We were coming home from the races yesterday and I had 2 buddies following. Had the cruise set at 79 per the Edge and 82 per the speedo. I called one of the guys following and asked how fast he was going and he says 70. He even checked it with his GPS. It's a 06 FX4 I bought used and I think it had the factory BFG tires on it. 275 18s. Why would it be off by 9 mph? Can the dealer flash it to fix it?

 

If you have an Edge, set it yourself. You need to makes sure it has the correct setting for your tires and especially check your gears. Do you know if it has the original gears? if so, see if the Edge default is the same ratio that you actually have.

 

I set the tire size by what the Edge manual says. Don't have it with me at work right now and I don't remember what that number was. 2557 or something like that. Should have the original gears. I bought it from the original owner who only used it as his weekend truck. I talked to him and he never mentioned changing gears.

 

See what gear ID is on the door label. Compare that with the Edge default.

 

Are your tires 265/65/18?

 

275/65/18. 3.73 limited slip. 2559 was the actual number I input for the tire size.

 

Ok, first thing I would do is go into the Edge settings and select "save Previous Settings" and hit enter. Then go to gears and see what it reads. If it reads 3.73, then I would physically check my driveshaft. Get the truck on stands wher you can turn the wheels one full rotation. Mark the driveshaft and see if it makes 3.73 turns per each tire rotation. If it is closer to 3 1/2, you have 3.55s.

Also, I would change the tire setting to 2431 and try that. The manual does not allow for squish and the 2431 allows for 5%. But that can not account for you being off that much. I would think it has to be in the gear setting.

 

Would a VIN number help? 1FTPW14VX6FA71141

 

Nope. If the Edge is recognizing a 3.73 in your PCM and your door tag says 3.73, you need to physically verify that you have a 3.73.

 

Here's a stupid question. Does the Edge adjust the truck speedo also?

 

Yes. The Edge changes the setting in the PCM, any device recording the speed will be adjusted. The truck speedo is nearly always 2-3 mph fast at highway speeds. That is a mechanical difference that is built in.