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Three-pedal evangelist
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Can you even tell just by a visual exam? I wasn't able to find a good source but I recall that any rubber tire over seven years from manufacture could be dangerous.
Yes, dry rot is visible. It starts as tiny "micro" cracks and they get larger over time.

I doubt there is any blanket time that a tire can be considered unsafe. Dry rot can happen in as little as 4 years or may not happen for much, much longer. It can also depend on the composition of the rubber compound. Temperature and humidity swings accelerate it, so tires on a vehicle that is garage kept will last a lot longer before getting dry rot.
 
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2015 XV Crosstrek Premium CVT, 2019 Impreza Sport MT, 2001 Forester S 4EAT, 2013 Outback Premium CVT
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We had a 97 Outback limited auto that came with Michelin MX4 tires (I think it was) the tires just seem to stop wearing at some point. There was a fair amount of tread left but eventually the rubber got so hard the car would lose traction in the wet easily. I guess the only visual exam, aside from dry rot, is to look at the DOT date, depending on where you look 6 years they say but 10 years max? I suppose it depends on where you live and park the car though. Even Discount Tire says there is not exact way to say when they go bad, lots of things to consider I guess >>Link<<
 

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Howdy,

I keep reading about how important it is to replace ALL FOUR TIRES if only two need to be replaced. The reason being that even a slight difference in tread wear will cause you and your loved ones to fly off a mountain and straight into the fiery furnace of hell. [Or something. I might have read it wrong]

Have you ever heard of anyone having problems with their AWD because of tire wear? Have YOU?

Do I have to sweat over this? Or can I rotate them like I normally would with any other car? [I usually have the tires rotated every time I have the oil changed]

Thanks

:unsure:
There are thousands of old (and not so old) Subarus still being driven that do not have their tyres replaced in 4's...and I have never heard of an actual problem
 

Three-pedal evangelist
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We had a 97 Outback limited auto that came with Michelin MX4 tires (I think it was) the tires just seem to stop wearing at some point. There was a fair amount of tread left but eventually the rubber got so hard the car would lose traction in the wet easily. I guess the only visual exam, aside from dry rot, is to look at the DOT date, depending on where you look 6 years they say but 10 years max? I suppose it depends on where you live and park the car though. Even Discount Tire says there is not exact way to say when they go bad, lots of things to consider I guess >>Link<<
I remember the Michelin MX4's well. They were on my 97 Outback when I bought it. Since the car had 61K miles, they were well worn and needed to be replaced. I replaced them with BF Goodrich Long Trail T/A's. Those lasted until I traded the car in at 112K miles. The Long Trail T/A's were great tires. They took whatever conditions you threw at them and were even pretty decent in snow. Unfortunately, my 09 Outback took a different size and I couldn't find Long Trail T/A's in that size when it came time for new tires on that car.
 
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2023 Sport 6 Speed Crystal White Pearl
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Discussion Starter · #45 ·
Was it the transmission that was destroyed or was it the transfer case? I suspect the transfer case.
Here's what the Impreza owner wrote. [In the third paragraph that I left out he was asking for help insofar as how likely it is the tires were to blame. No one answered that question]

"I have a 2013 Subaru Impreza with a continuously variable transmission with ~40k miles on it. About two months ago I blew out the front right tire and took it to a tire shop. The folks at the tire shop said the tire wasn't repairable and that I had to replace two tires. The put the new tires on the back and moved the undamaged, but worn tires on the front. I can't remember if the worn tires were 60% worn or 40% worn, but they were the stock tires that I bought the car with.

About a month ago (and maybe 2k miles after replacing the tires) I started hearing a humming/clicking noise from the car (though no indicator lights went off). I took it to a shop and they told me that the noise was coming from the transmission and that I had to take it to the dealership. The dealer told me that the transmission was shot due to the diameter difference between the worn front tires and the new rear tires. Apparently the front tires are 4/32 thread and the rear are 10/32. The dealer claims that the warranty (which covers the powertrain to 60k miles) is void because the tread difference was responsible for the error. According to the dealer any tire shop should have seen the difference in tread and either changed all 4 tires or shaved the new tires down. The dealership wants ~$10k to replace the transmission"
 

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Thanks for all the messages. I went ahead and bought 4 new tires. Didn't want to risk it. I sort of knew that was the way, but figured I'd check here, too. Appreciate it. The only tire shop within 1.5 hrs of me is really bad, but so far, it's all worked out alright. Thanks again!
 

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Here's what the Impreza owner wrote. [In the third paragraph that I left out he was asking for help insofar as how likely it is the tires were to blame. No one answered that question
Well here is the thing. That person's drive was destroyed bc there were two identical tires on one shaft and two DIFFERENT on the other shaft.

If that person would have put a new one on the front and a new one on the rear there would have been zero problem. WHY? : Your car usually is going straight or close to it. So a new one in the front will run with a new one in the rear or an "old" one in the front will run with an "old" one in the rear. It will be seamless.

Truthfully you can run withy ONE ODD SIZE tire on either the front. There will be zero problems. Thats why you can run 50 miles with the small donut on the rear. The 50 miles is bc of liability issues because of an out of spec tire failing. It has ZERO. To do with drive train failure.

So don't fret about an odd size tire.

Weere It me: I would either have the tire shaved or buy 4 new ones only because sooner or later you will buy 4 newones. So bite the bullet. But its no rush. Disclaimer: my answer is based on engineering commonsense. Don't take my word for it.
 

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This week a friend had a blowout a right rear tire in her Legacy. She initially called me because she remembered me saying something about tires with different sizes being bad and possibly needing 4 tires. Turns out she was waiting for AAA on the side of a very busy highway to come and change the tire. She was there about 2+ hrs. It wasn't that far from me. I got there first and changed it for her. Since the blowout was on the rear no need to swap tires around. She only drove home, maybe 5 miles then to the Subaru dealer where she got the tires originally, another maybe 2 miles. The tires had ~34K miles and were within the road hazard timeframe of 2 years. The dealer said if she wanted only one tire (not something she asked) they would replace for free but she would also sign a waiver in the event of drivetrain damage. She ended up getting 4 new tires but paying for 3.

Info. on the subject from Mr Subaru (skip to 7 min for info on diff sizes)


I'm attaching scans from Subarus end wrench mag they use to send to the dealer service departments from three different issues and a statement from subaru on the subject.

Tire Wear/Rotation/Replacement/Temporary Spare Tire Operation

We all know that tires wear. There are certain things you, as an owner, can do to help minimize this wear.

1. Keep your tires properly inflated. This is perhaps the single most important thing you can do. Information on correct tire inflation pressure is provided in your owner's manual and on a placard on the driver's door pillar. How often you check your tire inflation is up to you. As a rule of thumb, tires should be checked every time you fill your car with gas. Remember that tires should be checked when cold since tire pressure will increase as the tires warm up.
2. Rotate your tires regularly. SUBARU recommends tires be rotated every 7,500 miles. These are recommended intervals only. Your actual driving conditions may warrant more frequent rotation. Factors such as road surfaces, driving techniques/habits, vehicle loading, and weather, to name just a few, can all have an effect on tire wear.
3. When replacing tires, it is always recommended that you choose tires of the same type, size, construction, and manufacturer as those present on the vehicle as original equipment.

On All-Wheel Drive (AWD) vehicles, it is extremely important that the rolling or outer circumferences of the tires be within 1/4 inch of each other. This means that you must physically measure the size of the tire. This is best done with the weight of the vehicle off the tire and at the tread centerline. Also be certain that the tires are properly inflated since this can affect your readings.

If you need to replace just one tire, the same holds true. The measured difference in circumference between the replacement tire and the other tires on the vehicle cannot exceed 1/4 inch.

Depending on the vehicle mileage, it might be better to replace all four tires.

If the vehicle mileage is low and the tires have been rotated and driven at the proper inflation pressures, then you may be within the allowable 1/4-inch difference in circumference.

If the difference between the new/replacement tire and the current tires is within this 1/4-nch maximum, then the tire should be compatible. If it is not, then other tires will need to be replaced to conform to the 1/4-inch rule.

Exceeding this 1/4-inch difference in tire circumference can place unnecessary wear on drivetrain components, possibly causing them to wear out prematurely.

If your vehicle is AWD (All-Wheel Drive) with an automatic transmission and the temporary spare tire has been installed, put a spare fuse (15 amp) inside the FWD (Front-Wheel Drive) fuse holder (refer to your owner's manual for location). Confirm that the Front-Wheel Drive (FWD) warning light comes on before you drive the car. Installation of this fuse deactivates AWD to prevent possible damage to the drivetrain components that can result due to the use of the smaller temporary spare tire. After re-installing the conventional tire, remove the fuse from the FWD fuse holder to restore AWD operation.

For more information on tires and temporary spare tire usage, always consult your Subaru owner's manual.





Font Screenshot Number Document Parallel


Font Document Symmetry Number


Tire Wheel Automotive tire Tread Motor vehicle
 

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I appreciate all the arm chair engineering and what seems to be solid math involved. For me though, if I am on used tires and have 1 bad one, I will replace all 4. It is just not for me worth the risk of long term damage/wear on the driveline. Over cautious, waste of money or whatever it is, that is just the cost of owning an awd in my mind. Having had my cherokee now for many years, tires were always in pairs at minimum anyways but better with a full set. I see it as a good chance to get fresh rubber under me, the single most important part of the vehicle, contact to the ground can never be to New for me and no downside to 4 brand new tires. Plus, you can always find someone willing to buy your used tires to help offset the cost of new tires if needed. I just wish we had a Full Size spare 馃く.
Topics like this can never be settled but I appreciate they exist to help people make their own choices.
 

Three-pedal evangelist
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I appreciate all the arm chair engineering and what seems to be solid math involved. For me though, if I am on used tires and have 1 bad one, I will replace all 4. It is just not for me worth the risk of long term damage/wear on the driveline. Over cautious, waste of money or whatever it is, that is just the cost of owning an awd in my mind. Having had my cherokee now for many years, tires were always in pairs at minimum anyways but better with a full set. I see it as a good chance to get fresh rubber under me, the single most important part of the vehicle, contact to the ground can never be to New for me and no downside to 4 brand new tires.
Or you can buy tires in sets of 5 and use the spare in the rotation. Then if one tire becomes unusable, you still have 4.

What I would like to know is at what point of wear should a new tire not be added to the used 3? Most new tires have a tread depth of 10/32" to 12/32". The law states that 2/32" or less needs to be replaced. Common sense says 4/32" is as shallow as you should go. For snow tires, that minimum recommended tread depth is 6/32".

Plus, you can always find someone willing to buy your used tires to help offset the cost of new tires if needed.
But who would want to buy a set of 3 used tires?
 

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According to the video above from Mr. Subaru @ just before 8 min in he says all tires need to be within 2 - 3 - / 32nds of each other front to back side to side.

I agree the least I'd like to drive around it is 4/32nds on regular street tires.
 

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Subaru once told me that if the tires have 15k miles or less you can get away with replacing one or however many need to be replaced nd not have to buy all 4. Anything more than 15k miles you have to replace all 4. FWIW
 

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Dry, wet pavement, hot weather, and bias-freezing temps the diameter differentiation .. never mind.

You hit your go or stop pedal you're seeing the rearview mirror or flashing lights dead stopped. Stopping is the G-Force vs traffic and condition grip.
 

Three-pedal evangelist
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According to the video above from Mr. Subaru @ just before 8 min in he says all tires need to be within 2 - 3 - / 32nds of each other front to back side to side.

I agree the least I'd like to drive around it is 4/32nds on regular street tires.
I just found this from Tirerack. They say Subaru's recommendation is no more than 2/32" difference:

Manufacturers Recommendations
AudiAs published in their vehicle owner's manual, "rolling radius of all four tires must remain the same" or within 4/32-inch of each other in remaining tread depth.
PorscheCayenne within 30% of the other tire on the same axle's remaining treadwear.
SubaruWithin 1/4-inch of tire circumference or about 2/32-inch of each other in remaining tread depth.

 
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Curious to see how much it would $cost$ to repair what ever damage would accrue, (Worse case scenario) by not following the guidelines of the manufacturer, and compare that to the $cost$ of 4 new tires.

Is it worth the risk?
If costs are comparable, I'm sure replacing tires is an easier process than component repair.

Doug
 

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2021 Crosstrek Outdoor - "Trekov"
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To the OP ... yes, differing tread depths or tire circumferences on Subaru`s symmetrical AWD system will create driveline bind and be a problem. Also factor-in the possibility of needing to use your under-sized, space-saver, doughnut spare tire. Subaru`s own imperatives regarding where to position the undersized spare tire, regardless of which tire is punctured, is very telling.

The justification for (and granted, the logistical headache of) carrying a full-size, matching spare tire and incorporating it in a rearward cross 5-tire rotation pattern at every oil change just keeps getting better and better ...
 

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I always thought the spare (donut) tire placement was to not have a tiny donut in front for steering and braking purposes. It is better suited for just rolling in the back鈥 Could be related to the awd also but I would never choose to use a donut on the front with any vehicle.
 
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