Prius in the snow II?

I'm never sure how reliable wikipedia is but (per wikipedia):

So, to me that sounds like it should assist in maintaining control while taking turns faster than without VSC. Unfortunately, it seems that this morning I "pushed the possibilities of the car's chassis and VSC too far". Nothing damaged, nobody hurt, lesson learned.

As I understand it, a car with 4WD engaged is actually more likely to skid and end up in a ditch when turning than a car with 2WD. 4WD makes sure that all the wheels are spinning at the same speed. Great when one or more wheels aren't touching the ground or would otherwise be spinning in mud/snow/ice/sand/gravel while other wheels have good traction, but not good at all when taking a typical turn at typical speeds. When turning, the outside wheels need to spin faster than the inside wheels to maintain a grip on the road (the reason for the differential in a typical 2WD car). If all the wheels are spinning at the same speed, 1 or more of them have to slip to keep up with the others. This reduces traction and makes "ending up in the ditch" much more likely.

 

Typically, a VSC system will at best let you take corners as fast as you are able to without. Very good drivers are able to outperform VSC systems (which usually err on the side of conservative to maintain vehicle control and prevent spins/fishtailing as nerfer explained), but just as drivers vary in their skills, so do VSC systems vary in their ability to drive quickly.

VSC systems usually use a combination of wheel speed sensors, yaw rate sensors and accelerometers to determine what the car is doing, what it thinks the car may do and what corrective actions are needed to prevent spinning and to try to keep the car pointed in the direction it is traveling. This means that the car will typically push (car will turn less sharp than the front wheels are turned) when VSC is activated and you will end up putting the front wheels into a curb on the opposite site of the road as nerfer explained.

VSC will let you attempt to hit the brakes or steer to avoid obstacles to the extent that available traction allows, but if you hit ice where there is next to no traction (and if you slid across the road going around a street corner at 25mph it sounds like you did) there's not a whole lot you can do but pray.

 

Hmm, I'm going to need to investigate this further. Why would I want VSC if it is going to reduce the stability of the car when taking turns? I seem to have misunderstood the stuff I've read about it. I had thought that it would selectively brake individual wheels to help get the car moving in my intended direction of motion (as indicated by the steering wheel). If all it does is rotate the car so it is pointed in the actual direction of motion, then it is more than useless, it is downright dangerous. (I try to steer around some object, and as the wheels start to slide a bit, VSC points the car back at the object I'm trying to avoid?!)

Very interesting, as this is exactly what ended up happening. Car rotated clockwise to take the turn. About a third of the way through the turn, the car started to slide to the outside of the turn. The warning light with the yellow car and squiggly lines lit up, and I head some beeps. The car continued to slide at an angle forward and to the outside of the turn. The left front tire eventually bounced off the curb on my left. The bounce spun the car clockwise and pushed it towards the inside of the turn, and my right front tire came to rest against the curb on my right.

Nah, not the whole street. If you look at the map, that corner has a turn only lane. The lane has curbs on both sides. I slid across the lane. Since I was taking the turn at a *slightly* fast speed for the radius, I had tried to take it wide, which put me pretty close to the curb on the left to start out. I probably slid a couple of feet to the outside before bouncing, and then at most 6 feet to the inside, maybe less, I'd have to measure the width of the lane to be sure. And I was going over 30, not 25.

I suspect I was on wet pavement, perhaps some salt, and maybe some slush as I got close to the curb. I doubt there was ice involved, but I may be mistaken.

I've taken this exact same turn Monday through Friday in various cars for 2 years now. I know it well, and I thought I knew how fast I could take it in both wet and dry conditions. Like I said, I've taken it in my Prius at just over 35 MPH in the dry without so much as a whimper from the car. I slowed closer to 30 because I thought it was wet. However, I'm probably pushing the Prius around the turn a bit faster than I would have in my previous car. This is the first time it's been a problem, but I'll be taking all turns slower in the future, especially in wet or winter conditions. I really don't want to mess up my beautiful Prius.

 

Um . . . sorry, but your post is wrought with wrong.

1) "At best" the VSC will let you take corners faster than non-VSC without spinning out . . . but not to the point where you defy the laws of physics. If VSC didn't do this one basic thing, VSC would be useless. If you don't believe me, take another look at the youtube video I posted above. It is the VSC vehicle which made it through the turns every time and the non-VSC vehicle didn't. Therefor the VSC vehicle can and does allow faster turns, because the other vehicle couldn't negotiate the turns without spinning out.

2) I have yet to meet or hear of any "good driver" who has the ability to apply the brakes to individual tires. And there is no driver who can react as quickly as the VSC computer. And what happens when your "good driver" is behind the wheel of a VSC equipped car? Are they somehow a worse driver or less capable?

3) VSC has nothing to do with allowing you to hit the brakes to avoid objects . . . Anti-lock brakes do. VSC will help prevent the car from inadvertently going sideways, but if the conditions are that slippery, VSC isn't going to help you from hitting that object directly in front of you - you were toast to begin with.

 

Maybe I should temper my earlier 'useless in the snow' comments with a description of local conditions. Dry, fluffy snow on the flat would be easy in comparison. Snow here tends to be very wet, and turns to ice when compressed. Whatever amount melts during the day then freezes at night, making things very slick. If it's clear and cold, a thick layer of frost covers every surface. The sparkling diamonds are pretty to look at, but treacherous to drive on. No matter which direction I go when I head out the door, it's either up or down, and fairly steep. Given the choice of sliding into a parked car, under a train, or into the river, I think I'll walk. It'll all melt in a couple of days, anyway.

 

Thanks Sufferin'

You are restoring my faith in VSC. This is how I understood everything I had read about it in the first place, but since nobody was commenting here to confirm my beliefs, and drees seemed so certain of his opinion, I was begining to think maybe I had misunderstood something.

I agree that if it is possible to corner better without VSC, then VSC seems useless. I realize that I exceeded the limits of the turn in question, and I suspect that without VSC I probably wouldn't have made it as far into the turn as I did before hitting the curb. That probably would have been quite a bit messier. Instead, I was able to drive off with no damage, and no injuries.

 

You misunderstand, VSC definitely increases the stablity of the car by reducing the car's tendency to skid.

It will attempt to do that, but obviously if you are exceeding the traction available to all the wheels trying to corner, braking won't help much.

No, it will continue to try to point the car in the direction that you are trying to go. My wording was perhaps misleading.

There are two types of skids - understeering skids are the type where adding more steering input does not result in the car turning sharper, the front tires are losing traction. Adding more steering input results in the car going straighter as once a tire starts skidding, the more you increase the slip angle the more the coefficient of friction goes down (this varies depending on road surface).

Oversteering skids (such as the ones in the video Sufferin' Prius Envy posted) are the type where the car is turning sharper than steering angle indicates, the rear tires are losing traction, the opposite of understeer. Unless corrected, this results in a spin you pointing backwards.

To correct an understeering situation, you need to either slow down, or reduce your steering angle. Unfortunately, braking often does not help much as this tends to further overload the outside front tire. The most effective way to correct understeer is to slightly straighten the wheel and apply the brakes, hopefully enough to allow you to get the vehicle on the right path. A VSC system will reduce the throttle opening and apply the brakes on the inside of the car.

To correct an oversteering situation, you need to first correct the skid by reducing your steering angle and get the vehicle traveling in the same direction as the wheels. That is much easier said than done unless practiced, typically overcorrection occurs and you end up oversteering in the opposite direction. A VSC system will apply the brakes to the outside wheels before the oversteer gets severe enough that correction requires large steering inputs to correct.

The earlier video shows show the VSC system controls oversteer in common direction change situations. You'll notice that the VSC enabled cars all slowed compared to the non-VSC cars. I will also point out that the non-VSC cars appeared to have poor drivers who did not attempt at all to correct for oversteer situations (just look at the front wheel angle).

Understeer. The VSC did it's job, but unfortunately, you ran out of traction and room.

I said it above, but the drivers didn't appear to apply any corrective measures to avoid the spins they encountered. I wish I had 4 brake pedals that I could modulate, but I only have two feet.

Your typical VSC system steps in way too early for optimal performance (I'm primarily talking about dry roads here). The peak traction level of a tire requires some amount of slippage, but a VSC system will step in long before you get there.

Take a look at all the people complaining about the TC system stepping in too soon on slippery roads where some amount of slip is required to move the car. The concept is similar.

I'm sorry, but the VSC system includes the anti-lock braking system.

And damn, VSC doesn't make you invincible? I guess that explains the 12 car pileup on the freeway this morning.

 

Okay, good discussion here. I thought my understanding of it was a bit simplistic, so it's good to have an intelligent discourse.

That would be cool though if you could. Maybe a pedal for each foot that could detect heel and toe pressure. You have to incorporate a different method for acceleration then. Farm tractors for instance, have two brake pedals, one for each rear wheel, and an acceleration position stick behind the steering wheel. (Tractors tend to go for long periods at a fixed engine speed). I don't know if this is the same for 4WD tractors. I remember a combine that had a steering wheel for minor course corrections, and two hand sticks for braking either side to control the turns at the end of the field. I'm not sure about bobcats/skid-steer, but I think it's like a bulldozer setup where a lever for each side controls braking (pull back) and acceleration (push forward) for that side. And of course, airplanes have their own setup.

With the acceleration-by-wire and steer-by-wire systems that the Prius uses, it should be fairly easy to incorporate steering and acceleration (even normal braking) into a joystick and use both feet for more sensitive braking. Then for improved parallel parking, you could switch into a mode (second joystick?) where the back wheels could be steered independently of the front (there are some automated systems like this under test - at high speeds the back wheels steered the same way as the front, so you could change lanes while still pointing straight forward, and below a certain speed the behavior changed for really sharp turning).

But all of this would be too radical to survive in our marketplace, like the Tucker, with its 3rd headlight that was tied to the steering. <sigh>

 

Well it's confirmed ! (for Me)

6" of snow today, and the roads were not plowed. My wife came home from work to 6" of snow in the driveway, and it walked right up, with the stock tires. No problem on the mail route either ! She has to stop on occasion, up hill to do the mail drop, and had no problems going up hill from a dead stop.

It took me 5 runs at the driveway to get by S-10 (2WD) in the garage, and that's with a #200 tool box behind the rear wheels, and 6" of frozen ice and snow in the open box.

Do not worry about traction in bad weather, if you have VSC (traction control), pkg #2 Minimum. Snow tires would be that much better, but so far, we don't need them.

If you find a ditch, you would have found it with any other standard vehicle.

My .02

 

I consider the Prius to be a poor snow car due to its poorly implemented vehicle stability control. Mine is overly aggressive in cutting power to the drive wheels, doing so at the slightest hint of wheel slippage. This has the effect of shutting you down completely. It is nearly impossible to maintain momentum up a slippery hill as the VSC cuts power each time the wheels slip even a bit, and eventually it slows you to a stop. It's also a problem when pulling out quickly from a wet or snowy side street: if there's any wheel slippage at all, ALL power is cut off and you are left hanging (not much fun when traffic is racing towards you). I consider it to be downright dangerous and will not buy a prius or any other auto that does not allow this feature to be toggled off (as my lowly 94 Saturn did--why can't toyota manage this?).

 

Change "Vehicle Stability Control" to "Traction Control" and then add my emphatic agreement.

 

Actually, it's the standard-across-all-trims Trac that is killing the power, not the VSC. Although VSC appears to be standard on '08's, it was part of optional packages for previous years. VSC works to help minimise a skid if you should happen to slide

It's unclear from your post what year Prius you have. My '04 has the very aggressive Trac, and it can really disappoint me at times. My '07 FJ also has Trac, and it is far less aggressive and actually works with you

For example, if my FJ is in 2wd - as it is 99% of the time - and one rear wheel is on ice while the other rear wheel is on dry pavement, the brake will apply to the spinning tire and away you go.

No drama, no white knuckles, just go. I'm currently running Toyo Open Country G-02 Plus studless winter tires, am considering Cooper Discoverer M+S studded truck tires

I've always believed in running good winter tires - prefarably studded - in winter conditions. IMHO the Prius needs good winter tires more so than the average car, at least for the 2004 the Trac is far too sensitive. My Dad used to have a 2003 Buick LeSabre, and with studded tires it would easily blow the doors off my Prius running studded tires