Date:         Wed, 22 Jul 2009 06:38:16 -0500
Reply-To:     Larry Alofs <lalofs@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Larry Alofs <lalofs@GMAIL.COM>
Subject:      Re: Friction
Comments: To: John Rodgers <inua@charter.net>
In-Reply-To:  <4A668DBA.1000404@charter.net>
Content-Type: text/plain; charset=ISO-8859-1

Interesting question, more complex than I thought at first.
  With the trans in neutral, depending on the design of the MT, there
is still some frictional coupling between the input end and the out
put end, depending also on the viscosity of the lube.  In most MTs I
believe this would tend to make the two ends turn at the same speed as
if it were in high gear (straight thru).
   Assuming that the clutch pedal is not depressed, the viscous
coupling in the trans could then either help or hinder the coasting of
the vehicle depending on its speed and the rpms of the engine.  If the
vehicle is moving fast and the engine is idling this effect would slow
the vehicle slightly.
   If the clutch is depressed, the engine speed is not important.
There will still be some frictional drag as the output end of the
trans turns or tries to turn the input end.  The frictional energy
loss at the throwout bearing is not relevant because it is just the
engine vs. the clutch fork.
   Now of course if the clutch doesn't release completely.....ugh, too
complicated for this early in the morning.


Larry A.


On Tue, Jul 21, 2009 at 10:55 PM, John Rodgers<inua@charter.net> wrote:
> This came up today.
>
> if one were to coast, and allow momentum to do the pushing - which
> scenario would have the greatest resistance against rolling.
> 1) Coasting with manual tranny in neutral. clutch released
>
> or,
>
> 2) Coasting with Manual tranny in neutral, clutch pedal depressed.
>
> Curious minds, and all that........
>
> Thanks,
>
> John Rodgers
> 88 GL Driver and proud owner of new Altimax RT's 205/70/R14 XL 98T  (grin!)
>