Speedometer error

[oldyellr]

My son just got a set of alloy 15" wheels with 30" off-road style tires for his 1998 2wd Ranger that came with 14" wheels. I figure his speedometer would be reading 13% slow, so he'll actually have to stay within the posted speed limits to be safe. Can the computer be reprogrammed on these trucks to correct the speedometer and what's needed? He's have to do this twice a year when switching between summer and winter tires.

 

[RonD]

1998 uses the GEM(generic electronics module) to correct for tire size

Info here: http://www.explorerforum.com/forums...ule-reconfiguration-computer-flashing.134477/

You will need the revolutions per mile if you get that far

Inflate tires to YOUR normal level.
Put a chalk mark on the lower side of the tire and on the ground next to the mark on the tire, roll truck forward or backwards so tire goes around 1 time then put another mark on the ground
Measure distance between the two Ground marks
Say it was 7.5ft
Divide 5,280ft(1 mile) by 7.5ft = 704 revolutions per mile

There are also charts for that

 

[pjtoledo]

get a GPS device/APP and determine the actual error amount.
you will probably find the MPH and odometer have different error rates.
then do the GEM adjustment with tweaking as needed.

 

[oldyellr]

Okay, thanks. I knew there had to be a way. Just too expensive for the tools or having a shop do this twice a year.

 

[RonD]

You could use a universal speedometer interface

Like this one: http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=126/prd126.htm

There are a couple of companies that make these

This would allow you to correct speedometer signal as needed for tire size changes