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

[Scott F. Williams]

Mos. 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.

Shocking the tire contact patches by stomping on the brake pedal extremely
abruptly makes it possible to lock up the front tires first -easily so in
slippery conditions. However, under most circumstances the rear tires are
the unloaded ones during rapid decelleration. The weight transfers to the
front which dives towards the ground. Front grip is often *increased* in
this scenario. Meanwhile, the weight comes off the rear end which lifts
skyward. Traction is reduced and the rear tires tend to lock first.

> 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).

"Proper" bias necessitates mechanically setting the front brakes to perform
the majority of the braking force given the inevitable weight transfer. With
many environmental and mechanical variables considered, this bias is set to
create the desired (not necessarily best) stopping and handling performance.
This is a subjective matter often decided more by lawyers and accountants
than driving enthusiasts.

Meanwhile, optimal braking is never achieved by violently stomping on the
brakes. A smooth modulation of force is best -even when ABS is there to bale
one out electronically.
--
Scott F. Williams
NJ Scirocco nut
'99 Subaru Impreza 2.5 RS
Mazda 323 GTX turbo "assaulted" vehicle
Golf GTI 16v "rollycar"
ClubVAC: "Roads found. Drivers wanted."



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