I blew out a tire and need to replace it. I replaced all four tires 2.5 years ago, so I’m assuming I have half life left on the remaining treads (6/32). Subaru recommends replacing all four tires to keep within 2/32 tred depth difference for the all wheel drive transmission. If new tire is 10/32 and old tires are 6/32, do I really need to replace all four due to 4/32 differential?
That or ask the tire dealer if they can shave the new tire to match the other three.
2 Likes
The simple answer is Yes, the tire tread depth must be equalized and the tire must match the other 3. Same make, model, and size. You risk damaging the very expensive all wheel drive if you don’t do this.
4 Likes
They do NOT have to have matching tread depth. They DO have to have circumferences within 1/4" of each other. So theoretically you could put on a tire that has an inherently smaller circumference but that matches the worn circumferences of the old tires. That is not a good idea though, but in theory it would work.
Short answer, buy 4 but keep one or two or the old ones around in case this happens again, assuming you are buying the same make model of tire.
1 Like
not too hard to find a used tire in your size. use CL and search by size
Did you measure it or are you guessing?
3 Likes
I suspect likelihood of AWD damage from slightly different tire circumferences is overstated, but my suspicion and a dollar will only get you a so-so cigar.
have not been to a smoke shop in years. maybe never. can you even buy a $1 cigar?
This is not a quantifiable amount and highly subjective. Would you believe 4/32 difference to categorized as slightly different? FWIW, I wouldn’t. And the warnings about Subarus specifically being susceptible abound. Here’s one example-
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. You may ask what the big deal is? Well, on the Subarus, if all four tires aren’t matched within 1/4" around the circumference, you will break the transmission, not maybe or sometimes - it definitely happens. Granted it won’t happen overnight, and the AWD on many Subarus can be disabled, but the transmissions can definitely get ruined and then they have to be repaired or replaced. Then the cost will be a lot more than the cost of tires!
I agree with the warning that was quoted by Twin Turbo, but this part…
… hasn’t been true for many years. Yes, it can be done with an older Subaru by inserting a fuse into the dedicated fuse holder on the passenger side shock tower, but their newer AWD systems (since… I think… the 2000 model year, or so) do not have that feature.
1 Like
And that theory goes completely out the window when you account for the fact that different tires wear at different rates. So unless you’re sure the new tire will wear at the same rate as the old tires, you’ll still end up with non-equal circumferences.
Not to mention the problem with different levels of grip on opposite sides of the car.
1 Like
Did you intentionally take me out of context or just stop reading at this point and miss the rest of my reply?
Neither. You said it was a bad idea. I expanded on that.
I guess I’ll go to my grave without an explanation of how such a thing happens.
Seems like no one actually understands how modern AWD systems work, except for the guys who designed them.
I don’t know either but it will break your warranty.
this.
Stop guessing and actually find out.