Got a puncture today in my two month new Michelin LTX, MS2 tires today. I'm useually pretty savy with automotive mechanics, but going to play stupid here as I dont really know the answer.

So I have a 2011 F-150 Scab, "2wd" 5.0L which came with Fords optional Limited Slip Differential. I believe I also have the "mechanical" LSD which uses clutch plates as opposed to the '12+ E-LSD type that Ford switched to.

My question is this... I changed out the sorry excuse for OEM tires that came on this truck, and made it look like it was riding on roller skate tires P265/60R 18" Michelin LTX A/S for OEM FX4 sized P275/65R 18" tires.

This thankfully raised my truck 1" and filled out the wheel wells nicely and now makes the truck look like a real truck. The bad news is that my spare is the same size as what came on the truck from the factory. My flat tire is also a rear tire.

Seeing that I have a mechanical LSD rear-end, will I prematurely burn-out or wear- out the unit if I put the 265/60 spare on the rear? Or should I just do what I already think is the correct answer and pull a correct size off the front and move it rear?

Any help greatly appreciated in advance.

 

Well if the outer diameter of the tire is the same then it would be ok. If it is not...I would not put that tire on the rear as it may cause problems with the LSD with a different size tire on the drive wheel. It may try to lock up the LSD as a result IMO.

You can put the original spare on the front and then take the good newer tire and put it on the drive wheel. Do you self a favor and get the same size tire on the spare.

 

Great, thanks. I figured that probably wasn't a good idea. I went ahead and put the spare up front and moved a matching tire from there, to the back.

I was just curious now, If I had to put that spare on the back, would I have killed my LSD?

Yeah your definately right about needing a matching spare.

 

If you drove with it like that for a long time it would tend to tear up that smaller diameter tire. I don't think it would necessarily ruin the rear end but it is possible. Since you ran those Michelins for awhile it is possible you may be worn down close to the outer diameter of the spare...in which case it wouldn't matter too much. If you had an open differential it wouldn't matter so long as you are not engaging 4 wheel drive.

That is the one thing people never think about when changing tires (myself included...ha) until you are faced with having to use the spare. I would imagine a tire shop might take your new spare pro rated for the newer Michelin and you pay the difference...it's worth a try.

 

Didnt think about that, since the spare is a new OEM Michelin that has never been used. Will see if they go for that, got tires from Americas tire.

 

The LSD has clutch packs and different circumference tires will cause premature wear on those packs. Best, CB

 

Thanks guys for all the helpful insight on this. I either need to buy a matching spare now or always carry two jacks lol.

 

I bought a matching spare in my case. Unfortunately I had 20" rims and my OEM spare was an 18" spare. So I ended up buying 1 new tire and 1 new rim with similar to OEM back spacing (and as cheap as possible). So now I at least have matching tire sizes in all 5 spots. And just an FYI for anybody, yes you can fit a 35 x 12.5 R 20 up under there, you'll just need to bend the exhaust shield away from the tire so you don't slowly melt the rubber back there. But that's as big of a spare as you can fit.

 

only need one jack.

change front tire first, set'er down, then change the rear

FWIW, i had a flat on my old work truck (99 f150) on the rear about 20 miles from home. that truck was upsized to 245/75/16's and the original 235/70/16 spare. had to drive it the 20 miles home and another 5 or so to the tire shop and no harm was done to the LSD. I did keep my speed down to 55mph with the spare on. but the LSD worked like a charm until the day it went to auction.

is it a concern? yes.

but in most real world situations, no harm will be done if you limit the time spent on the spare.

just my experience.

 

good choice on not putting that spare tire on the rear. I work at Americas Tire and heard a story similar to yours but a customer wanted the spare tire on the rear and well... couple thousand dollars later (out of our company pocket) found out we were right and the customer was wrong. Manager told him that would happen but he didn't listen. Your differential can take a beating from doing that. Just a little tip, what some customers do (if the spare rim is the same size) when they purchase 4 tires, take your best tire out of the old 4 on your vehicle and make it your new spare so your not sitting on an old spare tire or off set size