As with drinks, and one or two other things i'm sure, the stiffer the
better.
;-)
Joe
___________________________
Dr. Joseph Garner
University of California
Department of Animal Science
One Shields Avenue
Davis
CA 95616
USA
Phone: (530) 754 5291
> -----Original Message-----
> From: Max Heim [mailto:mvheim@studiolimage.com]
> Sent: Tuesday, August 01, 2000 10:41 AM
> To: mg's
> Subject: Re: Stiff Brakes
>
>
> Interesting. He may be overstating the case for rhetorical
> effect, but
> basically that is how I feel about brake pedals, too.
>
> Look at it this way: there are two feedback mechanisms available for
> modulating braking effort. Both of them are feeding back
> through the sole
> of your foot and your leg joints, not the most precisely
> sensitive parts
> of the anatomy (few of us can type with our toes, for example). One
> mechanism is spatial positioning -- i.e. the distance the
> brake pedal is
> depressed. Those familiar with large American cars with power
> brakes are
> aware of the shortcomings of this approach -- it is very difficult to
> tell precisely how far one is moving the pedal with one's foot in the
> absence of resistance. One certainly can't be accurate within the
> quarter-inch or so that is required, unless one depresses the
> pedal very
> carefully. Of course, in an emergency, one tends to want to apply the
> brakes quickly, resulting in instant lock-up. Adding to this is the
> factor of one's weight transferring forward during heavy braking,
> sometimes leading to lock-up even when one had modulated the pedal
> properly to begin with.
>
> The other mechanism is resistance. It is much easier to precisely
> modulate the amount of force one is applying with one's leg,
> compared to
> the amount of distance of foot travel. This is easily demonstrated by
> attempting to push some small object with your toe a precise distance
> across a smooth floor without looking -- it is difficult to get
> repeatable results. Then try placing one foot on the bathroom
> scale and
> applying a specific "weight" -- look away from the scale and
> try to match
> it without looking. Much easier, no? That's because you have tactile
> feedback. Then think about the emergency stop situation --
> your initial
> brake application can be as quick as necessary, but the instantaneous
> feedback you get from the pedal resistance allows you to modulate it
> short of lock-up.
>
> I think as a practical matter of brake pedal design that there will
> always be some pedal movement, but I feel it is very
> important that this
> be exactly proportional to pedal resistance, in order to
> provide useful
> and accurate feedback. I don't think the importance of
> tactile feedback
> can be overstated in this case, yet surprisingly many manufacturers
> persist in producing "dead", limp, soggy brakes, presumably
> as a result
> of customer preference. But then, human factors is still a neglected
> aspect of design, after all these years... I mean, look at
> Windows <g>.
>
> Eric had this to say:
>
> >Searching the 'Net to help out a friend of mine with BMW
> break problems
> >(and who seems incapable of using a search engine - but that
> is another
> >story) and I bump into the following statement.
> >
> >"The one thing about brake pedals is that they can never
> really be too
> >stiff. Anything that can be done to reduce brake pedal
> travel is going
> >to improve sensitivity and confidence under heavy braking. Ideally
> >pushing on the brake pedal should be like pushing your foot against a
> >brick wall. The pedal would not move at all and you would
> modulate the
> >brakes strictly by changing the force with which you pushed
> against the
> >pedal. This is pretty much what a top level racecar brake pedal feels
> >like (F1, CART ,WRC etc). Brake pedal travel and effort are
> adjusted by
> >changing the amount of fluid moved by the brake pedal. This can be
> >accomplished by changing the leverage ratio that the brake
> pedal has on
> >the master cylinder or it can be achieved by changing the diameter of
> >the brake master cylinder. The latter method is most common."
> >
> >Now personally I prefer a little bit of 'sponginess' at the
> top to give
> >me more 'feel' of the brakes... but I do want to find (and
> know where)
> >that rock hard, this-is-as-fast-as-you-can-stop, level is. I would
> >worry if I had no downward play in my brake pedal.
> >
> >Any comments? Is this just personal preference on my part - or
> >silliness.
> >
> >
> >Eric
> >'68MGB MkII
> >
> >PS For Sprinting, I have large MetalKing brake pads that certainly do
> >stop the car :-)
> >
>
>
> --
>
> Max Heim
> '66 MGB GHN3L76149
> If you're near Mountain View, CA,
> it's the red one with the silver bootlid.
>
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