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Question about B Mode

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Posted by G-Man on January 30, 2008, 1:31 pm
Using the B mode for long downhill grades is recommended.  Other than not
riding the brakes, does this gain you anything?  Does it generate more juice
for the battery like braking?  If not, it seems counter productive.


Posted by Mr Ed on January 30, 2008, 2:32 pm

It saves your Brake linings.  A free wheeling car can be dangerous on a long
steep down hill run with no engine back pressure.  I once owned a 1933 Chevy
with free wheeling.  Wow, was that scary with mechanical brakes and no

Mr Ed

Posted by Pete Granzeau on January 30, 2008, 7:09 pm

You can't tell when the brakes are actually in use in a Prius, since
regenerative braking is used as much as possible.  However, if
regenerative braking is insufficient for the amount of braking being
asked for, the mechanical brakes are engaged.  B mode does something
else: it gives the same effect that use of a lower gear in a standard
automatic gearbox does, by spinning the engine and using engine braking.
I live in an area where engine braking is virtually never needed, so I
have only engaged B mode a couple of times, just to see what it does.  I
don't know if it engages the brakes, too--but I think not.  It will
definitely reduce the demand for braking.

It's only needed for long, steep downhill runs--the kind where a traffic
sign "Use lower gear" probably appears.

Posted by Michelle Steiner on January 30, 2008, 7:18 pm

Friction brakes on the front wheels are generally used only under two

1. When the vehicle is traveling under six miles per hour.
2. In panic stops.

The rear wheels, though, have only friction brakes, and no regenerative

Support the troops:  Bring them home ASAP.

Posted by Pete Granzeau on January 31, 2008, 6:54 pm
 On Wed, 30 Jan 2008 12:18:50 -0700, Michelle Steiner

Yes, but are the rear brakes used when regenerative braking can handle
the load, or are they, too, used only when etc.?

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