Subject: Re: How to Smoothly Downshift a Manual?

From: [email-masked] (Yasuhiro Endo)
Date: 18 Oct 1995 19:34:04 GMT

In article <[email-masked]>,
>[email-masked] (Name withheld by request) wrote:
>
>
>>     What is the best way to smoothly downshift a car with a manual 
>>transmission, that would cause the least wear and tear?  Various sources
>>have provided different methods, such as releasing the clutch very slowly,
>>double de-clutching, and increasing the RPMs right before a downshift. 
>>Which method would be best for the transmission/clutch/engine?  Any
>>response in this matter would be greatly appreciated.

My first advice is to get some idea on how the drivetrain works.  Once
you learn what you are dealing with, you can analyze the problem and 
find answers yourself, which could be a lot more useful than answers 
that you might get here.  Driving is not a simple task (as with many 
the problems, if you think it's simple you aren't really understanding 
the problem), and there's a limit to how much idea I can convey in 
a short reply...

You should release the clutch slowly only if you are a wuss.  This is 
not very good for the clutch, and more importantly, you will lose the 
option of controling your car via the gas pedal while your clutch is
completely disengaged.

Double de-clutching is not necessary unless you have a worn-out gearbox.
Double de-clutching can be useful in some occasions, but you ought to 
learn how to match the rpm of the engine first.

Richard Moburg <[email-masked]> wrote:
>
>Get a sense of the RPM difference in each gear, it is usually around
>750 to 1000 rpm. Try to bring the RPM up in anticpation.
>In other words if you were turning 2000 in 5th bring your RPMs up to
>around 3000 as you engage the clutch in 4th. I t doesn't need to be
>rushed and you will smooth out in practice.
>By the way this is the same method (with a little heel and toe
>breaking) that is used for racing.
>Different cars have different RPM variances between gears so make a
>sudy of it as you shift up and down.
>

A good way to practice this is to bring your car to about 30mph and 
go through all the gears between 2nd and 5th (and release the clutch 
with each shift, obviously) while maintaining the same speed.  You can 
even include the 1st gear in this exercise once you get good at it.

In order to avoid the "jolts" that you might get when you release the 
clutch, you have to match the rpm of the engine with the rpm of the 
transmission imput shaft.  The rpm of the input shaft is determined 
by the speed of the car and the gear that you are in as the previous 
poster noted.  You have to "blip" the gas pedal to bring the engine 
rpm up when you downshift, and you have to wait (however short this 
wait may be) for engine rpm to drop when you upshift.  For example, 
if you are going from 5th to 4th, the sequence will be:

	1.	clutch in
	2.	gear to the 4th (since the car's speed hasn't changed much,
		rpm of the input shaft will go up)
	3.	tap the gas pedal to bring up engine rpm
	4.	clutch out

	Note that step 2 and 3 can be overlapped, and once you get good
	at this, the entire process can happen very quickly (maybe less 
	than a second).

Be sure to practice when no car's around.  E-mail me if you want more info.

y.e.
-- 
Yasuhiro Endo				e-mail:	[email-masked]
Graduate Student - Computer Science	mail:   Aiken Computation Lab G24
Division of Applied Science			33 Oxford ST.
Harvard University				Cambridge, MA 02138
http://das-www.harvard.edu/users/students/Yasuhiro_Endo/Yasuhiro_Endo.html