How Using 4 Identically Sized Tires Affects Your Transmission
Nobody wants to hear the news that their vehicle needs extensive transmission repair. Fortunately, you can avoid many transmission problems with proper care. In fact, one of the simplest ways you can help to avoid a catastrophe is just to make sure that all of the tires on your 4-wheel drive (4WD) or all-wheel drive (AWD) vehicle always match.
Modern consumers have begun to drive their vehicles longer, waiting until the cars are an average of 15 years old to sell them. This provides more opportunity to damage a transmission that may cost $8,000 to replace. Although tires may seem expensive, replacing them as needed costs far less than the alternative.
The hubs on some 4WD vehicles are engaged, although not necessarily locked, at all times. On others, you have to manually lock them. Although you may have a little more leeway on manually locking types, your transmission will be ruined quickly on either model if your tires do not match.
Driving on mismatched tires will destroy the planetary gear, which is an integral part of your transmission. This is such a prevalent problem that you will probably have to sign a release form to even get a repair shop to put a single new tire, instead of a whole set, on your 4WD vehicle. Furthermore, you will almost certainly void your warranty by having them do so.
Some people understandably assume that replacing a tire with the same size as the other 3 tires already on the vehicle is sufficient to avoid damage. However, this is completely false. Brands vary in their actual measurements, with an “inch” on one not really equal to an “inch” on another. Furthermore, nearly imperceptible differences in wear degree will result in very perceptible damage to your transmission. You can have a new tire intentionally worn down for a fee, but you might prefer not to pay someone to essentially age your tire on purpose.
Some AWD cars are even more sensitive to tire size than 4WD models. On one popular brand, if the tires vary by more than .25 inches in diameter, your transmission will be destroyed. Again, different tire brands vary widely, and you have a very narrow room for error here. Even variances in tread pattern will be too much for an AWD transmission.
Because of the high price of poor maintenance, you would do well to carefully follow the advice of your owner’s manual. In an effort to save a small amount of money in the short term, you could actually cost yourself thousands in the near future.