From: andyh@chaos.cs.brandeis.edu (Andrew J. Huang)
Subject: Re: Using Brakes....a Clarification
Organization: Brandeis University
Date: Tue, 12 Jan 1993 17:37:33 GMT

In article <C0q0Ms.2I7@news.udel.edu> bew@brahms.udel.edu (Ben Williams) writes:
>Seriously though, in my mind it boils down to this:  Using brakes will wear
>out the brakes.  Using downshifting will contribute to wearing out the

To be fair, using the brakes will wear out the brakes and using the
clutch will wear out the clutch.  However, brakes will need
replacement three to six times in a 200Kmile lifetime while a clutch
can be reasonably nursed to last the entire 200Kmiles.  So putting
extra wear on brakes means an incremental bit of work while clutches
usually mean an entire new repair item.  Brakes are maintenance items,
clutches are repairs.

>clutch depending on how well you can match up the gear with your speed when
>you release the clutch pedal (I admit that I am far from perfect at doing
>this).  

You can achieve no wear downshifting only with extreme diligence and
practice.  The Right Way (tm) is to dump the clutch by sidestepping
the pedal on every shift to eliminate feathering and the associated
slippage.  If your right foot has done the Right Thing (tm) you won't
feel anything when you dump.  If your right foot hasn't done the Right
Thing (tm), you stress your drivetrain and sometimes visit the weeds
past the edge of the roads.

>(ah, there's the rub...) use and is, I assume, a bit more difficult to
>replace, I would think it was a better candidate to shoulder the task of
>slowing.  

Well, clutches, because they are difficult to replace, ARE designed
more robust.  However, are they robust enough to take both normal
usage as well as the additional load of downshift braking?  I don't
know and I'd rather not find out.

>Hmmm, now that I think about it, the clutch and the brakes are
>performing the exact same function, bringing two surface which are moving

There is a difference.  The brakes are meant to slip continuously and
repeatedly.  The clutch is meant to slip a little bit and then grab
tight without slipping for most of its use.  If a clutch slips for as
long as you brake, the flywheel will die.

>...That is, no frictional wear going on at all.

To take this to a ridiculous point, you could remove your clutch cable
and start off in gear, using the ignition key to come to a full stop.
But the point is that you can't avoid putting wear on these.  

Since there will be wear, you have to choose the activities which make
the wear worthwhile.  Downshift braking has no redeeming performance
value; you can stop better with the brakes alone.  It's one candidate
if you're trying to eliminate sources of wear on the clutch.

>But I don't remember my VW owner's manual saying I MUST NOT
>downshift.

But it also doesn't say not to drive into brick walls. :-)

>If I do, it's gonna be hard to break that habit I formed through
>years of doing it. 

I did it for years also.  If you think of pure braking as a new
driving technique, its easy to forget to downshift through the gears.
I still downshift to accelerate through corners.  But to come to a
stop or before I accelerate, I don't row through the gears.

I suspect that we haven't heard the end of this thread yet.  We may
have to take it for a vote.

Andy Huang


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