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Rob,

Last summer I bought two tires for my Accord. I opted to match the all-season tires that were already on the car.

The guy at the tire shop installed the new tires on the rear of the car. Wouldn't it make more sense to put new tires on the front since my car is front wheel drive?

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Stan from Mississauga

First off; hang on to your tire dealer because he's done the right thing by installing your new tires on the rear axles.

Here's the skinny: tire and auto manufacturers are very concerned about oversteer, a phenomenon that can affect handling and driving dynamics.

Installing only two new tires on a vehicle raises a few questions:

1. What about steering?

2. Shouldn't the tires with the most grip be on the front?

3. Braking is done mostly by the front brakes; shouldn't the grip be on the front?

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4. If my car is front wheel drive, should the drive wheels have the best tires?

Extensive testing has resulted in an industry-wide consensus that new tires must be installed on rear axles, whether the vehicle is front or rear-wheel drive.

After testing every combination of old and new tires under various road conditions, they determined that in each case, the worst combination for handling and driving dynamics was to have worn tires on the rear and new tires on the front axles.

What happened on the skid pad was oversteer. The back end of the vehicle breaks loose during a cornering manoeuvre, and tries to come all the way around to trade places with the front of the vehicle. In essence, the back end of the car is trying to steer the car.

As the name implies, there is an opposite action (Remember high school physics classes?) called "understeer," which happens when the front tires lose traction. The big difference is that understeer is much easier to control and does not affect the vehicle's thrust line like oversteer.

Understeer can be controlled by steering in the direction of the skid or applying the brakes to slow down. Trying to control oversteer using the same techniques can get you in a lot of trouble.

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The worst is braking during oversteer. Applying the brakes will lighten the rear of the car, exacerbating the situation.

So Stan, it's easy to be confused as to why new tires are installed on a rear axle, but now you understand that there are a lot more physics involved that are not obvious to the average driver - more than simply, the four basic questions I laid out earlier.

For those of you that wish to look into this further, please check out:

http://www.betiresmart.ca/pdf/BuyingTires.pdf

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