Using the B gear in town, oversold Prius?

A Priori: That is a correct assumption, it was 2 different rides. Since that test with cool rotor temps with service brakes only, I have not gone back to "B" mode.

 

The US model has front disks, rear drums.

 

European models have disk brakes all around, but some come with steel wheels.

 

I don't know why this is so hard for everyone. Just like a regular Automatic car it makes sense to be in the D / OD selection 99.9 % of the time. Unless you are coming out of the mountains (like the Rockies) and you see the sign on the side of the road every 1/4 mile that says "use lower gear" you will never need to use "B". The reason this is important is because after driving several miles of straight downhill regardless of the vehicle you are driving your brake pads start to get really hot and are unable to cool quickly. Once they get to a certain point they start to become extremely ineffective at slowing you down hence the reason for a lower gear. Toyota probably could have labeled it with an "L" and could have saved some confusion.

 

There's an active volcano in my county. When I'm coming down from visiting the lodge at the Timberline (5,960 ft, 1,816 m), in D it's easy to get the battery solid green. When the battery has no more capacity to absorb regenerative charge, to protect the battery the Prius goes to friction braking, just like any conventional car. The brakes can get nice and hot when that happens. If I put the selector into B before I start the descent, it takes longer for the battery to go solid green and the friction brakes to kick in. I have more braking capacity in B since the car uses the ICE compression to waste the kinetic energy of descent. I'd rather have the car wasting energy compressing air and releasing it than turning it into heat in the brakes.

 

Thanks, that's what I thought. I didn't want to state that as fact without being certain, so I said what I knew for sure.

 

Anything that makes the ICE run is wearing it out. Engine wear is my main argument against using the B mode except when you would overheat your brakes on a very, very long downgrade.
Having been through mountains with two different Prioins (? plural Prius) I have rarely needed to use the B mode. The grade almost has to exceed 10% and more than two miles of downgrade to get above 70 MPH. So even in mountains I have not needed it.
I can imagine in areas with non-interstate type of road that it would be a very needed thing to have.
My two bits worth.

 

Engine wear? Probably not much of an issue in B mode, since it's just spinning, not firing. And the Prius ICE runs less than conventional ICE cars anyway, so you're still net-positive if you use B all the time (even though most people should probably never need to use it).

Accepted variants on Prius plural: Priora (for Latin scholars), Prii (for Priuschat nerds), Priuses (for those of us speaking the "common" tongue.)

Toyota should put Hobbit's B-mode article in the manual and make it required reading for their salespeople as well.

 

Not quite correct - in 'D' if you get the battery solid green and apply the brakes the ICE will spin faster to absorb energy just as in 'B" mode. Eventually the friction brakes will be used if the hill is long enough and steep enough.

Using B mode will delay filling the battery - so again it may be useful on a very long hill but the system automatically operates the same as B mode once the battery is full.

You end up with the unusual situation in this scenario that putting your foot on the accelerator pedal causes the engine speed to decrease!

kevin

 

Bill, are you sure the heat is from the brakes and not the volcano?

Tom

 

. . . and never while over 20mph ... or it WILL decrease mpg's.

 

When the HV battery is near the top of its safe charge level, regenerative braking simply stops. It feels much like the transition from regen to friction at low speed, there is no Eventually about it. I have experienced this many times.

The oddest thing is when you come to a stop with the full green battery and the ICE keeps cycling on and off quickly.

 

It freaks people out when that happens: "Why does my engine keep starting and stopping? Is this normal?"

Instead of using the ICE to burn off excess charge, I wish Toyota had equipped the Prius with a big bubble lamp, like the ones on Christmas trees, only a lot bigger. It could stick up through a hole in the hood, so you could see it light up and bubble at the bottom of big hills.

Tom

 

Yes but then it automatically goes into engine braking as in B mode - the friction brakes do not come on unless you apply much more braking pedal pressure.

kevin