From: ross@prpa.philips.com (Ross Morley)
Subject: Re: Do I need Chains?
Organization: Philips Research Palo Alto
Distribution: ca
Date: Fri, 18 Dec 1992 19:35:21 GMT

grant@clarinet.com (Grant Robinson) writes:

>Yes, even the ones with chains on.

I guess you can do that on snow. On hard pavement I wouldn't want to.
I guess we're getting sidetracked a bit (that's O.K.) - my original 
posting was about being made to use on hard pavement. Now THAT wears 
the chains (and tires, I suspect) out fast.

>For the number of times most people use chains, I doubt wear is a concern.
>People who drive regularly in those kind of conditions probably have M/S
>tires and 4WD.  As for them breaking, I imagine it's a liability type thing,
(stuff omitted for brevity)

I'm sure you're right.

>>Now I would have been one of those 4WDs pushing 65 if I felt
>>sufficiently in control :-). 

>I drove a 4WD truck in Canada for the last 4 years, and the important
>thing to remember is that although they get better traction, they don't
>stop any better.  

Agreed. I'm well aware of this. Of course the road would have to be
straight and level and have traffic very well spaced. I always test my
stopping power now & then on straights when there isn't traffic close
by, by gently touching the brakes to see if I lose traction. Once I do
I can immediately release the brake to regain it. This way I have
confidence that I have a certain amount of stopping power, and if it's
not enough I slow down. Don't try this on a bend!

> In fact with many 4WD's once you lose traction, they're
>one of the worst places to be, because of the extra weight and poor
>emergency handling.  

With this I disagree. 4WD definitely helps recovery from a skid, and 
generally improves handling in cornering. This has been very well 
proven in road rallying. The extra weight only improves traction.
4 wheel engine braking also allows you to slow down better without the 
sudden bite of brakes.

Two examples from my own experience:

While driving my front-WD Celica in Oregon one thanksgiving after a
freak early snowstorm (I didn't have chains) I simply removed my foot
from the accelerator on a straight, and found myself in a spin. No
brakes were applied. That car is front-WD and very light in the rear,
so it just broke away. I wasn't even running in low gear at high revs -
this was gentle engine braking. I wasn't going very fast (maybe
~30mph). Never had this trouble with 4WD.

Recently in my 4WD I took the corner from 88 into Kirkwood (on snow) at
a speed I wouldn't have done it at in a 2WD. Traffic was light, BTW.
Speed around 20mph, no braking. I skidded a bit, but the nose kept
pointing in the right direction and a little power pulled me around the
corner, even while sliding sideways a bit. There was no tendency to
spin out. Now I've seen plently of rear-WDs spin out in similar turns.
4WD just makes it so much easier to stay in control. 

If you ever followed the world road rallies a few years back when Audi
first introduced the full-time 4WD Quattro, you'd realize how that
revolutionized rallying in slippery conditions. The other cars didn't
have a _chance_ on snow or unpaved sections! On pavement it didn't make
much difference. The following couple of years saw the other major
compeititors introducing 4WD, starting with Toyota. Since then many
manufactureres have been making cars all wheel drive. It DOES make
handling much better and safer (though one must not think that one can
drive as if on dry pavement!). By the way, the drivers commented that
driving the 4WD is rather boring 'cause you just point it where you
want to go and it goes there. With 2WD (rear) they have to break
traction at the rear and apply power and maintain a delicate balance
with the rear skidding - much more fun if you're a rally driver, but
not so safe for the average joe. So 4WD is easier and faster. It looks
much less dramatic, but actually takes the corners much faster.
Now I DON'T advocate testing your rally driving skills on crowded I80!
I only mentioned rallying to show how 4WD improves handling and safety.

But I agree about braking - all cars have 4 wheel brakes anyway and 
a sudden bite can break traction. This is where antilock brakes 
can really help, especially in the rear as a rear breakaway can 
throw you into a spin. I have both 4WD and rear antilock.

>I'm not sure 65mph is out of line on the straights, provided you double or
>triple your space cushion.  As for corners, my advice would be that it's a
>lot easier not to start sliding (ie go slow enough) than to stop sliding,
>once started. :)

Agreed. I'd say even quadruple your cushion.

dhepner@cup.hp.com (Dan Hepner) writes:

> Nor do they handle any better, or corner any better, misleading ads
> to the contrary; 

See above.

>  in fact the only they do better on packed snow is
> accelerate.  (From the kind of serious experimentation most of us
(some lines omitted for brevity)
> realize that if the wheels are spinning, letting off of the pedal
> might be appropriate.  

That is actually a safety feature, as accelerating with 4WD can pull
you around a corner where just releasing the brakes will leave you
sliding sideways. That's if you get into a skid. Better not to.  I'm
talking about slippery snow, ie. packed. Soft snow is not all that
slippery, so 2WD can handle O.K. (if it can move at all).

>  Ads showing 4WD as a safety feature when
> on wet blacktop are just plain bogus.

Not true. Rallies have proven 4WD corners better in slippery
conditions, even on pavement.

Ross

-- 
Ross Morley                   .---.     email:  ross@prpa.philips.com
Philips Research Palo Alto   |  ___\    Phone:  (415) 354 0325
4005 Miranda Ave, Suite 175   \/    \   FAX:    (415) 354 0309
Palo Alto, CA 94304           ^^