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Discussion Starter · #1 ·
In need of some help. I just went of out town from where I live to pick up a 2015 Subaru Impreza. Didn't notice until after I drove on the highway 3 hours to get home, but the drivers rear is a different cheap brand tire which is brand new with 9/32 tread and the other 3 tires on the car are at about 5/32 tread. All four tires are still 205/50R17

My question, getting over that the out of town dealer is horrible. Do I need to put on 4 new tires being that the car is AWD? and did I hurt the rear differential on the highway drive you think?

Thanks!
 

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I don't think a one shot trip would totally smoke it but I would venture it has been there for a while. I would contact the dealer tomorrow with the concerns. Your options are a new set of 4 or one matching tire trimmed to match the rest

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Isn't it recommended with AWD vehicles to change all 4 tires at the same time? In other words, if you have a failure of one tire, it is recommended that you change all 4.

https://www.angieslist.com/articles/do-i-need-replace-all-four-tires-same-time.htm

Subarus: Subarus have, to our knowledge, the tightest tolerance of any AWD system. Since we see so many, we can tell you what the tolerance is. It can be stated in two ways: The first is 2/32nds tread depth across all four tires. The problem with this is that actual tire dimensions can vary from brand to brand and even from model to model. Therefore the 2/32nds rule is only good if you have the exact same size, brand, and model tire. The other way to check is to measure the tire around the circumference and then the tolerance is 1/4". That was circumference, not diameter, so you have to have a flexible tape ruler and measure around the tread of the tire. Also, having air in the tire affects the circumference. Though the change due to having air in it is only about 1/8", it's pretty critical since the tolerance is only 1/4". Therefore, to get an accurate measurement, it's necessary to let the air out before you measure (since the prospective replacement probably won't be aired up). This second method allows you to check compatibility with any make or model of tire. When we were almost finished with this article, a Subaru came in that needed only one tire, so the picture shows us measuring the prospective replacement tire with our "Subaru Tool".

Tires 101 on Tire Matching on All Wheel and Four Wheel Drive :: Souza's Tire Service
 

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Isn't it recommended with AWD vehicles to change all 4 tires at the same time? In other words, if you have a failure of one tire, it is recommended that you change all 4.

https://www.angieslist.com/articles/do-i-need-replace-all-four-tires-same-time.htm

Subarus: Subarus have, to our knowledge, the tightest tolerance of any AWD system. Since we see so many, we can tell you what the tolerance is. It can be stated in two ways: The first is 2/32nds tread depth across all four tires. The problem with this is that actual tire dimensions can vary from brand to brand and even from model to model. Therefore the 2/32nds rule is only good if you have the exact same size, brand, and model tire. The other way to check is to measure the tire around the circumference and then the tolerance is 1/4". That was circumference, not diameter, so you have to have a flexible tape ruler and measure around the tread of the tire. Also, having air in the tire affects the circumference. Though the change due to having air in it is only about 1/8", it's pretty critical since the tolerance is only 1/4". Therefore, to get an accurate measurement, it's necessary to let the air out before you measure (since the prospective replacement probably won't be aired up). This second method allows you to check compatibility with any make or model of tire. When we were almost finished with this article, a Subaru came in that needed only one tire, so the picture shows us measuring the prospective replacement tire with our "Subaru Tool".

Tires 101 on Tire Matching on All Wheel and Four Wheel Drive :: Souza's Tire Service
That would be insanely expensive. You can easily shave a tire down to match the other tires. Just make sure all 4 are the same brand/style.
 

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That would be insanely expensive. You can easily shave a tire down to match the other tires. Just make sure all 4 are the same brand/style.
It is expensive, but it's something you should be educated about when buying a Subaru. Also, hardly any tire places will shave a tire for you. Tire Rack will, but I wouldn't trust that. I'd just buy 4 new tires.
 

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Discussion Starter · #6 ·
Thanks for all the info guys, this is my first AWD car so I didn't know the general rules for everything. It's just about winter time here so I'm just going to buy my winter rims and tires next week and throw them on. I'll worry about buying new summer tires next spring. I hope a little city driving for a week doesn't do too much harm!
 

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It is expensive, but it's something you should be educated about when buying a Subaru. Also, hardly any tire places will shave a tire for you. Tire Rack will, but I wouldn't trust that. I'd just buy 4 new tires.
The other part of this is that although you may be putting the same size tire from Brand P as the other 3 from Brand D, they may be different sized. Simply put a 275x35x20" Goodyear has a different outside diameter than a 275x35x20" from Continental.
 
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