I own a Subaru and a 2005 Silverado. I am told that when a tire blows on a subaru you need to replace all 4 tires–otherwise the new tire (which is slightly larger) will cause transmission damage. I am told the same is true on 4x4 which don’t have manually locking hubs.
Who told you this? You can cause problems with mismatched sizes, but worn tires are stretching the concept a bit.
I don’t know about the Silverado but the Subaru can be damaged by using mis-matched tyres
I think that the Subaru is among the vehicles that need well-matched tires. You might consider buying an extra wheel and tire and rotating them in. You can have a replacement tire shaved to match the other ones.
I had the manager at a national tire dealership tell me about the impact on transmission when replacing just one tire.
From the discussions I’ve read on this board, that is correct, but as Beads(and beads 
said, you can have a replacement tire shaved to match the other 3 instead of buying 4 new ones. If that tire dealership won’t do it, go someplace else that will.
It is required to keep all the tires the same due to Subaru’s AWD system.
Those cars that are sensitive to this have warning to that effect in their owner’s manuals.
Did the nice, smiling salesman tell you about this design defect in this vehicle before you bought the car? This requirement for replacing all tires or a new one shaved to match the others when one fails regarding a Subaru and some other brands seems to be blindly accepted by many but I would regard is more as consumer fraud to not alert a customer of this unusual requirement. Historically, cars have not been sensitive to one new tire added to three partially worn. I may never know how this got past consumer’s scam sensors.
I’ve learned one thing here, I don’t plan to ever buy a Subaru if it can’t handle having 1 new tire and 3 used tires on it. A 4wd that is that fragile ain’t worth the driveway space to park it.
I understand the theory here. In a 4WD most anything to disengage the 4wd and put it back in 2wd one of the tires on the disengaged axle has to be able to spin while the other sits. For instance if I take my Dodge into a muddy job site and have to drive in say 1000’ into mud, turn around and leave, when I get to the hard road, if I forget to disengage the 4wd before I get to the blacktop, I may have trouble getting the hubs unlocked unless I drive into gravel somewhere so one of the wheels can slip. I have had to jack one wheel up and hand spin it to get it to unlock, but I don’t see that being related to one tire being half an inch taller than another.
Skipper
If it’s an “all wheel drive” vehicle that powers all four wheels, you typically should replace all four at once since there will be increased strain on the device that equalizes the number of revolutions between the back wheels and front wheels. A “four wheel drive” vehicle does not have this device, since it only powers all four wheels when you are in slippery conditions and transmits revolutions front to back at a fixed ratio and relys on the wheels slipping and sliding to allow you to turn.
It can be difficult figuring out exactly what system you have though, because the terms are often used interchangably. Your Subaru definitely has AWD, as all of them have for decades. The Silverado is probably a 4wd, but I believe it is avaliable with a “full time 4wd” system which is the same as AWD. If you have to push a button or move a lever to get it into 4wd, it’s definitely a 4wd, though there are also automatic 4wd’s that don’t have any controls in the cabin.
Oh, and the hubs don’t mean anything since there are plenty of vehicles with 4wd that have either automatic hubs or no disconnecting hubs at all.
Subaru= yes depends on tread depth
Siverado=NO
maico