Changing front tire size on SRX could void warranty

John Mahler

SPECIAL TO THE STAR

Q: I own a 2005 Cadillac SRX AWD vehicle with P235/65R17 103T on the front and P255/60R17 103S on the rear. The tire company said the size difference is to improve traction and stability. I asked how that works and the short answer was “that’s the way it is”. Can you explain why the two sizes? The owner’s manual just says not to rotate them. Also, if the end result is insignificant, may I replace the tires with same size all around with success?

A: Your rear tires are wider than your front tires by 20 millimetres, but overall the tires are the same diameter and have the same sidewall height. By giving you wider rear tires, the car’s rear traction is improved over using the same size as the front tires.

All cars are designed to understeer when they lose traction. That means they plow ahead instead of turning. If you were to lose control, that is the safest way to lose control. To stop the car from understeering, the correction is get off the gas and gentle braking can help. That is the natural reaction of any driver, when the car is not going where it is aimed. Since GM wants you back to buy another car in a few years, it has ensured you have lots of understeer.

If you switched to one size all round, you would understeer a little less. But before you make that change, you should be aware that GM is fighting any warranty work they can. Should anything go wrong with your shocks, brakes or transmission, the dealer can deny your warranty because you changed the tire size. It would be a total joke; such a small change in tire sizing would not harm anything. But claims have been denied for just this kind of trivial change. So be cautious about a change in size.

Q: Our 2004 Toyota RAV4 is equipped with Bridgestone Dueller H/T P235/60R16 tires, which will need replacement at the end of the season. We have a second set of winter snow tires on rims so winter traction (a weakness of the OE tire) is not an issue. We are looking for a recommendation on a three-season tire that will give a quiet ride with good traction in rain, preferably with raised or outlined white letters. We will be replacing all five tires due to the full-time 4WD mechanism.

A: There are three top tires that I would consider for the RAV4. They are the Goodyear TripleTred, Michelin HydroEdge and the Nokian WR2. All are spectacular rain tires, and are smooth and reasonably quiet. The Michelin has the latest fuel-saving technology in it. The Goodyear and the Nokian are winter snowflake-rated. I know you switch over to winters, but both these tires can stay on the car longer in the fall and switch earlier in the spring.

Q: My daughter has a 2009 Lancer SE with P205/60R16 on alloy wheels. Could she fit P185/65R15 winter tires on steel rims? She has been offered a set free.

A: Sorry, but the tire size is wrong. The diameter of the OE tires on the Lancer is 25.7 inches. The free set of tires is only 24.4 inches. So they are 1.3 inches too small in height. That means the car will look very odd, but more important, it will take more revs to go the same speed, which is bad for wear and tear and it will use more gas.

Q: I was looking to mount 17-inch tires on my Toyota Venza, but there was a notice at the dealer from Toyota that 17-inch rims would not fit as they would touch the brake hardware. Please advise if you know of any 17-inch rims that touch the brakes.

A: No, I don’t know of a 17-inch wheel with a different drop centre that would clear your brake calipers. The vehicle is new to the market, so it will be a while until aftermarket wheel companies start any production. They wait until there are a lot of the vehicles on the road.

Q: I drive a 2000 Chevy Silverado 2500 4x4. I have Michelin all-season tires for summer and Toyo Open Country G-02 for winter. I sometimes tow a fifth-wheel holiday trailer. The sticker on the door says 50 p.s.i. front, 80 rear. My tire dealer recommends 40 p.s.i. all around. What would you recommend?

A: Use the pressures on the sticker. LT tires run at much higher pressures than regular tires because they need to carry a heavier load. This is especially true when you are towing a trailer. At lower pressures, the side walls of the tires flex more and that creates heat and heat causes blowouts. For your truck, 40 p.s.i. is just too low, especially when it’s loaded. I just don’t know what your tire dealer is thinking.

Email tire questions to John Mahler at thetireguy_1@hotmail.com. Please include vehicle's make, model and year, tire brand and size, as well as your name, address and phone number. Due to volume, personal replies cannot be provided.

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