FWD vs RWD for snow and ice

[Piotrsko]

Issaac Zachary:How do YOU keep the auto chains from winding up on themselves in a freezing slush or keep them under the wheels on hard icy mornings? I hated the auto chains on my school bus, I would install regular chains on the outsides on sloppy mornings, but I had union approval to install and remove them.

[Isaac Zachary]

Originally Posted by Piotrsko

Issaac Zachary:How do YOU keep the auto chains from winding up on themselves in a freezing slush or keep them under the wheels on hard icy mornings? I hated the auto chains on my school bus, I would install regular chains on the outsides on sloppy mornings, but I had union approval to install and remove them.

Here in Colorado, at least the part where I live, freezing slush and hard icy morning are not common. Autochains are useful going over steep snow packed mountain passes. Instead of stopping at the base and putting them on, driving a mile, pulling over and making sure they're still tight, then taking them off at the bottom, then doing it again at the next pass and so on, you just flip the switch and off you go.

My main problem with autochains was in deep snow they wouldn't spin around. Regular tire chains are better overall and work in some cases autochains don't. But having to pull over and throw on and off chains for a 35,000lb vehicle all the time is not easy.

I suppose if you live in a town or City where your entire route can be driven at speeds of 30mph or less then putting on a set of chains and leaving them on would work. But here towns are very small and nearly all the bus routes include going down two lane highways. It's already bad enough to come up on a school bus that's going slower than traffic and no way to pass it. It's much worse if that part of the highway is dry and the bus is going 30 in a 65mph zone just because the driver put her chains on beforehand so she wouldn't have to once she got off the highway onto the rural roads.

[cRiPpLe_rOoStEr]

Originally Posted by Isaac Zachary

Tracks seem pretty great.

Sure, but they're somewhat specialized, and more suitable to a strictly off-road use.

Anything that can be tried and improved upon is better than the one-size-fits-all SUV world we live in today.

No doubt about that.

[MetroMPG]

I think computerized controls (traction control & stability control) have allowed for the revival of the popularity of RWD vehicles among unskilled drivers in climates that get regular snow/ice in the winter.

As much as I am an advocate for better driver training, I'm also a realist. Licensing (where I live) is pretty lax. Training for new drivers is encouraged but optional. Specific training for driving in low-traction conditions is almost unheard of. Never mind refresher training for already-licensed drivers. I love to drive, so I've taken & taught all of the above.

I'll admit I'm rusty on RWD, simply because I rarely drive it in slippery conditions. (The MPGiata is only the 3rd RWD vehicle I've owned, and it's a fair-weather-only car.)

But, as much as I get annoyed when modern electronic nannies interfere with managing my own yaw & slip angles (always stepping in too soon for my liking), in general I think the more technology we throw at this, the better. Incentives & laws for winter tires help, too.

Any other aficionados of winter driving dashcam driving compilations out there?

I get a kick out of identifying the clips where it's clear to me some driver's bacon has just been saved by their vehicle's stability control, helping them prevent or rein in a scary tank-slapper situation.

I bet if we did a statistical analysis of the number of cars (FWD or RWD) oversteering into ditches in those videos, we'd find they're mostly older vehicles lacking the computer safety nannies.

Maybe the days are numbered for winter driving crash compilations?

[Piotrsko]

Here in Reno, we get partial thaws and overnight re-freezes. Most of the yahoos in the ditch are young people driving new $$$$ AWD stuff in way too much of a hurry. Traction control is nice but doesn't help on wet ice or when there is not traction to be obtained.

[MetroMPG]

Originally Posted by Isaac Zachary

You might think that the wheels with the most weight will have the better traction making the other two tires lose traction first. But that's not always true. In fact, a lot of times it isn't.

As a youngster, I was slightly disappointed the first time I drove a Nissan 240 and 300 (RWD both) on a skidpad: we were circling at gradually increasing speed, I was expecting (hoping for) oversteer as the tires passed their traction limits. But the fronts always let go first, leading to understeer.

[Isaac Zachary]

Originally Posted by MetroMPG

As a youngster, I was slightly disappointed the first time I drove a Nissan 240 and 300 (RWD both) on a skidpad: we were circling at gradually increasing speed, I was expecting (hoping for) oversteer as the tires passed their traction limits. But the fronts always let go first, leading to understeer.

I could be wrong, but those look like their front engine vehicles with more weight on the front. Hence the understeer. Accelerating can make it worse, unless overpowered.

That's the way a lot of these cars work. Slightly accelerating or decelerating can cause one condition and slamming on the throttle or brakes another condition, as long as there's enough power (braking or accelerating). It's when people that make abrupt changes that things can go out of control.

I noticed the Teslas have a bit more weight on the rear than the front, but are close to a 50:50 weight distribution. I suppose that's what we're going to see from now on. With the weight near 50:50, even if there's slightly more on the rear than the front, it's much easier to maintain stability and for stability control to work.

But on the other hand, a car with 60 or 65% of the weight on the drive wheels will have better traction from a stop than a car with around 55% on the drive wheels. Of course accelerating in RWD will help, but only once the car starts moving and if you're accelerating forwards. A car that's stuck won't get the weight shift onto the rear wheels because it can't accelerate.

The problem with a car with 60-65% of the weight on the rear wheels is that potentially nasty oversteer even when not touching the throttle. The correct procedure through corners in such a vehicle is to slightly accelerate and to be smooth in your transitions from braking to cornering to accelerating. But most people in a pickle from coming too fast into the corner will naturally try to instantly decelerate, which is better if you have more weight on the front.

Maybe someday we'll have invented vehicles that can move the wheels forwards and backwards, depending on the circumstances.

[JSH]

RWD always - Dry, wet, snow, ice. Give me a RWD car with 55 - 60% of the weight on the rear axle. Hard to do with a combustion car and still have usable storage but very easy to do with an EV.

Why RWD? It is better for vehicle dynamics. In a FWD car the front wheels are doing double duty - steering and moving the car. If a driver applies too much power or brakes in a FWD car they lose traction and steering.

Also a FWD car shifts weight off the drive wheels when accelerating or going up a hill.

Why rear bias? Again it helps vehicle dynamics. Under acceleration weight transfers to the rear axle increasing available grip. (good for RWD / bad for FWD) Under braking weight shifts forward and more equally loads the tires compared to a vehicle with a forward weight bias. Cars with heavy front axle bias like many FWD cars and unloaded pickups shift almost all their weight to the front axle under heavy braking. The rear tires have almost no load and can't provide much braking.

Understeer vs Oversteer:

Understeer is more dangerous. The one good thing about understeer is that if an novice driver freaks out and does nothing when the front end looses traction the car will eventually self recover. That is the only good thing. The big downsides are that with understeer you lose steering and the front of the car slides.

Say you are going around a corner and apply too much power or brakes and the car understeers. On a right hand curve the car will drift into oncoming traffic - boom head on collision. On a left hand curve the car drift off the road and onto the shoulder were grip is much less than on the road.

With oversteer it is the rear end stepping out. The driver still has steering and when the vehicle recovers it is still in the correct lane and on the road. Yes, the rear end my slide into out of the lane temporarily but if the driver responds correctly it comes back inline with the front almost on the original path.

Finally worst case scenario and I completely lose control - I would rather be going off the road or into oncoming traffic backwards than frontwards. Crumple zones are huge on the rear of a car and the collision force will drive you back into your seat - spreading the impact over the entire body. With a forward collision the force is concentrated just along the seatbelt and the head suffers whiplash.

The best handling car I've ever owned was a 1972 Porsche 914. Not much power but SO much grip.

The addition of stability control only even further helps the case for RWD. The car will attempt to correct the skid itself and reacts almost instantaneously to the lose of traction. In early 2020 I had a BMW 330i as a rental during a couple day snowstorm in North Carolina. Even on all-season tire the car did great. No issue with traction accelerating and stable braking. I got a good indication of how much stability control can do when I went to an empty parking lot and tried to so some donuts. Standard mode I could barely get any wheelspin. Turn off traction control and I could spin the rear wheelsl as much as I like in a straight line but the car absolutely refused to allow me to do donuts. It would let the rear end come out 30 - 45 degrees but then the stability control came on, straightened out the slide, and ruined the fun.

[Isaac Zachary]

I don't buy the whole "you need better acceleration for winter" theory. Sure, RWD for the summer makes sense if you're into the whole sports car thing, especially if you hit the track from time to time. But in the winter you're supposed to take things nice and easy anyway. I'm not impressed when some impatient jerk goes on a passing spree on glare ice just because he can. On snowpack the speed limit is automatically 2/3 of what it is when dry. 60mph becomes 40mph. Do I really need a car that can take off like a rocket for that kind of driving? (Ask me how many people I've seen passing everyone else in the winter and farther ahead they're rolled over into the ditch.)

Going up hills kind of makes sense. But on the other hand, if it's pretty hard to make it up it even in a FWD you probably aren't going to want to come back down it in any wheel drive. Still, I rarely have problems with hills in my FWD. Sure, I can't blast up them like a maniac driving an AWD or RWD. But I usually have no problem keeping a normal speed.

Also the whole "rear axle won't have any weight on it while braking" doesn't really apply in modern FWD, especially on snow and ice. That's because first of all, modern cars are closer to a 50:50 weight difference than every, and you can't slow down enough to get as much weight transfer as you can in the summer. Even with the best winter tires (which are not approved by the DOT for highway use) your stopping distance on snowpack is at best 6 times longer than on dry roads on summer tires. In other words you have at best 1/6 the weight transfer in the snow, allowing the rear wheels to still do plenty of braking even in a FWD.

Thinking that if you lose control in a RWD you'll crash backwards isn't realistic. You're more likely to crash sideways. Doors usually don't have as much as a crumple zone as the front end.

I can agree that for me personally I prefer the driving characteristics of a moderately oversteering vehicle. You do have the possibility of keeping control of the vehicle. There were plenty of times I was driving near sideways in my school bus but was still able to keep control of it since the front wheels still had traction. I hate to say it, but most drivers don't seem to know how to drive in the snow. Sure, you'll find FWD cars stuck in parking lots where they hadn't plowed the snow yet. But the great majority of vehicles that go out of control and end up smashed and flipped over are not FWD cars.

[JSH]

I want better driving dynamics in all conditions. Wet and snowy roads just reduce the coefficient of friction in reduce the speeds at which tires lose traction.

I don't drive like a maniac on snow but I like knowing I have a bigger margin of error.

I can't think of any FWD cars with 50:50 weight distribution. Front / Rear balance isn't something on the manufacturer's spec sheet for some reason but some random FWD cars I found:

2007 Toyota Camry Hybrid 57% front / 43% rear.
VW Golf Sportwagen 57% front / 43% rear.
VW GTI 61% Front / 39% Rear.
2016 Dodge Caravan 56% / 44%