Why is it bad to rotate tyres incorrectly on AWD cars?

Ok i know its bad and I've seen it posted a bunch of places but never with an explanation.

 

Granted, I'm not going to do this (ever) but I'm just looking for a specific technical explanation of what will break.

Any actual stories with results of it happening?

Because if the difference of the tire diameters between the tires exceeds 1/4" it's not good on the center differential. Not rotating the tires properly could cause you to mix tires of unequal wear together on the same axle.

Just follow the recommendations in http://thel7.com/TSB/05-37-07.pdf. Note that the spec.B is equipped with directional tires from the factory.

Ok i know its bad and I've seen it posted a bunch of places but never with an explanation.

 

Granted, I'm not going to do this (ever) but I'm just looking for a specific technical explanation of what will break.

Any actual stories with results of it happening?

 

Like it was mentioned. You want the tires to wear as best and as evenly as they can to try and keep the overall circumference the same or within spec. Otherwise it will cause the transfer clutches to burn out over time.

Ok i know its bad and I've seen it posted a bunch of places but never with an explanation.

 

Granted, I'm not going to do this (ever) but I'm just looking for a specific technical explanation of what will break.

Any actual stories with results of it happening?

 

It helps if you explain what 'rotating tires incorrectly' means? Theres more than one way to improperly rotate unidirectional high performance tires on a AWD car, but ppl may not be thinking the same thing you are and give you the wrong advice.

Yea sorry it was a bit vague. I basically meant rotating the wrong way (the way with the big red 'X' in the manual).

 

blackfang's post about 'burning out transfer clutches' makes sense due to the uneven wear.

 

Thanks.

Devil's Advocate...

 

Our AWD is 50/50, all 4 tires are being worn equally. What difference does it make?

Devil's Advocate...

 

Our AWD is 50/50, all 4 tires are being worn equally. What difference does it make?

If they are not being rotated I can guarantee you they are not being worn equally.

If they are not being rotated I can guarantee you they are not being worn equally.

 

I agree 100%.

 

If you do NOT rotate your tires they will NOT wear evenly symmetrical AWD or not.

But why? Is it because the fronts turn and so wear based on turns? Or maybe because of cornering more on one side wears em more on the outside?

I've heard of rear diffs overeating and causing a fire because one rear tire is turning faster than the other. Most subies have three differentials (front, center, rear) , which can be damaged by mixing in a tire with a tread depth that is 2/32nds and/or a 1/4 inch different in circumferance from the other three. Subaru recommends when rotating tires, move the front ones straight to the rear, and cross the rear ones to the opposite front. For the most even wear, rotate your tires ever 6,000 to 8,000 miles. When switching between winter and summer tires, consider that a rotation. (a good shop will mark the tires and rotate them from where they came from)

Now what about directional tires? They don't rotate properly since you can't turn em.

;2240246']Just follow the recommendations in http://thel7.com/TSB/05-37-07.pdf. Note that the spec.B is equipped with directional tires from the factory.

 

Actually, that is incorrect. The RE050A is "outside directional" which is to say that as long as you don't remove the tire from the wheel, you rotate the tires normally and you're fine.

But why? Is it because the fronts turn and so wear based on turns? Or maybe because of cornering more on one side wears em more on the outside?

alignment, suspension geometry, weight distribution, scrub wear (turning)...

Now what about directional tires? They don't rotate properly since you can't turn em.

 

For directional tires - shift front/rear.

For non-directional tires - rotate as schematic specifies.

alignment, suspension geometry, weight distribution, scrub wear (turning)...

Yep.

 

I have seen tires wear as fast as 15,000 miles. Alignments are key and if you do not have it done yearly or every 15k and don't rotate the tires, they will wear unevenly. Then some make the mistake of changing just the front worn tires.

Devil's Advocate...

 

Our AWD is 50/50, all 4 tires are being worn equally. What difference does it make?

 

I'm sure its already been said, but how can the front tires that do steering and bear the majority of grip load under decel and braking, NOT wear faster than the rear tires that just propel the car, without rotating them?

I'm sure its already been said, but how can the front tires that do steering and bear the majority of grip load under decel and braking, NOT wear faster than the rear tires that just propel the car, without rotating them?

 

Very good point. Thanks

Actually, that is incorrect. The RE050A is "outside directional" which is to say that as long as you don't remove the tire from the wheel, you rotate the tires normally and you're fine.

The Legacy GT spec.B factory tires are definitely directional, so heed what the TSB says about rotating directional tires:

 

http://i41.tinypic.com/11iplwk.gif

For directional tires, you could flip them on the rims to swap to the other side.

;2242836']The Legacy GT spec.B factory tires are definitely directional' date=' so heed what the TSB says about rotating directional tires:[/quote']

 

Brady is correct.

The Potenza 050 tire is directional. The Potenza 050A (which comes on the spec.b and maybe other subies) is not directional. It has an asymmetric (thus, 050A) tread, so there is an inside and an outside, but it can be rotated like a non-directional tire should be.

For directional tires - shift front/rear.

For non-directional tires - rotate as schematic specifies.

I did a search for information on cross-rotation but didn't find what I was looking for so rather than start a new thread figured I'd resurrect this one as it's pretty close to my question.

 

I bought new non-directionals in June and the dealer recommendation was to rotate after the first 4000 miles and then 6k intervals. I passed the 4k point last week so did the rotation this morning. When I checked the owners manual to make sure I would do it right it directed to just switch the fronts and rears, which is what I did.

 

Should I continue this practice on future rotations? Was there some reason (like directional OEM tires) for the recommended rotation and is it better to move the fronts back and then cross the rears to the front as apparently is the new Subaru recommendation? Also is there any significant advantage to using the 6,000 mile interval over Subaru's 7,500 mile recommendation?

 

Also any tricks anybody might have for doing this with a single jack would be appreciated. This morning I borrowed the jack from my Chevy work van so I could have both wheels off on one side but this would become trickier with the cross-rotation.

One way would be to go to a DIY location with a car lift that lifts all four off the ground at the same time.

 

And you can rotate as often as you like, but if you have two sets of wheels (winter and summer) it's a lot easier to perform the rotation since you are changing wheels two times per year.

 

The idea of the rotation pattern is to make sure that the wear is even over all tires, just keep the same pattern every time if you do an all four rotation. Uneven wear can put some strain on the LSD:s, so that's why it's a good idea to rotate now and then.

I'm sure its already been said, but how can the front tires that do steering and bear the majority of grip load under decel and braking, NOT wear faster than the rear tires that just propel the car, without rotating them?

 

Easy. Rear biased center diff, more power than stock, heavy on the gas in tight turns wagging out the back = more wear on the rear than the front.

 

It's not typical, but it could happen. I'm stage 2 and do it occassionally, but you'd have to do it a lot to see more wear on the rear than the front.