Driving downhill on B (engine braking)

Someone please correct me if I'm wrong, but....

Using the B position allows mechanical engine drag to partially slow the car when descending a hill. This would reduce the energy available to charge batteries and create waste heat from engine friction. In addition, unless you are using LOTS of braking, energy absorbed from using the brake pedal to slow the car while descending is used to charge the battery and the friction brakes aren't used at all, at least until the batteries are fully charged.

So... the most efficient way to descend a hill in a Prius (unlike a conventional car) is to use the brakes until the batteries are full. This should also create the least wear and tear on the car. I don't think there is really any good reason to use "B".

 

Short and sweet: use "B" instead of riding the brakes on a long down slope (of course you can also use the brakes with "B" if "B" alone is not enough). Don't use "B" otherwise 'because it hurts MPGs.

 

I have only used the B position durring a long descent and worked fine, it does keep you from keeping your foot on the brake and that is nice The people in back of me stopped us to ask us how I maintained a slower speed without using brakes after we both ended up at the same place.
I told them it was the power of the Prius then told them about B and I put it in EV mode and then they were really impressed!!!

Coastal EV mod.

maybe sold another prius who knows

 

Paul,

In general a long enough down slope will be over 3 miles at 5% grade or greater.

I think of it mainly as a way of transferring waste heat from the brakes to the engine. So I really only use it if I think I'm starting to overheat my brakes.

After topping up the battery in D, I'll switch to B when coming down off Mt Rainier's NW corner, Hurricane Ridge, or some dirt road descents in the Cascade Mountains.

Other spots like the rest of Rainier, Mt St Helens, and the highway passes all have high enough speed limits that I'm never just riding the brakes in D. Also the higher wind speeds cool the brakes more anyway.

 

It's too bad there's no easy way to tell when you have transitioned from regenerative braking to friction brakes . That's part of the beauty of the design, it's pretty close to seamless. My understanding is that in the current generation you have to be close to a panic stop to transition away from regenerative braking, (or be under 7 mph). For normal hills (I live in the Boulder area and we have lots of them) I just use brakes to maintain speed. Even coming down high passes Loveland pass I rarely use B until I've fully maxed out battery charge.