at 60 mph.

 

Ok, thanks for the help guys, Im going to try something after work.

 

The best way is with a GPS. I thought mine was way fast. Checked with a GPS and it was only 2 mph fast.