I had the dealership lift my truck and swap the stock tires for BFG 285/65/20 KO2's. They recalibrated it to a tire size (unknown) that was close. I am being told that they can only pick sizes in the software that are available and evidently this size isn't. I am about 5 mph off at 65mph. They said the only way to fix that is with a tuner. I am sure I am not the only one with this issue. Any feedback would be greatly appreciated.

 

Hopefully they swapped the size to a stock F250-F350 20" tire size. They run 275/65 which is a 34.1" tall tire. You are running a 34.6" tall tire. But who knows if they can access that size or not.

What are you using to check your speed?

 

Interested as well.

 

I used a Hypertech Speedometer Calibrator, after a couple tries the correct size to get dialed in was 33" w/ BFG KO2's 285/65/20 on stock rims. Sizes went in .25" increments.

https://www.f150forum.com/f118/uscsi...2/#post4372042

 

what are you guys using to check to speed with? GPS? Is that reliable?

 

In what software? Ford's IDS software will not calibrate the speedometer on a 2015. They must be using aftermarket if they did it.

 

What size tires were on there factory?

I feel like they didn't do anything if you're still off 5mph at 65mph. My tires are 34.8" and I'm only ~7% off. That makes me about 5mph off at 70mph.

 

I have used GPS and the road construction radar and they both jive. So evidently, they can't do anything at the dealership.......

 

"they can't do anything at the dealership.......", good thing we have this forum :thumbs:

The techs and service advisors usually end up using Google to do a search and most likely end up reading through these forum threads. At least that was my experience when I asked them to turn off the engine noise enhancement.

 

The dealerships are not allowed to set to a specific tire size, only tire sizes that Ford installs on their trucks. Now 15 years ago, the system was flexible and you could put down a chalk line and measure the diameter and they could set the size, if yours was not one of the multiple sizes listed. Nowadays you have to set it with a speedometer recalibration device.