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OP
OP
- Thread starter
- #17
The difference between stock tire size and new tire size puts my speedo reading 6-7mph slower than actual speed, a 9%-10% error is a big enough difference for me to want to correct. Helps me avoid any unscheduled interactions with the fine men and women of Law Enforcement.
I am double checking the GPS speed reading with a couple of street mounted speed limit signs on my commute that have real-time speed displayed. Pretty confident I can get the adjustment done as accurately as possible without putting the Bronco on a dyno. GPS speed in a straight line with a clear view of the sky is supposed to be 99% accurate. I can live with a 1% discrepancy.
I did a similar calibration technique on my Harley after I installed an aftermarket transmission (Zippers Zip-Rack with back cut gears). The main drive gear on that was larger than stock, I had to shim the speedo sensor up a bit to accommodate the larger gear, and 'cause the gear had a different number of teeth than the stock main gear, I had to permanently hardwire in a speedo calibration device under the seat. The Hall-Effect speedo sensor basically counts the teeth on that gear as it spins to calculate speed. I mounted a motorcycle GPS unit on the handlebars, drove past the speed displays, and pressed some buttons till everything matched up.
