[Diy_efi] OT: ABS retrofit into older car...

[Adam Wade]

--- Mos <mos at sydney.net> wrote:

> I would've thought the front brakes are more prone
> to locking up first
> upon a heavy stomp, as they have more braking power
> to start with, and the
> front wheels are unloaded relative to when the car
> is actually slowing down rapidly.

Actually, that is exactly why the rears are more prone
to locking than the fronts.  With less loading, they
have a much lower friction coefficient with the
roadway.  That coefficient is not linear in proportion
to load; it is exponential.

However, it's far more important to maintain control
with the front wheels, since they steer the vehicle;
thus single-axle ABS is almost exclusively on the
front axle.

> What does properly biased mean? The correct bias (in
> reference to the
> force a tyre can hold) changes with deceleration
> magnitude, does it not?
> If you bias for maximal deceleration, then the
> fronts will be overbiased
> in slower deceleration, right? (And wont help you
> with stomping at all).

A much bigger issue (since cars have a fairly low CG
in reference to their wheelbase) is physical load
changes.  This is especially true in vehicles like
pickup trucks.

Volkswagen had an ingenious solution for their
Transporter in the 60s and 70s...  They had a
tiltmeter in the form of a ball-bearing check valve. 
the harder one hit the brakes, or the more the rear
lifted in a stop, the less it would bias the rear
brakes.  As long as the system had the fluid changed
yearly, it worked incredibly well.

=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=/   |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

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