[A4] A4 clutchless shifting
tyson at up-times.com
Fri Apr 20 14:20:45 EDT 2007
I would be curious to see the numbers of your fuel mileage when turning your
car on/off at lights. Fact is, unless you got some mondo long lights, I
would bet that you come out losing money. Reason being, the startup fuel map
on just about any car is SO RICH that you would be better off idling for 5
minutes than cranking for 2 seconds. I don't think that the difference in
fuel is that huge, but you also got to think about the extra residuals that
you a coating your exhaust system with from a very rich combustion.
As far as downshifting, it is a very good thing to get in the habit of.
First of all, unless you are very aggressive about it, it does not hurt the
clutch. The friction in a downshift is actually in the opposite direction of
regular use and makes the little fibers on the clutch stand up more making
it more gripy and less susceptible to glazing. It will contribute a little
more the wear of the disk itself, but Audi clutches are well designed and
can handle it.
The most important benefit is in handling. Hitting the brakes (even with
ABS) on a slick corner can make the wheel lock and slide sideways.
Downshifting on a turn keeps the drive train moving and even if you do lose
grip, the wheel will not lock. By rotating it will not get stuck in one
place, overheat and lose all traction in a split second - it will be much
more predictable and gripy. It will also contribute (with proper steering)
to pull you out of the spin.
Also, it is good for your engine to downshift. When downshifting your engine
works as an air pump - no real ignition going on there and cools off very
rapidly. If you have an EGT gauge, you can observe this very easily. Guys on
the track compression break not because their brakes are insufficient, but
because they want to keep their combustion temperatures low - especially
important on a highly tuned turbo cars.
Perhaps I am not the best at explaining these concepts, but I have been
racing Rally and Autocross for quite some time and even help teach autocross
schools at the local tracks - this is all much easier to demonstrate on the
track. That being said, you should never rely on the thin edge given to you
by downshifting on the street. There are too many variables there and you
should always take it slow. However, the skills learned, like proper
downshifting, will help you on the street handle your car better.
Technical Manager, Uptime Technical Solutions LLC.
tyson at up-times.com
From: a4-bounces at audifans.com [mailto:a4-bounces at audifans.com] On Behalf Of
Sent: Friday, April 20, 2007 10:16 AM
To: Robert King
Cc: a4 at audifans.com
Subject: Re: [A4] A4 clutchless shifting
IMO, one of the major causes of clutch wear is 'riding' the clutch. This
has been mentioned in the discussion, but, again IMO, should be
emphasized. I have driven with many people who consistently drive with
their left foot resting on the clutch pedal, as if they are afraid they
won't be able to find it if their foot moves away from the pedal. ;-)
Even worse, many of them get 'upset' when I mention that to them.
Similarly, using the clutch, instead of the handbrake, to hold the car
stationary while on an uphill incline will cause increased clutch wear.
Clutches are meant to be binary: ON or OFF. Unfortunately, the act of
starting from a stop has to involve some clutch slippage, so the sooner
you can match engine and road speed the better. Read: for minimum clutch
wear use relatively low engine speeds until the car gets rolling & the
clutch becomes fully engaged.
FWIW, I always sit at a stop light with the transmission in neutral &
the clutch engaged (foot completely off the clutch pedal). Actually,
with the recent high fuel prices, I will turn the engine off if I just
'miss' the light & know that it's a longish stop. Hmmmm... how many
starts to a starter? ;-)
Nanoose Bay, BC
2002 Audi A4 3.0 - Silver
1998.5 Audi A4 2.8 - Silver
1985 Mazda Rx7 GSL-SE - Black
email: stephen at kormilo.ca
Robert King wrote:
> On 4/20/07, Tyson Varosyan <tyson at up-times.com> wrote:
>> By sitting at a light with your foot holding the clutch pedal you are
>> serious damage to the clutch system.
> Sorry, but I've GOT to disagree with pretty much everything you posted.
> you like, I can get an authoritative quote from a good friend of mine who
> designed drivetrains for Ford, but for now I'll just say:
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