Hey all, I recently installed Goodyear Duratracs (285/70/17) on the stock sport wheels and bought a flashcal to correct the speedometer. I followed the instructions and measured from the ground to the top of the tire and it came out to about 32". Uploaded the tire size into the jeep and the speedometer seems to be off a bit. It is dead on up to about 35-40 mph, but when you hit 50-60 mph the speedometer reads about 2mph faster than the GPS and is more noticeable at 70 (2-3mph). Any tips on getting the speedometer corrected from users that have the flashcal? Thanks

 

Try and make the size .1 bigger. If your speed is reading too fast your computer is reading your tire as being smaller than it is.

 

You can try as above stated or just leave it go. A few miles an hour is no big deal.


Sent from my iPhone using Tapatalk . Rich

 

I changed to 32.25, the next step up. We'll see if that corrects it. I probably should have done this from the start instead of making a thread. I'll blame it on being bored on a Sunday.

 

I had the same issue....with my 33's, I had to adjust my SuperChips to 31.50 to get my speedo to be accurate. It being off really effects the shift points.

 

I added 285 70 R17s duratracs ( went from stock Sahara 18" wheels and tires ) and have not needed to adjust anything. Speedo matches GPS dead on. I am assuming the GPS is reading speed from Gps and not tied to the speedometer.

 

Aren't those tires 11.5 inches wide? Did you need to do anything to accommodate that size tire?

 

[QUOTE="rob_engineer;4017188"] Aren't those tires 11.5 inches wide? Did you need to do anything to accommodate that size tire?[/QUOTE

I went with the AEV pintlers so there is enough back spacing as part of the rim. (I think). I also added a 2" spacer lift. The tires do stick out beyond the stock fenders a bit. I wonder if anyone else with this setup has speedometer issues. ?

 

In my experience the GPS speed and dash speedo are identical. When I make any kind of change with my Superchips Trail Dash, both readouts change and are always the same. I have compared this to a stand alone GPS and the readings are different. I have concluded that the in dash GPS (430N) receives it's speed input from the Jeep computer somehow.