My 2021 F-150 came stock with some pretty wimpy Michelin 275/65-18 (32.1" diameter) and I came across a deal on some new take-offs with some better looking General 275/70-18 (33.2" diameter).

I take it that my truck should be re-programmed for these larger diameter tires. I assume the only way to get this done is to have the dealer re-program the truck for these larger tires. What are most of you paying to have the dealer take care of this?

 

Most people are making the change with forscan or a tuner.
Are you sure General 275/65-18 are 1.1" taller than Michelin 275/65-18 ?

 

I also changed to a 33" tire (285/70/17) and read in a couple spots on the 14th gen forum that the truck automatically adjusts to different tire size by comparing the OEM programming to the GPS/navigation speed. Is this true? Does a relatively small change in tire size (32" to 33") require Forscan or tuner reprogramming? My speedo seems very accurate when driving by radar speed signs/trailers, so I guess I've assumed my truck figured it out. Would be nice if someone can confirm if the truck auto adjusts or if a manual reprogram is necessary. Thanks!

 

What is "forscan" and how much does it cost?

275mm = 10.826"

65% of 10.826" = 7.03"; 7.03" X 2 = 14.07"; 14.07" + 18" = 32.1"
70% of 10.826" = 7.57"; 7.03" X 2 = 15.15"; 15.15" + 18" = 33.2"

My original post had the wrong aspect ratio for the Generals; it should have been 70.

 

I would refer to both tire manufacturers' for the revs per mile as a comparison, based on some things I've seen.

Forscan has a free version which requires you to update the code every couple months if you keep making changes over time, you can get the OBD2 connector for around $30 or so depending which one you go with. You would need a laptop to plug it into. There are guides on how to make the programming changes for tire size. Make sure you follow the instructions to save a copy of the stock configuration.

 

Funny you call the factory tires 'whimpy'.
Those tires are about the size I upsized my old truck to (1993 F150). haha

Kidding though, but the new tires are still fairly whimpy at just an inch taller.
At 3% taller, it will probably take more time to fiddle with getting the size dialed in than it's worth.

With that said, if you do go for it, using FORScan, you'll find more items to fiddle with too. There are stickies for each of the model year designs to read through.


Also, I've never ever head of a vehicle self-calibrating for different tire sizes. If the new trucks do that, Ford is sure putting a lot of faith in their GPS supplier. That would be a 100% accurate speed as the tires wear out.
This thread is the first time I have read that thought. I'm not in the 2021 forum on purpose however if a thread title is intriguing, I read it regardless of what subcategory it falls under.

 

OK, so I finally upgraded from the stock chrome wheels with 275/65-18 (32.1" diameter) Michelin Primacy XC tires to 265/70-18 (32.6" diameter) General Grabber tires. And I went to the Ford dealer and asked them to re-program the truck for these new (slightly) taller tires. The Ford dealer stated that they can't do that as there is no way to re-program the 2021+ F150 for different tire diameters.

Anyone know how I could properly calibrate my F150 for these slightly taller tires???

OLD:


NEW:

 

You can get a hand held tuner thingy (I don't know which one(s)), or FORScan.
However, trying to dial in the 1/2" change is going to be a lot of unnecessary time.
It's only 1.6% larger which is difficult to dial in. Your speed differential at highway speeds won't even be noticeable.

If you wish to dive in though, get familiar with FORScan.

 

I did a speedometer check, against the GPS, with my taller 265/70-18 (32.6" verus 32.1"diameter) tires. And the speedometer was spot on.

Since Ford no longer gives the dealer the tools to re-program for different diameters, I wonder if the truck uses the on-board GPS to recalibrate for different diameters???

 

They usually set the speedo fast. Your size difference isn't that much and probably why it is spot on now. These trucks do not self-reprogram. I have 275/65R20 and reprogrammed mine with FORSCAN. Correct your speedometer error - no flash or tune required | 2015+ S550 Mustang Forum (GT, EcoBoost, GT350, GT500, Bullitt, Mach 1) - Mustang6G.com