Different sized rear tires

[asymptonic]

So in working on the rear end, the shop claims I have a bent rim, which is news to me, and in the mean time they've moved my full size spare, which is a P225/75-r15 onto the passenger rear. The other side is a P235/75-r15. I'll get this sorted out eventually but have a road trip next week. Is this going to be a problem for a couple thousand highway miles? Worried about it's effect on the (new) rear diff.

 

[RCP Phx]

A couple thousand miles is a lot for mis-matched tires. I would go to the charts and look at the revolutions per mile, you definitely need a open diff!

 

[asymptonic]

I do have an open diff, but still don't like it. I'm going to take a look at the rim and possible put the "bent" wheel back on. Alternately may try to get a P235 last minute to mount on the spare to even it out. Thing is I have noticed nothing that would indicate a bent rim, or at least a bad one, and from what I understand, until it's pretty bad the main thing I have to worry about there is losing tire pressure, which is way easier to manage.

 

[asymptonic]

Revolutions per mile I'm looking at roughly 740 vs 722, but not sure what that means.

 

[RCP Phx]

It means your spider cluster is rotating 18 full revolutions per mile, now consider the speed at which you plan to drive. That's really asking for a problem!

 

[asymptonic]

If I'm doing the math right, that's 1260 revolutions per hour, or 1/3rd a revolution per second, at 70mph or one turn every 3 seconds. Seems rather a slow rate of turn. Granted I'd love to have equal size tires, but trying to figure out between slightly mismatched tires and one which may have a bent rim which is the safest to run for a two way 900 mile each way road trip.

 

[RCP Phx]

Then multiply by the side gear to spider gear ratio! Remember the spiders don't have a bearing but run direct on the shaft.

 

[asymptonic]

Again, not an expert here, have run the same diff for 25 years. Is that my main gear ratio? 3.07 x 0.35=1 turn per second? Edit: still trying to figure out whether it's safer to run the 'bent' rim tire or different ratio wheels.

 

[RCP Phx]

Why not put the old tire on the new rim?btw that's not the spider gear ratio.

 

[asymptonic]

NM, I'm dumb. I have a P235/75r15 tire and a non-bent wheel. I just need to get a tire shop to swap the tire onto the non-bent spare wheel and run that.

 

[asymptonic]

Hahah, jinx, we just figured it out at the same time. (edit: and by we I mean me)

 

[lawsoncl]

The front spiders on a disconnect axle also spin all the time, right?

 

[RCP Phx]

The front spiders on a disconnect axle also spin all the time, right?

They can, but they are not under a load!

 

[asymptonic]

FWIW, tire shop found no problems with my wheels but a tire that wouldn't balance. In the end I have a cheap tire on the original rim but with a matching diameter and the old tire on a spare. Not ideal as I don't like running 3/4 same tires but should/hope it'll be good enough for the next 3k mile road trip. Will deal with everything else when I get back.

 

[RCP Phx]

What's the date code on your tires? I never wear a set out but can tell when they are getting old by the way they drive, it's actually do for a full set (5) about now and I always rotate my tires just to keep the tread depth and age the same.

 

[Unclewolverine]

Damn, you guys are picky. I've got 4 different tires, ranging from brand new to almost cords, one of them has a date code at least 10 years old. But I also chew through tires so fast on the mail route it would make your head spin. Soon I'm going to upgrade to 16 inch wheels so I can run 10 ply.

 

[RCP Phx]

Damn, you guys are picky. I've got 4 different tires, ranging from brand new to almost cords, one of them has a date code at least 10 years old. But I also chew through tires so fast on the mail route it would make your head spin. Soon I'm going to upgrade to 16 inch wheels so I can run 10 ply.

OK, but you don't wheel or make any long trips !!!!!!!!!!!!!!!!

 

[Unclewolverine]

132 miles a day, 6 days a week. Plus the occasional camping trip, 4 hours one way.

 

[asymptonic]

FWIW, even with the smaller wheel the diff only measured 150 degrees after about 20 miles at 70mph. Not a super long trip mind but did give me a little piece of mind. I now have matching tire diameters so will attempt the trip.

That said, I still have that bit of vibration between 35 and 45mph under load. Let off the gas it stops, and it's less if it's down hill vs accelerating or uphill. Shop had the rear drive shaft balanced, and all four tires have been balanced. U-Joint? Problem with the newly rebuilt rear diff? It's pretty slight but noticeable. Most easily felt in the steering wheel.

Edit: also did the transfer case shifter adjustment myself with help from the mrs. Didn't do it to the book but it went well and 4wd is working again, so at least that was easy.