Putting what sounds like a tire question here because I am actually curious about what defines specific OEM equipment as it relates to Super Dutys, as well as the general tire question. In two parts:

Part I:
Truck is a 2021 F-250 7.3 XLT 4x4. No tire or wheel was package was ordered. The OEMs are the ContiTracs in LT 275/65 R18 123 120S E as listed on window sticker and build sheet. Almost every fitment guide online shows those specs for their OEM replacement when shopping.

However, I came across one (maybe two) that show this is the OEM replacement:
LT275/70R18 E 125/122S.

BigO is one of them. Have they simply incorrectly loaded an optional tire spec as the standard? Do PSD equipped trucks have a different OEM tire when all else is equal? (That makes no sense since payload already accommodates the extra weight, but who knows.)

On their fitment calculator, if I select the actual OEM tire, it returns "Load Range/Index does not meet requirements for a 2021 Ford F-250 Super Duty XLT".

Part II:
Have you personally replaced your LT 275/65 R18 with a LT275/70R18? The latter are an inch taller and will throw off speedo by 3%. How difficult is that to correct if I dig up my FORSCAN and get it to work, which will actually be a bit of a hassle. Do tire shops do that these days? I tow fairly heavy and the truck is already rough as can be, so I would not mind moving to the higher load index except that 3% discrepancy might **** me off.

Thanks.

 

LT275/70R18 is the standard tire size forced option with FX4 package. Lots of truck owners go up in tire size, and supposedly the forscan tire size change is easy, but most tire shops are not going to change forscan tire settings.

 

LT275/70R18 is also a selectable independent tire option when building the truck, and I know it comes on some packages, but regardless of FX4 or not, it's not the standard size and I am surprised it is listed by a few places as the default.

The problem with FORSCAN is it is a pain for me to do even simple tasks because no windows machine and i need to use an emulator and i will need to find my OBD reader and "yadda yadda yadda". Didn't figure most places would change tire settings ... but they do it for TPMS when needed so ....

 

On the FTE forscan spreadsheet, there is a list by location of members willing to do forscan changes for you.

 

Yes, on 4x4 trucks, 275/70/18 is an optional size tire.
I went up from the 275/65's to 275/70's and have not changed my speedo setting, it runs just under 2 MPH slow at 70.

 

I've had 2 gas F250's and a diesel F250, all 4wd and all came stock with 275/65R18 Conti tires. I hated the tires and swapped all the trucks to 275/65R20, stock take offs I found locally from higher trim package trucks. This obviously creates a speedo discrepancy which I have not fixed on any of the trucks. Trucks have all run fine with the taller tire/wheel combo (about 2" taller). The taller tires I've noticed are also load index 126 where as the stock Conti's were 123.

 

Makes sense.

As far as the conti's, I am surprised I have eeked 35,000 out of 3 of them. One was replaced under warranty because it never balanced properly. Not good tires. The Super Duty front end seems to really chew those tires up, even balanced and aligned. I do almost all towing and I would have thought the rears would be the wear tires - not the case.

I am also trying to keep wheel size the same because my fifth wheel clearance and leveling right now is just where I want it. No need to add another headache. I got a truck with 18's intentionally, so not going to change that now.

 

Wheel diameter makes no difference, it is tire diameter, you can get tires for 20" wheels the same diameter as the ones for 18's, and IIRC, the oem 20's are the same diameter as the 275/70/18's.

 

Of course the overall tire diameter is what matters.

I would be surprised if the OEM 20s are the same total diameter as my OEM 18s and i am not going to look it up at this point since it is not relevant to my discussion since i am not getting new wheels. ... but they could be I suppose......

edit, i could not help looking it up. OEM 20s are 2" larger diameter than my OEM 18s, as one would expect:

275/65R18 (My OEM tire)
Diameter : 32.1"
Width : 10.8"
Wheel : 18" x 7.5-9.5"
(LT Tires 7.5-9")
Sidewall : 7.0"
Circum. : 100.7"
Revs/Mile : 629

275/65R20 (OEM 20 on a current Lariat built from Ford.com)
Diameter : 34.1"
Width : 10.8"
Wheel : 20" x 7.5-9.5"
Sidewall : 7.0"
Circum. : 107.0"
Revs/Mile : 592

 

I went up from 65 to 70 due to finding a set of take offs. Makes the truck look much better. It only makes the truck 1/2” taller.

I’ve got 3.31 gears on my 6.7. Towed 14000 lbs over the Appalachian’s without issue.

 

My '22 6.7 F350 came with 275/70/18.
Forscan is pretty handy. You could buy a used laptop off Craigslist for $30 and use it just for Forscan.

 

Do like I did and buy you a super cheap windows laptop just for FORScan. I'm an Apple guy and wanted nothing Windows on my Mac.

Or, you can contact ARod from Powerstroke Tech Talk on YouTube. He's a Master Ford tech and he can do FORScan mods for you by remote access.

 

I went one step further yet. My truck came on 275/65-18 tires and as soon as I confirmed it would fit in the garage I swapped to 285/75-18 tires that are 3" taller. I used Forscan to set the speedo, I used GPS and got it on the second try. So it is an easy adjustment. Then, why stop at the 126 load tire? The 285/75-18 is a 129 load rated tire.

 

The overall tire diameter of the 275/65R20 is about an inch taller than the 275/70R18 tire option and 2" taller than the 275/65R18 tire option.

The low trim level trucks also have a 17" wheel/tire combo that's shorter still. I believe they are 245/75R17, wrapped around steelies. They make the truck look like it skipped leg day.

 

I did this as soon as the craptastic Contitracs wore out (around 35k) to get the higher load rating. I didn't change anything with FORSCAN, I just add about 2 MPH mentally to my speedo when travelling. Now at 118K with no issues.