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According to the Owner’s Manual Saab 9-3 M2001 (front-wheel driven cars):

WARNING When fitting just one new pair of tires, these should be fitted to the rear wheels, as these are more critical to the directional stability of the car (e.g. on braking or in a skid). The existing rear tires should therefore be moved to the front. Always move left rear to left front and right rear to right front, so that the direction of rotation remains the same.

This is somewhat counterintuitive to me. Is it indeed recommended (by other sources) to have the least-worn tires at the rear wheels?

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Perhaps I should add that I find this warning somewhat counterintuitive particularly if the worn tires that stay on the car are still in relatively good shape. (So, when they are certainly not excessively worn.) –  Glen The Udderboat Aug 21 '13 at 16:55
    
Also worth noting: If you're going to swap out just one tire, you should probably put the new one on a non-powered wheel. Otherwise, this might happen. –  Iszi Aug 21 '13 at 21:38

2 Answers 2

From what I have seen and read over the last few years the "general rule" has become best tires on the rear. In my opinion it is likely the result of litigation by people who were involved in skidding accidents. The theory as far as I understand it, is that with worn tires in the rear, the back end can loose traction and allow the rear of the car to attempt to pass the front while in a high speed turn or emergency braking situation. Any resulting inability of the driver to steer into the skid would become an inherent design defect when the case comes to court. I assume it has been determined by lawyers that it is safer to get stuck in snow because the best tires are on the back, than risk an incident of the back end coming around because you were going to fast in the first place.

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Yes - putting the best tires on the rear will preserve the understeering bias that most "car as appliance" drivers will expect. –  Bob Cross Aug 21 '13 at 12:31
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+1 for the answer and @BobCross, both well-informed. I would add that I feel the best approach here is to avoid this traction imbalance problem altogether by routinely rotating tires such that there isn't a large discrepancy in wear between front and rear. The statement from the owners manual should not be taken as a recommendation against regular tire rotation. –  mac Aug 21 '13 at 14:59
    
@mac But they certainly seem conflicting recommendations in case of front-wheel drive. For front-wheel driven cars the front-wheels will wear more than the rear wheels. Reducing any discrepancy between front and rear would require to fit the new tires on the front wheels, so that, after time, they will become just as worn as the back tires. I think there is a conflict here. You seem to narrow the manual's recommendation as applying only to situations where you have two new tires and two excessively worn tires. –  Glen The Udderboat Aug 21 '13 at 16:43
    
@mac, yes, following the recommended rotation procedure is important and is specific to the configuration of the vehicle. For example, my AWD car permits rotation front and back but not side to side (so my left tires will always stay on the left). Rotation will mitigate many uneven wear situations but not prevent them. –  Bob Cross Aug 21 '13 at 17:00

It really depends on the car... and I mean on which wheels is the traction.

Usually front wheel traction cars should have the better tires on the front wheels. But that doesn't mean that having good on front and highly used on the back makes it safe. The problem is that with usage, the technical caracteristics of the tire change and if a tire is tested to stop in 60 meters (for example) from 40-0 mph, a worn down tire will do it in 70 meters. This will cause an imbalance between the front or the rear. Fortunately many modern cars have ABS and the ABS sensor improves stability and safety even though there is a difference in the tires. From experience I do not recommend changing tires 2 by 2 because this will wear down the new tires faster than usual.

If your example is the Saab 9-3 (I had a convertible one :) ) then I recommend to have the least worn tires on the front because it's a front wheel traction car. If your car is a BMW, then having good tires on the back is more crucial. (Especially in winter time) Also it is very important to have winter tires in the winter, as the physical characteristics of the tire are different ("summer" rubber is made to be sticky, but at low temperatures it becomes hard, so if you have worned out summer tires on the front wheels and driving on the highway in a cold winter day, it is highly possible that you will turn the steering wheel and nothing will happen).

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The line of thinking you describe implies that drive traction is the most important characteristic. Drive traction is not generally a life-safety concern, while stability in cornering and braking certainly are. The logic behind the quote from the owners manual that the OP provides applies to both front- and rear-drive vehicles. –  mac Aug 21 '13 at 14:55
    
"Front Wheel Drive cars - This is a tricky situation, because it is natural to assume that the wheels that have to do the pulling (front wheel on front wheel drive car) should have the best traction. The natural assumption is the wrong one and the likely reason that the installation of two new tires is done wrong on so many front wheel drive cars." ajforeignauto.com/… –  endolith Aug 17 at 15:32

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