does 235/50 18spare do damage used on rear?

[blackout]

I read somewhere in the forum that it will cause damage to something (rearend?) if there are two different sized tires on the rear. That makes sense to me, but wouldn't it make sense to Merc, also? Why would they provide a spare tire that will damage my car? Not sure what to think, except that I need a bigger spare tire. What do other owners do about this? Or is it a 'non-issue' and I really don't need to concern myself with it even if I have to drive 200 miles on the spare.

[RoyLPita]

The clutches in the rear end will wear out faster if the front sized tire is on the back.

[yjmud]

what he said it will wear out the trak-lok clutches

[blackout]

To be sure I understand: If I have the 235/50 18 spare on one rear side, and 245/55 18 on the other rear side, the damage that will be done is to the trak-lok clutches. Will that happen in 5 miles? 50 miles? 500 miles? hard to say?
btw, I am very glad this forum is available and for you that support it.

[RF Overlord]

I thought I heard something like 50 miles is the furthest you should go, but I'm old and my memory is not what it used to be...wait...what was the question?

[yjmud]

on the the older mustang 79-04 with the spare on it would make it do one wheel burnouts in about 5 miles

[EMAS]

Yes it will make the clutches wear quicker but I seriously doubt they will wear out in 5 miles, unless they are already gone. Treat just the way you would a temporary spare and get a matching tire back on there as soon as practical.

[slickster]

I'm having a hard time finding the oem bfg on ebay that where very cheap just cause the outside letters where mounted on the inside

[Bluerauder]

I read somewhere in the forum that it will cause damage to something (rearend?) if there are two different sized tires on the rear. That makes sense to me, but wouldn't it make sense to Merc, also? Why would they provide a spare tire that will damage my car? Not sure what to think, except that I need a bigger spare tire. What do other owners do about this? Or is it a 'non-issue' and I really don't need to concern myself with it even if I have to drive 200 miles on the spare.

The 2003 MM owner's manual says "Your vehicle may be equipped with a temporary spare or a full sized spare". "Replace the temporary spare as soon as possible with a full sized tire."

No mention of a mileage limit; but I have always heard 50 MPH and 50 miles max on the donut spare. If your full size spare is 235/50/18 and goes on the rear, I'd assume that the same 50/50 rules apply and that you should match the 245/55/18 As Soon As Possible. No other info in the manual.

[HiHoSilver]

I guess if you get a flat, put the two fronts in the rear so at least they are the same size.

[blackout]

thank you all. This is most helpful.

[Mr. Man]

OK so I'll complicate this wear on the clutches theory. Say I drive my car for 15K miles and I get a flat on the rear 245 OEM. I replace said tire with a new 245 but the other tire that didn't go flat has plenty of tread to go another 10K. Now the old tire has 15K of wear so it is smaller in circumference than the new 0 mile tire. Are my clutches still in jeopardy or is the difference in circumference within acceptable tolerances?

[EMAS]

OK so I'll complicate this wear on the clutches theory. Say I drive my car for 15K miles and I get a flat on the rear 245 OEM. I replace said tire with a new 245 but the other tire that didn't go flat has plenty of tread to go another 10K. Now the old tire has 15K of wear so it is smaller in circumference than the new 0 mile tire. Are my clutches still in jeopardy or is the difference in circumference within acceptable tolerances?

Yes that will increase the wear on your clutches. How much depends on the exact difference in diameter. On many AWD vehicles they do give a max difference in diameter before you are putting components in danger of excess wear and premature failure. That is one of the reasons that Tire Rack, for example, offers tire shaving, so that the replacement tire will match the diameter of the other 3 on the vehicle. For example Subaru says that tires must be of the same model and their tread depth be within 2/32" of each other.

[Mr. Man]

Yes that will increase the wear on your clutches. How much depends on the exact difference in diameter. On many AWD vehicles they do give a max difference in diameter before you are putting components in danger of excess wear and premature failure. That is one of the reasons that Tire Rack, for example, offers tire shaving, so that the replacement tire will match the diameter of the other 3 on the vehicle. For example Subaru says that tires must be of the same model and their tread depth be within 2/32" of each other.
Oye vey!!:eek:

I can remember a time when all 4 tires were a different brand and more than one was a different size and we loved it. :lol:

[GetMeMyStogie]

People, don't forget the clutches slide against each other every time you turn a corner, take a freeway entrance ramp and cruise along a gentle highway curve. The diff oil with friction modifier is designed for that purpose.
What's the expected life of the clutches under normal conditions? 80k? 100k? More? Yes, driving with slightly mismatched tire sizes on the rear of a limited-slip equipped car will probably cause some extra wear on clutches, but a short trip of a few hundred miles is not going to shave thousands of miles off their normal life. IMHO.

Besides, there will be a particular turn radius that allows the wheels to rotate at the same rate, saving a bit of life ;)

[71cyclone]

Oye vey!!:eek:

I can remember a time when all 4 tires were a different brand and more than one was a different size and we loved it. :lol:
I had to sell my awd Mountaineer [used] because of ,prior owners error on tires ,transfer case was locking up during parking manuvers after a year of service.changed the fluid and traided it on the MM :burnout: