B again

I never use B in winter. If you use it to slow you are only braking on 2 wheels. And the abs can't protect you from skids.

 

Think of B as pre-applying your brakes, or a brake offset if you will. Except the brake offset is accomplished by regen and ICE.

I suppose B braking could be reduced by pressing the accelerator pedal. But then you have 2 pedals to deal with, instead of 1 to slow down.

 

I should re-read the manual. I was unaware that ABS was disabled in B mode. Doesn't make a whole lot of sense to me because B mode is a low gear "simulator", and I'm not aware of any vehicle with an automatic which disables ABS when you shift into a lower gear. Seems counter intuitive and unsafe considering that a driver may use B and hit the brakes at the same time to come to a stop, in a panic situation. Well, I will go to the manual when time allows and I will try to report back.

My climate does get snow, sometimes a lot, sometimes a little. I learned to drive in the snow without ABS on a vehicle, so I have to remember two different slick road braking techniques. The old technique of pumping the brakes to prevent locking, but also adding into that shifting the vehicle into a lower gear (like B mode on Prius) gives you more control when going down a suspect hill that might be slick. Something I will not do is shift to neutral on the Prius when trying to come to a stop. That works in an automatic because it disengages the natural forward pull of the drive train. Thus amplifying the sensitivity of the braking system because it does not have to fight against the natural forward creep of a standard automatic.

The other winter braking mode is of course ABS braking where you stand on the pedal and hope for the best. Since the Prius has ABS I wouldn't be afraid to do that either. However, I would hope that B mode would be available because that would actually enhance a short stop rather than hinder it. Many years ago I had to use my parent's Explorer to get to work on a bad winter afternoon. Coming down a hill while braking I found a slick spot and ABS kicked in. When I felt that pedal going I just pushed harder and put the vehicle in 2 and I came to a rather quick stop. ABS continued to work in 2. I know for a fact that particular implementation of ABS on that vehicle would not operate in 4WD, however.

I would not put the Prius in N for braking. At that point you are solely relying on the hydraulic braking system for all braking effort. The regenerative system is very controlled and smooth and as such I'm inclined to believe that it offers superior braking control, at least until a lockup, but I have yet to have a lockup with this car.

Anyway, the Prius brakes most of the time with 2 wheels. Since regen braking is such a major component of the brake system on this vehicle, and since Toyota designed to squeeze as much energy out of the regen system, most braking sequences are entirely regenerative until you reach 7mph and the hydros take over. Regen is only on the front wheels so essentially you are braking with only 2 wheels all the time. When hydros kick in under the threshold then the rear brakes would be available to operate.

Anyway, with most vehicles, anywhere from 60% to 80% of all braking is done with the front wheels rather than the rear wheels.

 

Hi Maggie. I also live in Mass and have to commute along Rt. 2 East to 495 North. Lots of hills and turns along my way. As I was reading down this tread, I was thinking two things: (1) exactly what Dr. Fusco indicated -- I'd rather have control of when I start/stop braking and/or accelerate and (2) (especially after the past week or so) I'll need and appreciate having the extra battery power for stop-and-go action.

I don't know if this is a good thing... just what I feel comfortable doing myself. Of course... this is my first winter w/ my Prius... much more to learn I'm sure.

 

My deepest sympathies.

 

If pad contact with the brake rotor occurs only below 7 mph the rotor should not heat up. Has someone tried touching the rotor after a drive? Or spraying water on it so see it generates vapor? While breaking lightly down some hills I can hear the pads making contact with the rotors, I don't think that pad-rotor contact is all that rare in this car.

 

I use N B D what ever gives me the best control. I've even put the Prius in R on ice with no ill affects. Hit the brakes, watch the speedo when it goes to 0 put car in R and slowly release the brakes. Try it on glare Ice sometime. The more you know about your car the better. On glare ice I much prefer N and light braking at least you have steering control with the slightest release of brake pressure, some thing a lot of times you loose in D. What ever it takes to stop on ice. If it's that bad you really should have studded tires, or chains. 12 winters in northern Canada. In D or B your really only slowing the front wheels, not ideal for maintaining control and with most front screws your better off giving it a slight amount of gas in a skid to pull the car straight. Most 4x4's dissable the ABS in 4x4 Hi or low as it just loads the transfer case which is applying brake force to both ends by direct mechanical connection. The only thing that the Prius needs is a hand operated emergency brake to allow you to help straighten out a slow speed skid, if both brakes are properly adjusted. Don't put your finger on the rotor use a infared thermometer.

 

OK, and this may be a silly question, then why did Toyota put this "B" in the Prius?

What's it really for?

Thanks,

Aaron

 

I think that it's primarily for really long, steep downhill sections where you don't necessary want to have to ride the brakes the whole way down. As I recall some folks posted info to the fact that B doesn't charge the battery as efficiently as light/moderate braking in D (some thing about 30 amps vs 60 amps). Can someone confirm that? Anyways, it seems pretty useless most of the time but is probably pretty useful in certain situations. I've yet to use it.

 

That makes sense, thanks tripp!

Aaron

 

Yes, I have touched the rotors after my normal commute and found them cold. Pad-rotor contact is not rare, it happens every time I come to a complete stop. It is rare under normal driving conditions. I believe 100,000 mile pad life is possible. I have 30,000 on mine and the front pads show less than 10% wear.

I'm not sure what you hear when braking lightly down some hills but I doubt that it is pad-rotor contact.