I was told by a discount tire store that when I needed to replace one tire that I should replace all four. They said that not doing so might damage the differential or transmission. Is this correct?
Don’t know what AWS means. But if you are referring to a All Wheel Drive vehicle than the answer is yes it very well could cause expensive damage. More than a set of tires I would venture.
Some tire places will SHAVE the new tire down so it matches the other three older tires.
A lot depends on how many miles you have on your tires now. If there isn’t much mileage, then you might be OK replacing one. If there is even moderate mileage, you should replace all four. The issue is tires of different diameter driving the vehicle. If this goes on for more than a short while, your differential and maybe your transmission will be damaged. Short while means using the donut spare to get to a place where the original tire can be fixed. How many miles on the tires, and how much tread is left on the remaining three tires?
How many miles and tread depth left and age of the tires? could be a prudent decision but more info needed.
Some AWD systems are apparently extremely sensitive to mismatched tire diameters. I know some Subarus have provisions to disable the system (by inserting a fuse) when using a temporary spare.
Some vehicle manufacturers recommend that all tires maintain the same
rolling radius and circumference, while others suggest that all tire
circumferences remain within 1/4- to 1/2-inch of each other. Other
vehicle manufacturers recommend that all four tires remain within
2/32-, 3/32- or 4/32-inch of each other, or within 30% of each other
in relative remaining tread depth.
Here are recommendations from some of the manufactures that Tire Rack
currently serves for matching the tires used on their four-wheel drive
and all-wheel drive vehicles. Additional recommendations from other
Original Equipment Vehicle Manufacturers is pending.
Audi As published in their vehicle owner’s manual, “rolling radius
of all 4 tires must remain the same” or within 4/32-inch of each other
in remaining tread depth.
Porsche Cayenne within 30% of the other tire on the same axle’s
Subaru Within 1/4-inch of tire circumference or about 2/32-inch of
each other in remaining tread depth.
The subaru manual is vague about tires, only stating the following:
When you replacing or installing tire(s), all four tires must be the
same for following items.
© Speed symbol
(d) Load index
(g) Brand (tread pattern)
(h) Degrees of wear
But obviously they are never identical. Even 4 new tires from the
manufacturer are not identical in circumference. There has to be some
tolerance. But Subaru is silent on this.
“I know some Subarus have provisions to disable the system (by inserting a fuse) when using a temporary spare.”
That was the case with older Subarus, but IIRC, that provision hasn’t existed on Subarus since somewhere around–perhaps–2003. In any event, the OP has a Hyundai of some sort, and I don’t think that Hyundai has ever used that approach.
If the OP would divulge the total number of odometer miles that his/her tires have been on the car, and/or the actual tread depth of the tires, we could be more specific with our advice.