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Re: Its all about snow tires... (archive)

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Posted by Roman on December 14, 2000 at 08:16:15:

In Reply to: Re: Its all about snow tires... posted by Joe Ording on December 13, 2000 at 23:07:34:

I knew that downshifting in slippery conditions could have an effect similar to hard braking, but my theorizing wasn't quite on - thanks for your explanation.

Roman.

P.S. Should the two references to tire "spinning" actually read "skidding" or "slipping"?


Downshifting puts a lot of decelerative force on the rear tires. This results in a forward weight shift, unloading the rear suspension and reducing the already-taxed traction of the rear tires. Unless done very carefully and at lower revs, this will result in the back tires spinning. The reason that the brakes are biased to the front of the car is to keep you from locking up the rear brakes. When the rear tires lose traction - either because they are spinning when decelerating or are locked in heavy braking - and the front tires still have traction, the rear end will try to whip around. If you're braking and this happens, you can merely let off the brakes, usually causing enough weight to shift back to the rear to stop the loss of traction. If you downshift into another gear and begin to spin around, it's much harder to catch. I don't suggest even mild downshifting in rain or snow. Just use the brakes, and put the car back in gear when you're ready to accelerate again.

Keeping the car in a lower gear to maintain speed while going downhill shouldn't be a problem, however.


Actually, it's not like stomping on the brakes without ABS, because the deceleration is being provided by the rear wheels only, whereas the braking system is quite biased to the front brakes. More like (if you don't match revs as stated below) pulling the parking brake lever up. I find engine braking a critical technique for maitaining reasonable speed on steep, slippery hills.

Peter


I'm not too sure about your "downshift" suggestion. Downshifting at high revs will cause a braking effect which corresponds to stomping on your brakes without the benefit of ABS. This could result in a spinout.






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