Tire Size not Changing

[Longshot270]

The easiest way I have found to get the tire size accurate with a GPS is to set your tire size to something you know is wrong, like 2400, clear the odometer on your truck and on the GPS, drive 10 miles then input the numbers as shown.

(GPS Miles/Truck miles) X 2400 = New Tire Size

[ak_cowboy]

So I started at 2573 with my gears of 4.10 and was showing 51mph while travelling 55. Shut the truck down, loaded previous settings, and changed the TS to 2774, speedo didn't change. Loaded previous settings again, upped TS to 2900 and speedometer was still off by 9%....

[Jackpine]

Originally Posted by ak_cowboy

So I started at 2573 with my gears of 4.10 and was showing 51mph while travelling 55. Shut the truck down, loaded previous settings, and changed the TS to 2774, speedo didn't change. Loaded previous settings again, upped TS to 2900 and speedometer was still off by 9%....

OK, do it again. This time, tell me what your Tire Size value is right after you "Load Previous Settings" (before you enter anything new). Also, if you DO have 4.10 gears installed, tell me what the Gryphon shows for Gear Ratio after the "Load Previous Settings" step.

If you're doing things right, you should see a TS value that is "close" to 2900 and a GR that is 4.10 at this point. Tell me what you find and we'll go from there.

- Jack

[ak_cowboy]

My TS says 2905 and GR is 4.10. My truck has the heavy duty package and came stock with 4.10s.

[Jackpine]

Well, that surprised me. The TS and GR are definitely stored in your "customized" tune file. This leaves only ONE possibility, you are not loading them into the PCM.

So, do it again, for whatever tune you want to use. Scroll to "Load Previous Settings". Check the TS and GR if you'd like, hitting [Enter] after viewing each setting, then scroll to "Done" and hit [Enter]. At this point, you should see the usual progress display telling you that the PCM is being programmed. At the end of this, there should be a "click" under the dash and a "programming complete" message (as I recall).

A TS of 2905 should make your Gryphon and dash speedo read MUCH faster than the GPS. I would think that would show a +9 mph error at a true speed of 70.

And, if you've followed my directions exactly and still have the same problem, I'm out of ideas - except what year is your truck? I've been working on the assumption it is an 04-08 model. Is it possibly a pre 99 model? If so, you cannot adjust the speed with a programmer. You will need to change the VSS on the rear axle if you mount non OEM tires. Edit: Nevermind - I see from your User Profile that you have a 2007 truck.

- Jack

[ak_cowboy]

I'll give it one more shot, but I dont' have much hope either lol This is a first gen Edge and I've never been able to change the tire size since I got it.

[Jackpine]

Originally Posted by ak_cowboy

I'll give it one more shot, but I dont' have much hope either lol This is a first gen Edge and I've never been able to change the tire size since I got it.

Have you checked for any firmware updates? To do so, return your truck to stock, then start Pegasus on your PC. With Pegasus running, plug in the Gryphon. Click on [Updates]->[Gryphon Update Manager] and apply any firmware and calibration updates you find. Then, click on [Updates]->[Custom File Download] to reinstall your custom tunes. After that, try reloading your tune with an adjusted TS. You MAY need to adjust the GR too - the updates may wipe out your "Previous Settings".

- Jack