Tire shop claims replacing one tire may damage transfer case?

[o. l. t.]

You would have to have a pretty huge difference to screw up your truck. In the real world this on paper BS goes out the door. Does every tire always have traction and spin at the exact same rate? Does a diff always transfer energy back to the transfer case or does it simply dissipate it by wearing out the other tire in question on the other side of the diff? Unless you are running a HUGELY different tire, you aren't going to do anything except take life from the largest tire between the two on that diff as it scrubs off to try and keep with the smaller tire rotation on the other side. It still works similar to a solid axle when you have limited slip all turning in the same direction. The transfer case will never see the difference as it is handled at the diff FIRST, then if the diff can't handle it the power is handed off down the line. Any small difference is going to be a diff issue.

Having said that, You should find a used tire both for economical reasons of not destroying a new one and to keep the stress off the diff. In my area the tire stores also sell used ones so should be easy to find by calling around to some non corporate stores (mom and pop tire stores locally always carry used tires).

[JCL]

Originally Posted by o. l. t.

You would have to have a pretty huge difference to screw up your truck. In the real world this on paper BS goes out the door. ....... The transfer case will never see the difference as it is handled at the diff FIRST, then if the diff can't handle it the power is handed off down the line. Any small difference is going to be a diff issue.

You are ignoring two issues.

1) While a differential can handle small differences in rotational speed, a constant difference over a long time will wear the diff. Same with the transfer case. The average rotational speed (from the front wheels) compared to the average rotational speed (from the rear wheels) needs to be similar as the transfer case is not designed to handle a constant speed difference over an extended period of time. Failures of the transfer case (more so than the diffs) due to tire differences are a known issue at the dealerships.

2) These vehicles have electronic traction aids. Anythign over a small percentage difference, the computer will intervene. First you will get warning lights, but you can also get individual wheel brakes being applied on the wheel that the computer thinks is spinning (the smaller diameter tire that is rotating faster).

[o. l. t.]

I'm not ignoring it, as stated it would need to be a larger issue than 3mm of tire wear. No tire wears evenly, especially not on these damn SAV's. None of your tires are equal. The idea of wearing a diff over time is ON PAPER only. In the real world the diff accounts for such tiny tolerance. That's it entire purpose in life.

[JCL]

You stated that different size tires wouldn't screw up the truck, and focused primarily on the differential wear issue. Yes, that is what a differential is designed for, and I agree that the wear on the differential is minor.

However, the transfer case wear from constant relative rotational speed difference in the drive shafts is more serious, since there are clutch plates and the heat buildup from the clutches constantly slipping leads to failiure. The tires aren't where the slip happens. The transfer case will see a difference, unless the rear wheels always follow in the same track as the front wheels, even more so if the tires are different front to rear.


And then there is the issue of the electronic traction and braking aids. They don't like different size tires. Lots of exampls of warning lights coming on from that problem, and it is the reason that BMW (and other manufacturers) publish maximum tire diameter differences.

[faz]

Thank you all for your contribution.

I did find a small nearby shop that had a used Michelin which had 5/32 thread left (similar to the other side), so I went and had that installed during lunch hour today. I hated driving without a spare and wanted to get it done ASAP.

The total cost including the tip for the person doing the tire change came to $65.

This should take me a few more months... unless I manage to pickup another nail along the way, in which case I will just replace the whole set.

[TowX]

Fantastic, glad it worked out well for you. Now you can drive with peace of mind for a while.

[Dan Fowler]

Originally Posted by faz

Thank you all for your contribution.

I did find a small nearby shop that had a used Michelin which had 5/32 thread left (similar to the other side), so I went and had that installed during lunch hour today. I hated driving without a spare and wanted to get it done ASAP.

The total cost including the tip for the person doing the tire change came to $65.

This should take me a few more months... unless I manage to pickup another nail along the way, in which case I will just replace the whole set.

The tech guys on here are sooooooo great. Only thing I noticed is the simple stuff. The amount of tread left is not the topic. It's the overall circumference of the tires.

[chuckster]

Originally Posted by Dan Fowler

The tech guys on here are sooooooo great. Only thing I noticed is the simple stuff. The amount of tread left is not the topic. It's the overall circumference of the tires.

Wouldn't the amount of tread left be the determining factor of the overall circumference of the tire? Please correct me if I am wrong. Seems logical to me.

[TowX]

Originally Posted by JCL

You stated that different size tires wouldn't screw up the truck, and focused primarily on the differential wear issue. Yes, that is what a differential is designed for, and I agree that the wear on the differential is minor.

However, the transfer case wear from constant relative rotational speed difference in the drive shafts is more serious, since there are clutch plates and the heat buildup from the clutches constantly slipping leads to failiure. The tires aren't where the slip happens. The transfer case will see a difference, unless the rear wheels always follow in the same track as the front wheels, even more so if the tires are different front to rear.


And then there is the issue of the electronic traction and braking aids. They don't like different size tires. Lots of exampls of warning lights coming on from that problem, and it is the reason that BMW (and other manufacturers) publish maximum tire diameter differences.

Exactly!!

The manufacturers all publish these specs for a reason. BMW (Porsche, VW, MB, GM etc) isn't in the business to sell tires so it's not a profit center rationale. I'ts because they've designed in these parameters for many different reasons. BMW's engineers are the tops in the business, why second guess their specs?

Couple of years ago when towing my trailer back from the east coast I got a nail in the sidewall of one of my front tires in the middle of WV- Monday of Labor Day weekend. Went to put the original full size spare on and found that it went flat moments after I lowered the truck down and put weight on it. Local WalMart was the only thing open that Monday on Labor Day weekend. Naturally they didn't have a 255/50-19 in stock. We inspected the spare- keep in mind this spare was OE and had never been out of the spare tire well other than to check air pressure twice a year- and when we pulled the tire off the rim, the inside of the sidewall was abraded, with lots of tire shavings on the inside. This tire had never been mounted from new, there was still virgin paint on the bolt seat of the steel wheel. But it was junk. And of course they didn't have a 235/65-17 tire in stock. But they had some inexpensive 245/60-17 BFG's.

Calculating the rolling diameter, it should be virtually identical to the 235/65, just 2% or so off. Mounted one up. Hit the road. Within 50 miles I had the ABS light flickering, followed shortly by the Trans Failsafe warning. Pulled off the road, shut down, waited a few minutes, restarted. Drove a while then trans failsafe again. So I found an exit with a couple hotels and quit for the day. Next morning found another tire dealer who had a 235/65 in stock. He even took the 100 mile old BFG in trade! Hit the road and never had a problem again. Went straight to my dealer on the way home and had the codes pulled, was told the rolling diameter difference threw off the ABS and confused the stability control, and that resulted in the Trans Failsafe light. And that was with just a 2% difference in rolling diameter.

BTW- I showed the dealer my spare tire. They replaced it for me without question. No excuses, just good service. And I now carry one of my 255/55-18 mounted snows in the trailer just in case.

[Yii]

JLC you rock..... that video.. it was awesome.