Replacing 1 versus 2 verus 4 tires on M35x - please help

[basilm35x]

I have to replace the front passenger tire on my M35x. All remaining tires have 6/32 of tread life left. The guy at the tire place said that I need to replace all 4 tires because otherwise it will trash the AWD system. If that is the case, am I always at risk of having to replace 4 tires if I have to replace one? Are there any tolerances allowed? Let's say I drive and I have three tires with 8/32 - can I then replace a bad tire and keep the other three? Alternatively, can I replace the front only or rear only?

[Darius]

hahahahaha I love the excuses tire salesmen come up with to sell a set of tires! They are worse than used car salesmen.

Just buy one tire.

[zads27]

Replace 2 or 4 just for symmetry. Is one just flat or something?

[95lstegman]

Replace 2 or 4 just for symmetry. Is one just flat or something?

NO

hahahahaha I love the excuses tire salesmen come up with to sell a set of tires! They are worse than used car salesmen.

Just buy one tire.

YES. tire salesmen SUCK, and they actually know VERY little about the physics and about tires, and even less about cars in general.

[szh]

I have to replace the front passenger tire on my M35x. All remaining tires have 6/32 of tread life left. The guy at the tire place said that I need to replace all 4 tires because otherwise it will trash the AWD system.

At 6/32, the difference to a 10/32 new tire is not that bad that it would mess up even an AWD car. Just buy one tire and then replace all four the next time you need new tires ... maybe you can find another wheel and put the semi-used tire on it for a full-size spare, instead of the dinky ones that usually come with cars today.

If you are still concerned about this, find a place that will shave the new tire (like they do for racing cars) down to the same tread depth. But, this is a waste really.

Z

[Nismo_Freak]

It actually says in the Subaru manual to replace all 4 if you encounter an issue with worn tires.

The variation in RPM is going to be absorbed by the viscous drivetrain. That develops alot of heat, and can erode the differentials life span.

4/32" equates to about 0.75" of slip between the two wheels per revolution. That means your differential is going to do about 1 full rotation of slip per 10 - 12 revolutions of the tire.

That doesn't sound like much until you consider how many times you rotate a tire driving.

What I suggest is putting the low tire on the front. The front is more than likely an open differential, like the GTR, so you won't have the wearing on the rear viscous LSD.