First I want to say I'm new to the SHO forum. Ive been a Powerstroke Excursion owner and still am. But I just purchased a 2016 Black SHO with PP and only 2300 miles on it for my wife. I just picked it up and I see it has 2 different size tires (245/45/20 on TSW Nuburging rim on front) and (275/40/20 on back). Im new to the AWD but know this my cause a issue in driveline . The car has lowering spings on it also. My question is, do you think I should replace the rear setup to match front or will this work. Thanks you, Citysmoke
Miss Matched tire sizes
- Thread starter citysmoke
- Start date
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luigisho
SHO Member
If it were my car I would get matching tires. I don't spend alot of time on the new SHO platform as I own the older stuff. However, it has been my impression over the years that AWD and 4WD vehicles should have the same circumference tires or risk damage to the differential or whatever ford awd cars name that piece.
SM105K
Streetlight Grand Prix Champ/ IG @fafomotorsports
I concur
You will need to replace all 4 tires. Most tire shops won't sell/install just 1 or 2 tires on an AWD vehicle. Since all the tires need to match, 2 new tires won't match 2 used tires.
If you find a good shop, they might offer you a trade in on the tires that you have. We ran into this leaving the St Cloud convention in 2012. One of the guys hit a *** hole and had to buy 4 new tires but the shop gave him a credit towards the 3 good ones.
If you find a good shop, they might offer you a trade in on the tires that you have. We ran into this leaving the St Cloud convention in 2012. One of the guys hit a *** hole and had to buy 4 new tires but the shop gave him a credit towards the 3 good ones.
luigisho
SHO Member
Yes. Circumference also includes tread depth differences and, not surprisingly, no one wants to be on the hook for that.
With AWD it's the circumference not tread width that matters. 245/45 and 275/40 are the same(or close enough to the same) diameter that is not an issue. There are a few guys including bpd that are running staggered setups.
Thank you for the quick responses. I think for a piece of mind i will bite bullet and replace rear rim and tires. the front only have 2300 on them. and by the looks of the rear rim angle ,not sure if they did the proper alignment with camber bolts. I will get a alignment done. Thanks
krewat
SHO Member
With the pulse-width-modulated clutch pack that we have driving the rear wheels, it's not THAT much of an issue with slightly dissimilar tires. I will say, though, my observations have been that this thing drives like a locked-up 4WD pickup truck transfer case when I really get on it. (That's on a PP-equipped vehicle, but that might not make a difference really)
luigisho
SHO Member
Lostneye above is correct. I just spoke in general terms but the math on the tire sizes is within 1/10". The same revolutions per mile on both sizes. I have seen recommendations not to go anywhere from 1/2"-1/4" circumference out. The sizes you have are within spec mathematically.
https://tiresize.com/tiresizes/275-40R20.htm
https://tiresize.com/tiresizes/245-45R20.htm
https://tiresize.com/tiresizes/275-40R20.htm
https://tiresize.com/tiresizes/245-45R20.htm
krewat
SHO Member
If I don't rotate my tires, the fronts wear way faster than the rear. But I'm merciless. 
They are the same diameter meaning as luigisho said the same revolutions per mile. Aside from not being able to rotate them front to back there is no issue.
Edit: I read your post as rotations per mile not rotating to keep even wear. Either way I don't see the point of spending money on new tires now to avoid spending money on new tires later.
If the camber is off a different set of tires won't change that. Either have it aligned, adding the correct camber bolts if necessary or swap stick springs back in and have it aligned.
limited02
SHO Member
Double check the wheels aren't staggered as well before you buy same size tires or rotate because that is a common tire size for 20x8.5 and 20x10 wheel setups.
As long as you buy the tires in pairs on an axle, you should be fine. Both tires for the front, or both tires for the rear. No need to buy all 4 even if all 4 are the same size. Just resist the temptation to wear them down to legal depth limits (2/32). Ford's i-AWD 0r intelligent AWD system makes it all happen 4 you.
Johnbigdog
SHO Member
There is a tire size calculator on tiresize.com.
I used this heavily to help others as well as determining the most cost effective tire when minus sizing (is that the corect term for the opposite of plus sizing?) my wheels for the police interceptor rims (18 inch). It worked great considering i never thought about the distance between the tire and strut.
I used this heavily to help others as well as determining the most cost effective tire when minus sizing (is that the corect term for the opposite of plus sizing?) my wheels for the police interceptor rims (18 inch). It worked great considering i never thought about the distance between the tire and strut.
SM105K
Streetlight Grand Prix Champ/ IG @fafomotorsports
Looks good, I like it.
luigisho
SHO Member
It would be the same as all the same size and either end wearing faster than the other. The downside is you can't rotate all 4 to prolong use-able tread life. I would not worry about that very much. The bottom line, since everything is dimesionally legit, is personal preference unless the alignment is way off. I like the way it looks but I don't have to live with it so really you get to choose. I'm not sure if you will get any push back at a tire install place or not. If you do, you can always pull 2 wheels off the car, get new tires installed, and put them back on yourself.
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