[SGVLUG] OT: Snow

[Chris Smith]

On 11/17/05, Dustin <laurence at alice.caltech.edu> wrote:
> On Thu, 17 Nov 2005, jmd wrote:
>
> > learning to drive in snow country i was taught a few tricks. when
> > accelerating do so slowly, if you tires begin to slip, back off. once
> > traction is broken start again. this is also true with braking. brake
> > slowly. if your tires lock, you have very little friction stopping
> > you. this is the idea behind antilock brakes.
>
> Yes, excellent advice.  This is what I was just trying to say, but said
> much better.  If I'd read ahead I could just have kept my mouth shut.

Actually, I learned a different principle. In southern Ontario you
pretty much can expect to find black ice somewhere along your drive
home, so you have to be a little paranoid. While you still want to be
as gentle on the breaks as humanly possible, the general principle was
to start breaker harder and then gradually let off the breaks. The
reason for this is that places where vehicles break, intersections in
particular, tend to have ice (and often black ice), thanks to the
polishing/melting/refreezing effects of everyone breaking (yes, kind
of a self fulfilling prophesy, but still). So, while you may have
traction early on, you should assume you are going to lose it
somewhere along the line. With luck, and assuming you've provided
yourself a significant buffer between yourself and the car (or
intersection) in front of you, you have pretty good odds of hitting
snow at *some* point along the way, but the closer you get to said
car, the more the risk is that you got nothing but ice between you and
it. The idea then is to be as close to a complete stop as possible as
you get near the car in front. So you start breaking harder than you
need to to stop in time, easing up slowly as you get closer. With
luck, because you are slowing down and easing up on the breaks, if you
didn't start sliding at the beginning you'll keep getting better and
better odds against sliding as you come to a stop. If at any point you
start to slip let go entirely to regain traction and then repeat the
process. So, this way, your risk of slipping is mostly up front, when
you have the most space/time to come to a complete stop.

> > when approaching a bridge remember while the roadway may not have ice
> > on it, the bridge may be iced over. you'll see signs stating this.
>
> Yah, totally forgot to say that too.  This is a great place to learn what
> "black ice" is the hard way (I didn't say what it was--you can get a thin
> transparent layer of glaze ice that is slipperier than packed snow but
> looks like bare pavement.  This especially happens when you're getting
> slight melting during the day and freezing again at night.  Really, really
> dangerous.

You also want to know the surrounding terrain as well as possible. The
big one is to know whether there is a nearby body of water. Wind tends
to be "helpful" when it comes to black ice too. I don't know why, but
I've also found that places where the road both bends and dips (even
slightly) seem to be great hiding places for black ice.

> > if you do slide let off the gas, the vehicle will correct itself in
> > most circumstances.
>
> OK, this I disagree with unless done very gently.  The problem is that on
> ice if you let up on the gas the engine will break the tires free.  In a
> FWD car you tend to slight straightish, but without any control
> whatsoever.  In a RWD car you also lose all control, but may be spinning
> end for end as well.

Oh, you'll spin just fine even in a front wheel drive car. It just
depends on which wheels retained traction longest. I would mostly
agree with you about what to do when you start sliding. If you know
what you are doing, when you *first* start to feel the loss of
traction, it is helpful to let off the gas and breaks. If you are
spinning or aren't pointed in the right direction though, just lock
the breaks and pray. The good thing about locking the wheels is that
your car will basically go with it's existing momentum (unless a wheel
catches on something), which is primarily in the direction you wanted
to go anyway. I've spun out in snow *on the freeway, in traffic* maybe
3 times, but my vehicle never so much as left my lane, which
dramatically improved the outcomes (no accident in all cases).

> Accelerate *gently*, ease up *gently*, and apply the brakes *gently*.
> If you need to act quicker than that, you're driving too fast for
> conditions.

Good advice, I'' add on to this is if you don't have anti-lock breaks,
don't try to do the stupid "pump the breaks" thing for any reason than
to signal the car behind you that you're in distress. It's kind of the
worst of all options. If you aren't used to snow/ice or you feel
yourself panicking, you're probably best off just locking the breaks
(mostly for the same reasons listed above). If you really know what
you are doing, and you've managed to maintain your piece of mind, go
for threshold breaking, but don't forget to look in your rear view as
the vehicle behind you likely isn't doing it (honestly, when slipping
on ice, I've never had the presence of mind to do threshold breaking
*and* look in the rear view mirror).

--
Chris