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Old 03-30-2021, 05:05 AM   #1 (permalink)
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FWD vs RWD for snow and ice

I thought I'd make a dedicated FWD vs RWD (vs AWD) thread instead of hijacking other threads with the topic.

The main thing to keep in mind when comparing the two is where is the center of gravity? Is there more weight on the front end or more on the rear? And if so, how much more? Also how high up is that center of gravity?

The first concept that needs to be considered is oversteer vs. understeer. Oversteer is when the rear wheels break traction first. Understeer is when the front wheels break traction first. They are called oversteer and understeer because they do just that, either make the vehicle steer more than what you asked for or not steer enough. Oversteer, if let out of control, can have you going in circles (doughnuts) down the road and you can end up off the road in any direction, such as backwards or sideways. Understeer can make you go off the road straight head-on.

Now most people atribute understeer and oversteer solely to the powered wheels. You hear a lot of people talk about "torque steer" for an example. But that's only a small part of the equation. True, give the vehicle too much throttle (accelerator, gas, etc.) on a slippery enough surface and the drive wheels will break traction. But a lot of times people end up losing traction is when cornering, decelerating or even braking. So how do you get oversteer or understeer when that happens?

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. That's because the wheels that have more weight also have more momentum. Ever gone sledding sitting up and you inevitably end up backwards? That's because your upper body is making the sled have more weight in the rear than in the front. Since it has more mass it has more momentum. The front of the sled may turn just a slight bit but the rear will want to go straight. Next thing you know you're sledding backwards and your sled stays that way since it's easier for the light part to follow the heavy part.

The same thing happens to cars. Regardless of which wheels power the vehicle, having a bit more weight in the rear will naturally cause a bit of oversteer. Having a bit more weight in the front will naturally cause a bit of understeer. And generally speaking, the more weight you have over one axle than the other the more the effect. This is why many FWD vehicles are known for their understeer especially in icy conditions. They have a lot more weight on the front tires than the rear ones so the car tends to go straight. But drive on snow and ice in a mid engine or rear engine vehicle (more weight on rear axle) and you will find the rear will tend to slip out first even if you are coasting in neutral.

Certain weight and drive wheel configurations, however, can cause oversteer in some conditions and understeer in others. Like those front engine, RWD vehicles. Since the rear wheels have the engine torque applied to them they can lose traction due to acceleration on ice. But when when not accelerating, the car on ice may actually understeer due to greater weight over the front axle. Then try engine braking on ice and you start oversteering again.

Another thing that can cause a change is if the weight difference between the rear and front axles is extreme. For an example, a vehicle with a lot of weight on the front may actually tend to oversteer unless coasting or slightly accelerating. I've had this happen a couple times. Once was in an old pickup with a snow plow attached and in the 2WD mode. The vehicle tended to oversteer all over the place except under light acceleration. Also in another pickup coming down a long steep windy snow packed and slick road the truck would keep going straight even with the front wheels turned all that they could until I tapped a bit on brakes. Then the weight would shift enough onto the front wheels that they would suddenly grab and even at such a slow speed the rear of the truck would suddenly whip around.

Now that same principle can apply to vehicles with way too much weight on the rear. The vehicle will tend to understeer, especially under acceleration, but as soon as you let up on the accelerator your vehicle can suddenly go into an oversteer situation.

Even though too much weight on the rear is different that too much weight on the front, the effect is pretty similar. It all really depends on how much of an extreme is the weight difference and how high up off the ground the center of gravity is in relation to the wheel base. A higher profile will amplify this effect even more.

So obviously you want a vehicle that has a weight distribution that's nearly 50:50, or not a whole lot of weight difference between the two axles, and that doesn't have a high center of gravity, at least not for driving very fast on snow and ice. Of course there are still pros and cons to this. One is that a low center of gravity gives you less ground clearance to get over deep snow. Another is that you get less traction under acceleration if your drive wheels don't have much more weight that the non-drive wheels. You could make the case that you're not supposed to drive fast in the snow anyhow and so if you're going to be putting around slowly you might as well as have a lot of weight over the drive wheels in a 2WD (think VW Type1). But then again for today's driving, a low center of gravity 2WD car with about 50:50 weight distribution is still desirable and practical. Why?

The thing is that a lot of people are overly concerned about not getting stuck. So they think that a high ground clearance, AWD or a lot more weight over the drive wheels in a 2WD is very important. But the thing of it is is that getting stuck isn't usually life threatening. And usually with some good tires and some careful driving you can keep from getting stuck in just about any vehicle. If you are stuck you usually can get out of the vehicle and assess the problem and fix it. Maybe you need to shovel a bit of snow from out from under the vehicle. Maybe you need to carry around some sand in the trunk, bed or cargo area that you can pour in front of your tires. Maybe you need to throw on some tire chains that will not only help you get unstuck, they'll help you corener and brake from there on (and now you're better off than all those AWD vehicles without chains).

The real question is how is the vehicle going to react when faced with an emergency during the winter? Maybe someone or something has pulled out in front of you. Maybe you didn't anticipate the road being so slick and you come into a corner a bit too fast. Now what? Regardless if you have AWD or not, if you have a high center of gravity vehicle, especially with an extreme weight difference between front and rear, next thing you know you'll be out of control. Ya, contrary to those commercials, driving those SUV's and pickups fast in the snow and ice is a bad idea. (PS. Rule of thumb is to drive 2/3 the speed limit when it's snow packed. Black ice needs even slower speeds.)

The thing about a vehicle with slightly more weight in the front, like a FWD, the vehicle will 1) react best to the natural reaction of letting off the accelerator and 2) if you do slide off the road or into something you will be going straight ahead into it. Another benefit of having a FWD is if you do get stuck you have a better chance of getting unstuck since your drive wheels are steerable.

But what if you have a bit more weight in the rear or miscalculated the throttle in any RWD so as to cause an oversteer condition. Actually for the professional driver a bit of oversteer is desirable, even in icy conditions, since you still have control of the wheels that turn the vehicle. The problem is that most people, even many who have had years of experience driving in the snow and ice, don't always know how to countersteer and properly correct an oversteer condition. They either end up going in loops or over correct and swing the rear out the other way.

So what's better, RWD or FWD? (Or more front weight or more rear weight?) The best for the inexperienced is a FWD with a bit more weight on the front, like FWD vehicles usually have. And an experienced driver who knows how to properly countersteer an oversteer will do just as well, and in some cases a little better, in one of those or a RWD with just a bit more weight in the rear than in the front. (For an example, put sand bags in the trunk of your RWD.) And if you stick to very slow streets and roads, a 2WD vehicle with even more weight over the drive axles could be appropriate.

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Old 03-30-2021, 07:27 AM   #2 (permalink)
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My RWD experience is pretty much all pickup trucks. I hate trucks. I'd love to play around with a good RWD platform in slick conditions.
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Old 03-30-2021, 08:35 AM   #3 (permalink)
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The only time I've had an issue in the van (rwd, front heavy) was when I come into a turn too hot, but coasting through through the turn usually gets me through it. With the Mercury my problem was ground clearance in the only snow storm I've driven it in. They plowed the main road, but not the cross streets. However, the snow from the main road made a snow wall that my car couldn't clear. I had to keep momentum up and plow through it to not get stuck. Happened multiple times while I was in town. Ironically the wind blew all of the snow off the road once I was out of the city (and there wasn't any trees alongside the road).
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Old 03-30-2021, 10:22 AM   #4 (permalink)
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How do you drift a FWD around a tight corner on a dirt track?
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Old 03-30-2021, 01:19 PM   #5 (permalink)
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Quote:
Originally Posted by M_a_t_t View Post
The only time I've had an issue in the van (rwd, front heavy) was when I come into a turn too hot, but coasting through through the turn usually gets me through it. With the Mercury my problem was ground clearance in the only snow storm I've driven it in. They plowed the main road, but not the cross streets. However, the snow from the main road made a snow wall that my car couldn't clear. I had to keep momentum up and plow through it to not get stuck. Happened multiple times while I was in town. Ironically the wind blew all of the snow off the road once I was out of the city (and there wasn't any trees alongside the road).
In commercial driving school we were taught to slightly accelerate through corners to keep stability. Of course this was because usually we had more weight in the rear than in the front when loaded. That puts more traction over the wheels that normally lose traction first.

When there's more weight in the front then coating is the right reaction. That puts more traction on the front where you'd normally lose traction. Plus with a heavy front RWD you're prone to be thrown back into an oversteer with accelerator input.

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How do you drift a FWD around a tight corner on a dirt track?
Changing where the weight is can help since a lot of weight in the front tires can cause the vehicle to go into an oversteer. But another part of the equation is that the way the suspension is tuned can have an effect of what losses traction first too. Different tires on the front and rear can have a big effect too. Then there's the hands brake. And of course driver technique. Although I'm not entirely sure how they do it since I've taken classes on street driving, not racing.
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Old 03-30-2021, 03:24 PM   #6 (permalink)
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But another part of the equation is that the way the suspension is tuned can have an effect of what losses traction first too.
Drifters popularized extreme camber.

As I see it (owning both), with RWD you can steer with the throttle. With FWD you use the steering wheel to seek for traction.

I'm uncomfortable with high-speed sweeping bends in the XFi. I'll try coasting.
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Old 03-30-2021, 07:31 PM   #7 (permalink)
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Originally Posted by Isaac Zachary View Post
You could make the case that you're not supposed to drive fast in the snow anyhow and so if you're going to be putting around slowly you might as well as have a lot of weight over the drive wheels in a 2WD (think VW Type1). But then again for today's driving, a low center of gravity 2WD car with about 50:50 weight distribution is still desirable and practical.
Makes me want to take a Gurgel BR-800 or a Supermini to the mountains and try its handling on snow


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Another benefit of having a FWD is if you do get stuck you have a better chance of getting unstuck since your drive wheels are steerable.
It has saved me at least once while driving a Dacia Logan through muddy terrain.
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Old 03-30-2021, 09:55 PM   #8 (permalink)
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Makes me want to take a Gurgel BR-800 or a Supermini to the mountains and try its handling on snow

https://i246.photobucket.com/albums/.../halfTrack.jpg
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Old 04-02-2021, 01:53 AM   #9 (permalink)
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Wouldn't a set of tracks count as a cheating device?
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Old 04-02-2021, 03:30 AM   #10 (permalink)
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Wouldn't a set of tracks count as a cheating device?
No. Definitely not. We need more innovation. Tracks, rockets, gyroscopes, sails and propellers are all welcome.

AWD is great, but it only helps you accelerate. Maybe make 6 wheeled cars? Tracks seem pretty great. Like I said, I loved driving vehicles with automatic tire chains. Anything that can be tried and improved upon is better than the one-size-fits-all SUV world we live in today.

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