RWD vs. FWD in snow and ice

Get it right -

it's not front wheel drive vs rear wheel drive, it's Weight over drive
wheels

perfect world = mid enigine all wheel drive with good tires selected for the
conditions / terrain.

 

Yes, hard to beat tall, skinny tires in snow and mud. My grandfather
used to tell some amazing stories of where he took his model T. They
had lots of ground clearance and those tires would drop right through
mud and snow (as long as it wasn't TOO deep).


Matt

 

Enough weight on the drive wheels is important. But only if we're
talking about pickup trucks. When it comes to cars, the weight
balance difference is marginal between FWD and RWD.

It's more efficient (effective) for the front wheels on a FWD car to
_pull_ a car through snow vs the back wheels on a RWD to _push_ a car
through snow.

In snow, the RWD car is operating at a disadvantage, and snow tires
will only do so much - never enough to match the capability of a FWD.

When it comes to snows, get the narrowest tires you can put on. If
you have a set of wheels to use in the winter, make them the smallest
size that will fit the car (and then get the tallest/narrowest tires
that will fit and give the same over-all diameter as the oem tires).

 

Not completely. Having the driven wheels also steering has some
advantages, especially at slow speeds. It also has some disadvantages,
especially at higher speeds.

Yep!


Matt

 

Why?


Matt

 

Even rabid RWD proponents admit FWD has the advantage in snow:

http://slate.msn.com/id/2081194/#ContinueArticle

"In snow, FWD cars have a third advantage in that they pull the car
through the path the front tires create, instead of turning the front
tires into mini-snowplows."

Also:

http://chrysler.jbcarpages.com/300/2005/

"One of the advantages of front-wheel drive is traction in snow, but
that too has been erased over the years."

Driving and cornering on hard-packed or ankle-deep snow is one thing.
Getting yourself through a snow drift at the end of the drivway is
another (and that's what I'm talking about).

Here:

http://www.rearwheeldrive.org/rwd/rwdquiz.htm

We see that the quiz questions are stacked in favor of RWD. Note the
absence of a FWD choice in question 1. The authors say in several
places that the extra weight of AWD is a liability, yet propose adding
bags of sand to a RWD car to improve acceleration in snow (question
6). In question 5, they say RWD is better than FWD for cornering in
slipper conditions (because for FWD the front tires must both
accelerate and steer). They don't explain why you'd want to be
accelerating in a turn on a slippery road. They don't ask which type
of drivetrain is better for driving through deep snow at low speeds.

If you hold the view that FWD does not have a slam-dunk advantage over
RWD on snow-covered roads, then I'd like you to find a web site, a
posting, or editorial where the author holds a similar view. I
haven't seen any.

A lot is written about the pro's and con's of FWD and RWD during
winter driving. Much of that is focused on cornering and handling,
and some straight-line acceleration from a standing start. All of
that verbiage is wasted space because the overwhelming majority of
people do not treat winter driving like an alpine auto-cross.

The condition that practically everyone in a winter climate will face
is the occasional need to move the car forward from A to B in deep
snow under very low speeds. By deep snow I'm talking about 6 inches
(on a grade) or more (on flat terrain, parking lot, the end of your
driveway, etc). Other than the first reference (above) I haven't come
across any other reference where the concept of FWD pulling a car
through the snow exists or is different than RWD pushing the front
through the snow. But conceptually, I stand by the concept that the
front tires are snow plows for a RWD car trying to push a car through
snow.

 

Yes all very good points, but again I say that the "Optimum" is mid engine
with all-wheeldrive, 25% weight at each of the four corners. The closer ANY
vehicle comes to this equalized formula the better.

A front wheel drive car with 80/20 weight distribution may get you out of
snow due to weight over the driving wheels but it will be a lot harder to
maintain safe control of than a vehicle with 50/50 distribution - regardless
of road conditions.

Almost if not more important than getting "unstuck" is to be able to handle
the vehicle in a varity of conditions, cornering, braking, accleration,
emergency stops etc. The closer to 50/50 the more predictable a car will be,
in all situations.

The single flaw in FF vehicles is you are asking the same 2 tires to perform
all cornering, acceleration and the majoirity of braking duties.

If you can by any means get more of the tires to perform a more shared
responsibility the your vehicle's actions you will be better at getting
unstuck and staying unstuck.

One last point, if you had a Front wheel drive REAR engine car - would you
still say that front wheel drive is better?

 

I never disputed that FWD has an advantage over RWD, but I believe
almost all of that advantage is due to the weight distribution and very
little is due to the front wheels "pulling" the car rather than the rear
wheels "pushing" the car. I believe it is fairly well accepted that
having the same wheels driving as well as steering will cause the tires
to lose traction sooner than if steering alone (supported by the article
you reference above). The tires can provide only so much traction.
Adding the vector from the driving force to the vector sideways from the
steering force means that the total force vector will exceed the
traction capability of the tire sooner than if the tire was just driving
or just steering. At low speed this isn't much of an issue as the
lateral vector due to steering is pretty small, however, at higher
speeds this can become significant. I'd much rather drive a RWD car at
high speeds in the snow than an FWD. My minivans will out accelerate my
K1500 (when it is in RWD only) at low speeds, but once you get above
about 50 MPH, the truck handles much better in snow. Same with my old
Fury III. It took a while to get rolling, but once up to speed it
handled very well on slippery roads.

For that, momentum is far more important than traction, and either car
will get you through.

The snowplow concept only holds if the tires aren't turning. I've never
seen a car that had enough drag in the front wheels such that the
friction available even on ice wasn't sufficient to rotate the wheels
(obviously, assuming that the brakes aren't being applied). I've seen
nothing to support this snowplow theory.


Matt

 

I've never seen such a car, but I do know that rear engine, rear wheel
drive cars go VERY well in the snow. My father had a Corvair that was
great in the snow and I had two Beetles that were also very good, at
least at low speed. The had great traction, but steering was a
challenge with the light front end.


Matt

 

Karla wrote:

Listen to a police scanner some time. Notice how almost all
transmissions are a matter of seconds? Notice how almost all cell
phone uses are a matter of minutes?? See any difference?

Harry K

 

Excuse me Daniel, is this guy for real???

By his standards then the following vehicles are unsafe and should be taken
off the roads:

Just about every Mercedes
All BMW's
All Ferrari's
All Maserati's (hell, lets just say all Italian sports cars)
Pontiac GTO (2004 - onward) (Had to fit Holden in there somewhere)
etc etc etc

I clicked on your link, but could find no method of sending a reply to Mr.
Macdougall. And he really, really deserves one.

Steve Magee
Newcastle NSW Aust

 

I would argue that your optimum is not really optimum for a car used
year-round for the majority of car owners. It's quite a price to pay
(in several ways) to lug around the extra mechanicals of AWD for the
very few times that most people really need it. AWD is more a
marketing gimic than a well-utilized capability for most.

Sure there is an optimum for traction. I could say a sherman tank is
even better in the snow. Doesn't mean it's ergonomic - or economic.

Which is a totally off-base weight distribution for cars these days

I think too much is made of the weight being over the front wheels.
Your average FWD car today is about 300 lbs lighter than the average
RWD car of 35 years ago. Which is another way of saying that I bet
just as much weight was probably on the rear wheels of the old RWD
cars as are on the FWD cars today.

Which FWD can do on dry pavement to the satisfaction of most drivers.
In the rain, or snow, or ice, people aren't going to be driving like
it's the 24 hours of Le Mans - so why are we talking about the
bleeding cutting edge of tire and drive-train performance in bad
weather when its Mrs. Soccer Mom behind the wheel?

If it means paying $5k more for the AWD option (and the high
maintainence costs and parasitic drivetrain losses) when I'm satisfied
that FWD with snow tires gets me out of the worst situations, you
haven't convinced me that AWD is a logical requirement.

Better than rear-engine, RWD? Yes.

The front wheels pulling you through the snow I think trumps any
additional weight you're going to put on the rear tires so yes I still
think that for deep snow drivability FWD rear engine is better than
RWD rear engine.

I think the weight tranfer thing is more like 60:40 these days (at
worst). They're not putting cast-iron V8's in cars anymore.

 

I have, however, seen ice so slick that the rear tires will spin lazily
(in an automatic) while a car is waiting stopped at a light. So it
might be possible for the front wheels to drag a little when starting
off. Of course that falls under the category of "probably should have
stayed home today..."

nate

 

Just about every Mercedes

You would drive a Ferrari in winter?

 

I certainly would...in Arizona, or California, or Texas, or New Mexico,
etc.

For more severe winter climes, I'd pick one of these Lamborghinis instead:

http://tinyurl.com/4y457

 

With properly-chosen winter tires and a thoughtful, attentive and skillful
driver, RWD works fine. Traction control is not necessary. That is my
experience from many winters in Colorado, Michigan and Ontario.

 

Written like a typical newspaper idiot.

 

Every comparitive review of the new Magnum and 300 in snow says exactly
the opposite. They easily match the performance of FWD with their
traction control systems.

FWD stinks. Always has, always will (this coming from the owner of a
very nice FWD vehicle that has given over 200,000 miles service- but the
balance and handling still stinks compared to RWD).

 

How would the phone conversation differ from merely conversing with
someone in your vehicle, unless the handset had something to do with it?

 

Or at least "should have had those tires studded..."


Matt