Where position to Install Paired Tires?

It's a common problem: On front-wheel drive cars, the front tires get a lot more wear than the rears. Between power transmission and steering, usually front tires get about double the wear, so that if the tires are not rotated consistently, when they wear out the rear tires are still only half worn. It would be expensive and wasteful to replace all four tires, but it's usually good enough to replace just two tires on the same axle, so that the tread depth is the same across the axle.

But this brings up the question – which axle should the new tires go on, front or rear? There are actually very few questions in the tire world on which you can hear so many wildly diverging opinions for a question which has only two possible answers. Ask ten tire people, and you'd probably get an even split between “front” and “rear”, but ten different opinions as to why. Common sense would hold that since the front tires handle the steering and power, the newest tires should be on the front. But common sense in this case is not only wrong but genuinely dangerous. Here's the facts.

The danger in putting the worn tires on the rear axle is hydroplaning. Tires have deep grooves and channels designed to evacuate standing water out from under the tread as fast as possible. When the grooves of the tire fill with water faster than they can evacuate it, the incompressible nature of water can cause the tire to lose contact with the road, resulting in a loss of control. Worn tires are much more susceptible to hydroplaning because the grooves are shorter and can contain and evacuate less water.

The rear tires of a front-wheel drive vehicle are also somewhat more susceptible to hydroplaning, both because they are on the lighter end of the car and because they are being driven by the front wheels rather than applying power to the road themselves. Add in worn tires to this mix, and you've created a situation where the rear tires are very likely to hydroplane in standing water, while the front tires are much more likely to maintain their grip.

When that happens you get oversteer, where the front end will turn but the back end breaks loose and kicks out – as opposed to understeer, where the front end will not turn, but continues on it's original vector. If the rear tires hydroplane while the front tires do not, the result is nearly always an extremely dangerous oversteer condition that can easily lead into a full spin. That's scary enough on a test track, but all too often fatal on a rainy highway.

To avoid this, always put the two new tires on the rear axle to even out the grip differential from front to back. To pre-emptively avoid the problem, however, it's best to always rotate your tires as the manufacturer recommends. This will equalize the wear on your tires before the differential in grip becomes too large.

source: http://tires.about.com