Braking downhill on an icy road

I would select B mode for engine braking.

 

Putting the car in Neural invokes full-automatic "just take me
to the office" mode, where the DRCC and parking sensors and
front and rear cameras are used as a whole-environment sensor
array in conjunction with the tractor beams to generate force
against the cars ahead, nearby buildings and trees, etc to slow
the car down regardless of the frictional coefficient underneath.
It's the final answer in making drivers truly invulnerable. But
remind me where that button is located, again?
.
_H*

 

A non-hybrid vehicle on ice tries to brake against the idle speed of the engine. Mail carriers learn to shift to neutral as they approach a mailbox (uphill or downhill) to stop the push from the transmission. Try stopping 400 times a day at mailboxes on ice, that stretches your nerves to their limit.

Shifting to 'B' usually isn't necessary. When you let off the gas pedal the Prius starts regenerative braking, a gentle slowing of the car, similar to shifting to neutral. 'B' mode may cause too much braking and loss of control. Applying the brakes increases the regenerative braking without using the engine to slow down.

Try each method in a parking lot to get familiar with how a Prius reacts, it is different than a normal car. Jerry

 

Just press on the brake pedal. The Prius computers will do all of the tough stuff for you.

Tom

 

My thoughts:
For braking on ice one usually wants to maintain steering control (front wheels keep rotating, and are not locked up and skidding).

Braking with just the rear wheels (parking brake) is often better than braking with just the front wheels (down-shifting a front-wheel drive car).

If gentle, effective braking on all 4 wheels can be achieved, that would be good.

Skidding on all 4 wheels is generally not good.
Perhaps, best to slow down earlier and drive with chains or other high-traction tires?

 

Everything you mentioned is taken care of by the ABS system. If you need to stop on ice just push the brake pedal firmly and don't let up. While braking with ABS you can continue to steer around obstacles while the system gradually slows you to a stop.

 

Yours has a neural mode?! Wow, mine doesn't even have USB.

 

Does the ABS continue to function if all 4 wheels are locked?
The speed sensors would tell the ABS that the car is stopped.

 

ABS will not allow the wheels to lock. It applies and releases the brake on each wheel independently to keep them from locking.

 

Abs is an excellent driver aid but it does struggle in ice and especially snow. Many scandanavian cars still have a manual disconnect for abs as on snow you want the wheels to lock as this creates a mound of snow infront of the wheels slowing the car down very well whereas abs keeps the wheels turning and the car skips on the snow rather than digging in.

Many cars now have ebd brake force distribution also known as 'ice mode' on some abs systems. This kicks in when the car senses the rears locking up before the fronts (this is always bad as it wrecks directional stability). This usually is a valve that shuts off braking force to the rears and doesn't allow rear braking until reset by lifting off the brake completely. This is done as even abs can't always react quick enough to rear wheel lock up and you can still spin an abs car under braking. This can make the brake pedal feel odd - one of my cars it feels like the brakes have failed as the pedal goes rock solid.
All I'm saying is abs isn't a magic get out of jail free card in all cases and it works best when you work with the system rather than planting your right foot heavily on the pedal.

I've found even with and equiped cars that you can gain more traction by using left foot braking with a little throttle. In this case it's much easier to control the braking force and doesn't make it so sensitive. Of course be careful not overheat the brakes

 

... except under extremely slick, glare ice conditions, if every wheel starts sliding simultaneously. The one time my Subaru did it, I took it as a sign from above that this particular trip was not to be, and very slowly turned around and crept the two blocks back home. Nobody made it to that Christmas party. Hundreds of cars were abandoned overnight along local streets and highways.

I have no winter experience with the more modern Prius system yet.

 

Well to be fair ABS was never designed to shorten stopping distances. It was designed to allow you to maintain steering control during hard braking.

As far as locking the front wheels to allow snow to build up in front of the tire, that really only works in soft snow that hasn't been packed down by traffic. I've never really had trouble stopping in soft snow. On hard packed snow very little is pushed up in front of the tires and preventing wheel lock is your best chance of stopping safely.

ABS only works if you apply and keep applying the brake. If you pump the brake like we were taught in the old days you might as well buy a car without it.

 

ABS is NOT designed to stop you quicker than a non-ABS car. My FJ has two pages of warnings to this, in effect, cautioning that braking on snow and ice will be LONGER

Also, since most drivers in Scandinavian countries will run studded tires in winter, on glare ice you will stop much quicker if the studs can bite in. Though driving on glare ice roads this Saturday



I had no trouble whatsoever with the factory studded Nokians. If you're on glare ice, only a studded tire will provide traction

 

Of course the best advice is to avoid driving in these conditons but sometimes we have to. I drive big rigs for a living, and I'm not comparing the way it handles to a Prius but the laws of physics apply to all moving objects regardless of size and mass. We are taught never to freewheel your vehicle in neutral when driving in icy conditions. Even with all the the high tech these cars have it still boils down to your control of the vehicle because once you lose control of your vehicle in icy conditions nothing will save you except for your luck and faith. Slow down to a speed your driving skills will allow and anticipate vehicle movements ahead and behind you the best that you can at all times.

 

This advice doesn't apply to the Prius, where the drive by wire system will ignore the conflicting inputs and simply brake. Likewise most of the braking is regenerative, so it is not likely that the brakes will ever overheat.

Tom

 

I asked this in another thread... if driving in snow/icy conditions, when the system detects the rear-end sliding, will the system try to brake the rear wheels to slow the car down?

I am asking because the rear-end swapped on me when I was driving another brand's FWD and it scared the !#$*!% out of me.

 

ABS comes into play when any of the wheels slip during braking. ABS brakes all four wheels.

VSC controls power and brakes individual wheels to keep a car from skidding. Both VSC and ABS will help keep a car from spinning out as you describe. Likewise a good driver will do the same. It has little to do with front wheel drive, and everything to do with good driving technique. That said, the Prius is pretty good at saving bad drivers from themselves.

Tom

 

I dont know what to say = /
One thing I could tell you is that the car can figure it out all on its own.
I see my VSC (Vehicle Stability Control) light on all the time if I am in snow, or ice.