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Advantages of AWD in snow?
- Thread starter murphysf
- Start date
Nobody in the thread has mentioned VSA/stability control yet - and active stability control will definitely break traction under engine braking conditions.
I don't know of any civilian AWD/FWD platforms that re-map the stability control based on which wheels are driven. (There may be some I guess, if anyone knows of one, do let know).
One of the places I *really* like having AWD is in crosswinds on frozen pavement - like when crossing the Tydings bridge over the Susquehanna (read: every NE trip).
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Here's a nice little video from two weeks ago on I-70 that highlights the importance of tires over the number of drive wheels:
Seeing 4x4 and AWD vehicles wrecked on I-70 is just another snow day in the Colorado mountains.
Anyone trying to get by with all-season or all-terrain tires should have a look at the I-70 Things IM feed to see all the crashes with vehicles that drive all four wheels: I-70 Things IM Feed
Seeing 4x4 and AWD vehicles wrecked on I-70 is just another snow day in the Colorado mountains.
Anyone trying to get by with all-season or all-terrain tires should have a look at the I-70 Things IM feed to see all the crashes with vehicles that drive all four wheels: I-70 Things IM Feed
"Any other driving in the snow tips you'd like to add?"
Yes. Even if you have ABS that prevents locking up your brakes, you will be better able to steer without touching the brake, and if the snow is deep (it is not deep in this video) or if you are in deep sand or mud, you will stop faster with the brakes locked.
The thing that kills me is that the guy taking the video, it doesn't look like his direction of travel has moved in an hour! What a waste of time. It doesn't even look very snowy...
Yeah this is all great theory but 99% of the population in an emergency can't modulate brakes and steer at the same time because they have no idea what they're doing and they're REALLY focused on not letting their pants get soiled...
There's a reason it was made mandatory in vehicles..probably one of the most important safety features going..
It helps that it's done in the same hydraulic block (or three) as ABS.
Welcome to my life! Fair warning to anyone thinking of moving to CO!
A little color around how this crap happens all the time. It's not much snow, but the roads were warm before the spring storm so a layer of ice formed. CDOT has found it less costly to allow these wrecks to happen and then close the road instead of properly treat the road so they don't happen. It's a lot less effort and expense with this strategy.
As for the stopped traffic, this happens all the time on the tunnel approach in a storm. Hours and hours of wait to get to the tunnel.
Three lanes on the tunnel approach have to squeeze into two tunnel lanes. They need to keep the traffic moving through the tunnel for safety reasons (think fire), so they have metering lights at the entrance. And, they stop all traffic at the top of the hour to allow hazardous materials through the tunnel. That's a lot easier for CDOT than keeping Loveland Pass open during storms like they used to do so hazardous materials can travel where they normally do.
At least we don't have chain control like the OP driving from the Bay Area to Tahoe!
Brake by wire also makes all this magic easier to implement..however uncomfortable that may make people feel! The dichotomy with these technologies is that they're intended for the 1% of time when people have gotten themselves in trouble and are a little panicky. And they work great. If you're trying to have some fun..they trip over themselves. Few of them can actually be overridden in a sensible way..probably never will be able to through legit means..the safety wombles will make sure of that. However, on the whole, probably for the better.
The dichotomy with these technologies is that they're intended for the 1% of time when people have gotten themselves in trouble and are a little panicky. And they work great. If you're trying to have some fun..they trip over themselves. Few of them can actually be overridden in a sensible way..probably never will be able to through legit means..the safety wombles will make sure of that. However, on the whole, probably for the better.
Yeah we occasionally have similar situations..hwy 401 is probably one of the busiest in NA. Slightly warm road..incoming cold front..snow lands, melts, then freezes after a bit. Our highway gang don't send the salters out beforehand..and if you time it poorly, you have a skating rink in the middle of rush hour with 100k cars trying to go through. Disaster.Welcome to my life! Fair warning to anyone thinking of moving to CO!
A little color around how this crap happens all the time. It's not much snow, but the roads were warm before the spring storm so a layer of ice formed. CDOT has found it less costly to allow these wrecks to happen and then close the road instead of properly treat the road so they don't happen. It's a lot less effort and expense with this strategy.
As for the stopped traffic, this happens all the time on the tunnel approach in a storm. Hours and hours of wait to get to the tunnel.
Three lanes on the tunnel approach have to squeeze into two tunnel lanes. They need to keep the traffic moving through the tunnel for safety reasons (think fire), so they have metering lights at the entrance. And, they stop all traffic at the top of the hour to allow hazardous materials through the tunnel. That's a lot easier for CDOT than keeping Loveland Pass open where hazardous materials normally travel like they used to do.
At least we don't have chain control like the OP driving from the Bay Area to Tahoe!
- Joined
- Dec 17, 2015
- Posts
- 4,562
Most of this true. However, in deep snow a locked/skidding tire creates friction and turns snow to ice under the tire. Pumping the brakes or power braking allows the rolling tire to gain what little traction there is again. It worked in log trucks on a greasy beaver slide fwiw.
All Subaru systems explained...Yeah you can find good explanations online if you google around a bit. I've forgotten all the permutations for Subaru. I DO know the 3.6R has a nice 45/55 F/R constant split. It's a very very nice system to drive. Predictable, fun. However, because it's 100% on, bad mileage. To each their own.. Choose wisely.
Yes it is too true. If you talk about how physics happens in a text book then you are correct, if you talk about what happens out there in the snowy, mountainous real world, it definitely matters.
By deep I mean deep enough for the tire to dig a trench and get more traction from digging down and pushing the snow in front of it than there is from the snow it would be rolling over. Of course you can't steer while doing that, so you have to alternate.
I've spent some time in the real world, but I'm not sure what you're saying. Are you saying I will have better luck getting up that icy hill with a one-wheel drive car (standard differential), than with an AWD or a four wheel drive car?
There is a lot of discussion around traction that I read and simple physics doesn't encapsulate the actual conditions very well. And it generally turns into a semantics argument. For instance, theoretical physics would tell you that a motorcycle can't corner at any more than a 45d lean angle. And yet, they regularly achieve greater angles than this. The simpler terms of physics assume a constant or regular value of mu (friction) but tire compounds and behaviour at the road interface are not entirely understood. And traps are laid...
My statement is that AWD in the REAL world "increases" traction. I'm talking about accelerating, steering, assending, descending, braking, all of it works better with 4WD/AWD. Is there lterally more traction at a tire if that tire is connected to an AWD system? Of course not, but I'm not driving a tire, I'm driving a system that includes some tires. Yes, I drove old school RWD and FWD, I now have old school 4WD on my F-250, and BMW's X-Drive on my wife's X5. Both are far superior to any 2WD system. Are they better when driving straight and smooth on the packed? No. They are better at the edges of conditions or good behavior. Appropriate tires and driving skill (intelligence) trump the number of driven wheels. The key is maximizing the use of the tools at hand. 4WD/AWD gives more tools and more margin of error...if intelligence keeps one from taking your more capable vehicle to its limits, then you are almost as bad off as if you took your 2WD vehicle to its limits.
OK then, we agree.
Fixed it for you! I can assure you that the folks who design motorcycles and motorcycle tires do not rely on over-simplified physics, but they do rely on physics. It's science, not magic (although it might seem like magic).