Do I really need 4 new tires?


I have a 2005 Subaru Forrester. We replaced the 4 tires July 2006. We’ve put 17,0000 miles on the car since then and yesterday we discovered one rear tire had been slashed and the tire needs to be replaced. The dealer (where we got the tires last year) says we must get all new tires or risk damaging the all wheel drive system. Is this true even when the tires aren’t that old??



if the tires are different sizes they will wear the full time differential down. the differential depends on all the tire circumference being the same.


Yes, you absolutely need four new tires. The Subaru AWD system needs to have four tires that match as closely as possible. The damage to the AWD system that can result from mis-matched tires is more expensive to repair than the cost of the tires.


Your tires may not be “old,” but they’ve accumulated 17K miles. Buy four.


Likely yes. The allowed difference between tires is 1/4" of average circumference of three other tires.

However an alternative is to call and to order the OEM tire. You give them the current average of measured circumference of the three other tires and tirerack can shave it down and deliver it to you or dealer.


That’s one of the drawbacks of a AWD system.


That’s what they say. Four new tires. Frankly, I’m skeptical, but not certain enough to advise someone else to ignore the cautionary warnings. Better replace all four.


Thank you all for confirmation of the bad news. Guess I’ll have to keep the car in the garage!!


Four new tires. Frankly, I’m skeptical

That’s the way the AWD systems are designed. If one tire is rotating faster then the others it will cause SERIOUS damage to the AWD system. It should be spelled out in the owners manual.


“It should be spelled out in the owners manual.”

Yes, exactly! That’s why we ALL should be skeptical. Aren’t we all forever preaching that the owner’s manual is THE bible of your car? But, as I said, I cannot advise anyone to go against the popular notions.


Interestingly enough not all AWD systems suffer from this. Subaru seems to be the more picky followed by Audi however its a true AWD system always engaged. I believe the after the fact type AWD’s don’t have such a strict requirement however the AWD is not as good as Subaru/Audi in severe conditions.


Keep your other three just incase you ever need one tire again.

If you have not been rotating the tires regularly, then you may have a difference between the front and the rear. If that is the case, you may be able to get by with only two tires.

You should get a tire depth gauge, they only cost a couple of bucks. New tires typically have about 11/32" tread depth new. Your car can tolerate a difference of about 2/32" from the best to worse. Usually the front wear the fastest. If a front tire was slashed and the two rear tires are 9/32" or deeper, then you only need to buy two tires and save the one good one for any future needs.

If it is a rear tire that was slashed, or you don’t have two tires that are 9/32" or deeper, then you have to get all four, but again, save the good ones for future use.