On Tue, 10 Feb 2009 17:57:00 +0200, Eero Ahonen wrote:

> Jim Henderson wrote:
>> 
>> Well, I've only got something like 20 years of experience driving
>> during winters in Minnesota and Utah to call on.
> 
> I only have 10 in Finland :-). Honestly, I have no idea what kind of
> winters there is at Utah or Minnesota, but I assume that means there's
> snow and ice available enough.

Yes, and plenty of it in both places.  Drove into work on ice and snow 
today, in fact - and slid turning into the parking lot at work. :-)

>> It's been my experience that
>> it is generally more effective to downshift and let the engine do the
>> work.
> 
> How could it be? In both styles the negative acceleration is applied to
> the ground via tires and tire/ground -layer being the weakest part -
> with downshifting most cars do it practically via 1 wheel, almost no car
> makes it via 4 wheel (which would mean 4WD with completely locked
> differentials), while brakes are applied via all 4 wheels. Breaking with
> the engine is of course more economical

By downshifting, what happens is the wheels aren't stopped, but the 
torque applied through the drivetrain slows them down as the engine revs 
come down.  This has been my experience in 4 cars, including the first 
car I drove (a manual) - but of course you have to be more careful in a 
manual when downshifting - usually I'd start by just putting the clutch 
in and letting the car coast.  I did actually get to the point with that 
car, though, that I could shift if I needed to without using the clutch, 
just listen to the engine and when it got to the right speed, shifting 
without the clutch wasn't a problem.  I don't know if it's that easy to 
do in newer manual transmission cars, though - that old car was a '74 
Duster, manual *everything*, power *nothing*. ;-)

>> Unless you know with relative precision how slippery it is, tapping the
>> breaks can be a bad prospect.
> 
> There might be a language wall here - I'd consider tapping as a slight
> touch and hitting the brakes as a 'do-not-do' -movement on ice.

It depends on the road conditions.  For example, this morning as I turned 
left into the parking lot at the office, the car's momentum overcame the 
friction of the tires on the ice, and I ended up not turning as per usual 
but sliding instead.  In that case, pumping the breaks was an effective 
way to slow the car down.  Similar effect to a car with ABS (which I 
really miss in my current car, my last one had ABS but the new one 
doesn't), but the pulsing isn't rapid.

If a car has ABS, you can get away with hitting the breaks, because the 
ABS system will prevent the wheels from locking up.

>> I've managed to put two cars in the ditch in 20 years.  One from
>> overcorrecting a spin, and one for not slowing down enough because some
>> jackass was tailgating me.  I've never managed to put my car in the
>> ditch by stepping on the brakes, because I was taught not to do that
>> and I don't. <shrug>  I can't argue with what works for me.
> 
> We have the same ratio, I've put one in 10 years :). That was due to
> lifting the gas pedal while coming back to my lane after overtaking
> another car. And well, that was actually no ditch AFAIK, while the same
> car is still mine and registered (just now out of the traffic, though -
> it's my summer toy).

:-)

> And I'm not saying that braking with the engine doesn't work - I'm
> saying that braking with the brakes works too, it just needs to be done
> carefully.

Yes, and I can agree with that.  The problem is that most people don't do 
it carefully enough, and end up like the SUV I saw on the way into work 
today - wrecked.

>> Yes, that will also work, but yes, it is dependent on knowing the
>> condition of your tires.  I think we both can agree that there is a
>> high degree of situational awareness called for.
> 
> *Everything* while driving on ice is dependent on knowing the condition
> of tires, more or less. As pointed out, RWD can give you a spin (or try
> it) with downshifting, if the road is too slippery. It's always
> necessary to know what kind of tires you're driving on and what's their
> condition. What I ment is that to test the possibilities to brake with
> accelerating you'll need to know the ratio of acceleration traction and
> braking traction of your tires. Eg. I once had tires (Kleber Kapnor 4
> 185/65/15) which were catastrophic when accelerating, but pretty good
> when turning and braking.

We are in violent agreement. ;-)

>> Yes, agreed - the more you can practice in a safe environment, the
>> better prepared you'll be.  :-)
> 
> And the more fun you'll have (while practicing, of course), so it's a
> win-win situation :-).

:-)

Jim

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