Moraff . . . And just my mechanic's two cents worth... he says he'd put the new tires on the front if you were to do only two of them (which he disagrees with for the reason I stated) as while it is true you wouldn't want the back end to break away in a stop... not being able to steer is probably going to me much more of an issue.
Compromised . . .
my mechanic . . . suggests regular rotation and I agree with him to replace tires as a full set of 4. If you are going to cheap out, he always puts the new tires on the front.
These mechanics should be struck off! Their advice (to put the new tires on the front) can kill you! They should stick to their trade, and not try to pretend to be theoretical engineers.
But surely it stands to reason, doesn’t it, that your best chance of retaining steering control is to keep the front wheels from locking, and the best chance of achieving that is to put the new tires on the front? Wrong.
Go to
www.michelinman.com/tire-care/tire-basics/ Click on “Where should you put two new tires?”, and watch the video.
Here’s the engineering answer. Imagine you are going round a corner on a wet road, when some emergency arises, and you apply the brakes too heavily. Take the two cases: (a) your rear wheels lock and skid, and (b) your front wheels lock and skid.
In (a), the front wheels are still rolling, and are still exerting good braking force (from the front of the car), and are still capable of influencing steering direction. The back wheels have stopped rolling, and are skidding, and are therefore exerting only a much reduced degree of retardation and, zero directional control. So now, there is a very large tendency for the back end of the car to swing outwards, on the bend, and to overtake the front of the car. Once it starts, the tendency snowballs. It’s like trying to balance a pencil on its point. You completely lose control of both retardation and direction.
In (b), the back wheels are still rolling, and are still exerting good braking force, and are still capable of influencing steering direction. The front wheels have stopped rolling, and are skidding, and are therefore exerting only a much reduced degree of retardation, and zero directionality. So now, the main directionality and retardation forces (such as they are) are coming from the back of the car, not the front. So the car remains stable, and tends to carry on along a straight line path, but still pointing forwards. Not good of course – but it’s a lifetime better than spinning.
Will your anti-skid system save you? Maybe. But the a-s system is set up primarily to deal with wheel lock under heavy braking, and the system does not work so well under light braking – and light braking is all you get on a wet road. In fact, the more slippery the road, the less effective your anti-skid system is, to prevent the wheels from locking.
The moral is quite clear: Never drive your car so that the wheels lock! But if your wheels do lock, under braking, your chance of losing control and hitting someone is much worse when the wheels that lock are the rear wheels. And you can do something to make sure the fronts lock first – put your new tires on the back!
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