Join Date: Apr 2010
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Complete How To Set Speedo
Since there is really nothing on the net about how to set the speedo, here it goes.
My specific speedo was factory set with all switches on 0 (including the last one, as mine is in kms, Canada eh?)
Next to the switches is the factory setting sticker. Here you will notice that along with the 10 positions for the speedo, but also the settings for the rest of switch 2. What i have learned is that on switch 2, numbers 4-6 switches is for teeth/rev. At first i was not sure what this was for. Basically, if you put in a custom setting for pulses/mile, you HAVE to have these switches to the correct factory position, which in my case is 4=0, 5=1 and 6=1. If you dont flip these switches, your speedo will NOT work as well as the rpm will NOT work. Also, if you dont flip the correct ones, rpm may not work at all or show the incorrect rpm's.
Here is the calculation i used:
I measured the tire diameter from concrete up. Get as accurate of a reading as you can get. My 10r22.5 are 39.5 inches.
Calculate circumference which is 39.5 * 3.14 = 124.03 (3.14 is a constant for all)
Calculate circumference in feet 124.03 / 12 = 10.3358 feet.
Calculate total revs/mile at the tire 5280 / 10.3358 = 510.8458. (5280 feet per mile is also a constant for all)
Calculate pulses/mile at the drive shaft 510.8458 * 4.44 (axle ratio) = 2268
Cross reference that with the chart for the dip switch settings. Use this as a starting point. If your speedo is measuring too fast, try a higher number like 2300, and if the speedo is measuring too slow, try 2200 as a reference point.