Re: Downshifting for Normal Driving

[elliott@yrl.co.uk]

jonb@u.washington.edu wrote:

>I disagree that today double de-clutching is useless. I do alot of
>mountain driving over the Cascades in Washington state and a lot of
>snow/ice driving going over there in the winter. How, I ask rhetorically,
>do you down shift at speed to either have engine braking on long down
>mountain stretches or to slow under control in marginal friction
>conditions?  Seems to me I don't want to simply put the clutch in, let the
>syncros do their business, and then let it out forcing the clutch surfaces
>to even out transmission revs with engine revs. Am I missing something
>here?
>
>	- jon
which was in reply to  escoses@earthlink.net 
><snip double declutch definition>
>> 
>> Good drivers used to be able to shift gears without using the clutch at
>> all. they did it by having a good ear for the right RPM at which
>> everything was balanced.
>> 
>> Double de-clutching (or double clutching) today is a waste of gasoline.
>> But if you have a high Db exhaust sounds good......but useless!

These are both good examples of an interesting debate that seem set to run for ever.

Like the best debates, you can choose which bit you want to
defend.

I offer :-) the following sort-of c  program to sort out the logic

    if (engine braking is desirable)
        if (matching engine and transmission speed is desirable)
            if (using brake at same time)
                if (double declutching is desirable){
                    be_smug_about_it();
                    double_declutch();}
                else
                    enjoy_yourself_either_way();
                heel_and_toe();
            else
                engine_brake_on_long_hills();
                //you know your limitations
        else
            sell_your_ur-q_to_someone_who_appreciates_it();
    else
        if (being in the right gear is cool)
            heel_and_toe();

Here are some notes to accompany the program

Is engine braking desirable?

    A 1000 Kg car braking at the limit of
    adhesion is dissipating 150KW. Brakes
    get VERY hot if done for a long time or
    very often (cf TV of night-time
    rallying) Us lucky ur-q owners have
    cars with 150KW engines. They are
    designed to deal with at 150KW.
    Therefore using them for braking at
    lesser rates than on the limit of tyre
    adhesion is not going to hurt them
    much. Not only that, you are wearing
    the other side of the bores, and the
    other side of gear teeth under braking.
    Engine braking makes for even wear!:-)

    If you have heel and toed, throttle blipped
    and whatever to match the new engine speed to
    the lower gear, there is no sliding between
    the clutch faces, so all this malarkey about
    wearing your clutch out only applies to mug drivers.
    (You eventually have to get in the right gear,
    so you operate the clutch just as  often, just
    earlier)

    Under engine braking, your brake pads are as free
    as the air. They ARE the air. Instead of brake
    disks working against brake pads, the energy is
    dissipated by the friction of air getting sucked
    through the engine while the throttle is closed.

    Therefore engine brake down long hills at least.

Is being in the right gear as you come out important?

    Are you a driver or do you just aim it?

    Heel and toe as you go into the corner, don't
    worry about whether the engine is braking or not.
    It's sheer pleasure having all the gear changing over
    during your turn-in, you can then sit back
    and enjoy the cornering.
    Dammit Jim, that's what these cars are for!

Double de-clutching useless?

    Nearly. You could argue that a double
    de-clutch spins up the front of the
    gearbox more elegantly than scraping
    the synchros at the (lower) cost of
    clutch hydraulics and throw-out bearing
    wear. Both are nearly indestructible,
    so what the hell. I always
    double-declutch downshift using both
    sides of my foot style heel and toe,
    but it is really done for fun and that
    being brought up on the biggest heap of
    useless brake and gearbox junkheaps
    (otherwise known as old British cars)
    has taught me ONE good habit.

How to tell a heel-and-toe driver.
His/her brake lights go out just after (s)he starts off uphill.