Driving on packed snow long distance

bobjeri,

made that run a number of times in the 70's in the snow in a VW
Squareback Variant.

Seems like I was always driving at night when it was only me and
the 18-wheelers on the road -- and they drove like demons, far
faster than I felt was safe. So they all passed me. And if it was
slushy, they threw massive waves of slush on the car and the
windows. I had to come nearly to a stop for the wipers to have time
to clear the windshield. I was often terrified, especially if there was
another truck coming up behind.

I learned to stop at a motel as soon as I didn't like what I was
seeing --that is, when I could see.

If it was absolutely, insanely necessary to keep moving, I'd pull off
at an exit and wait for a snow plow to come by and fall in behind.
Yeah, you know it, they too drove at maniacial speeds.

Good luck, and God bless. Be careful out there...

 

With those tires it will be as good or better than any front wheel drive. Keep in mind that the Prius sits fairly low to the ground, so you can't plow through deep drifts.

Tom

 

The main thing is to shift into "B" which gives you the gas pedel control of the drive wheels instead of freewheeling. This is will give you a simular feel for traction that a conventional transmission would give you though gas milage will suffer.

 

B mode won't really help with traction: you still have the same tires gripping the road and they will still be used in exactly the same way. What B mode will do is let you keep your foot on the accelerator pedal when going down a long hill. Otherwise you need to shift back and forth between the accelerator pedal and the brake pedal. That works fine, but B mode does inspire a sense of more control, even though it is an illusion. I have used it more than once for just this reason, even on dry pavement.

Tom

 

I would not recommend the use of B mode at all, unless you're coasting down a very long, steep grade.

It would be a good idea to ensure the washer fluid reservoir is topped up.

 

I'd rather brake than use B mode, braking allows the ABS to work, a slide in B mode is uncontrolled except by the driver. ABS works quicker than you can react. Stability control will help. B mode will give the throttle a more "on or off" feel. Gentle inputs is what you want on slippery stuff.
Live a little, don't fly.

You only live life to the full when you feel like life is on the line.
Stop frequently, have a coffee with a local.
Ever wondered why boredom is in epidemic now days?

 

ABS and VSC can't control the B mode.

 

Thanks for the info about ABS in the B mode. I was raised in Colorado and am a very experienced snow driver. I trust my own skill more than a machine thinking for me. (That's why I have not upgraded to Windows Vista ... but that is another topic. )

However, ABS is a good thing and I did not know it was disabled in the B mode. (Why would they do that?!?) Where the rubber meets the road is the most important part of this equation and as already noted, the tires are more than adequate.

As always, an interesting topic.

 

Hang on, you haven't understood what I am saying.
ABS is not disabled in B mode!
When in B mode the HSD uses energy from the wheels to drive the engine thus retarding the forward motion of the vehicle. The ABS has no control over this retardation. Should the front wheel start to slide while in B mode with no foot on the brake it will continue to slide. This is in a very low grip situation I am talking about. If instead you use light pedal pressure on the brakes while the car is still in drive the computer will look after retarding the forward motion of the car. The ABS will almost instantly, faster than you can react, switch from electric regeneration braking to hydraulic friction braking and will apportion the brake force to the wheels with the most grip, you can not do this manually. This is why I say it is better to use gentle braking than B mode.

VSC works all the time but VSC is not ABS, it will bring the car straight or assist with cornering but it wont stop a straight line skid, that is the job of ABS.

Have we all got that? B mode does not disable ABS, ABS has no control over the HSD functions except regenerative braking which it can only turn off to switch to friction brakes.

 

B mode seems very complicated, but the basic concept is this: it produces more braking force when you lift off the throttle than the car does in D mode.

The exact approach it takes depends on the charge of the battery and the charging rate. It will use engine braking a little more aggressively than D mode to reduce the amount of charge generated, to prevent overcharging the battery.

Generally when snow driving in a regular car, you want to be in the highest gear possible to prevent the wheels locking up under the influence of engine braking. Therefore, stay out of B mode which simulates a lower gear.

 

Yeah, what he said.
Thanks Mike.

 

Ah Ha! Thanks so much for correcting my misunderstanding. I drove a 1996 Camry for many years before buying our Prius 3 months ago. The Camry normally has overdrive "on" that saves gas by letting the engine drop back to idle whenever you let up off the throttle. Essentially "freewheeling." This is not good in snow and ice as you want a direct link between the throttle and the drive wheels for maximum control. Therfore, I would turn off the OD on the Camry in snow conditions.

I assumed that this was the same case for the B mode on the Prius as it feels similar in the throttle pedal.

After reading more about the PSD (Power Split Device) I now better understand what a different bit of engineering is in the Prius. (Damn elegant is what it is!)

So thank you Patsparks for correcting my assumptions. I agree that light braking is the way to go since the various systems in the Prius will provide the best control. (ABS, PSD and VSC)

 

If we are assuming driving on very slippery or icy or very slush filled roads then BRAKE mode will give the most firm and absolute control, especially when driving down a steep mountain slope. Of course Brake is selected early and not when driving overfast. All the other hypothetical technicalities may apply, ABS, VSC, when driving fast on a dry road. but that was not the question. Whether one is driving a Camry, a manual shift or a Prius: maximum gear control in snow is the goal with no sudden moves. Light braking in a overfast situation leads to heavier braking which leads to a out of control skid. I'm sure all Pat's comments were technically correct, but we are discussing driving in hairy conditions, which always means slow. I also had a Camry (84) and drove exactly as you did. The OP's initial instincts and past experience is/was correct!

 

As further clarification, when using B mode or just plain regenerative braking, all braking is done with only the front wheels. If either wheel looses traction, the control system disables regenerative braking and switches to friction braking, where full ABS is in play on all four wheels. This transition works very well, but often scares the bejesus out of drivers not familiar with it. The momentary reduction in braking feels as if the car is accelerating and shooting forward. Obviously it isn't, but our human brains interpret the reduction of deceleration as forward acceleration. Don't let if fool you into panic. Just keep pressing the brake pedal and everything will work just as it should with ABS.

Tom