Re: The Low-Down on Bike ABS, Linked and EVO Brakes

["Steve Makohin" <wateredg@xxxxxxxxxxxx>]

Hello Ben,

From: "Ben Barkow" <dr.ben@xxxxxxxxx>

> from Steve Makohin:
>>
>> In your search for why the best stopping power is attained just before
>> wheel lockup as opposed to during fully locked wheels (i.e., a skid),
>> realize this is not an "ABS vs no ABS" comparison, because ABS is well
>> short of keeping the wheels at the threshold of lockup. That's the reason
>> why there are some exceptional scenarios in which a really good braker
>> can get shorter stopping distances on a non-ABS bike than with an ABS
>> bike. But back to your statement: When you hit the text books in your
>> research, pay particular attention to "static" friction. That's for the
>> theory, at least.
>
> I'm puzzled about ABS. I had assumed that ABS action is triggered by a
> discrepancy between the speeds of the front and rear wheels. Therefore, it
> only comes into play when one wheel (or both!) is just an epsilon beyond
> the point of "gone beyond" relatively-static-like rolling friction which
> is, I thought, already beyond the point of maximum grab of the pavement
> once a wheel starts skidding.
[...]

ABS varies, far and wide. Manufacturers are tight-lipped about the logic
behind their specific implementation of ABS. In short, without some serious
resources and reverse-engineering, it's very difficult to tell the details
behind the ABS logic (i.e., what are the exact conditions under which ABS
will cycle, and if it cycles differently, what are the different conditions
that trigger each specific type of cycling, and what is the exact nature of 
the cycling?)

In laymen's terms, I don't know if ABS cycles at the moment when front and
rear wheels spin at *slightly* different rates, beyond a threshold of
difference (e.g., 5% @ X mph), or some other condition. That's why I used
the somewhat vague term "when the ABS computer senses an 'impeding lockup'
condition". In other words, when the ABS computer (rightly or wrongly)
"believes" that a 'lockup condition' (however that may be defined) is in
effect.

I know you are an engineer, so you look at the precise facts (i.e., exactly 
how does it work?). To many people, bike ABS is like a toaster in some 
respects: As long as you know how to use it, who cares how it works? In my 
view, as long as people are well-versed in the appropriate use of bike ABS, 
the exact details of how it works are unimportant.. But I'm not an engineer 
:-)

- -Steve Makohin
 '01 R1100S/ABS
 Oakville, Ontario, Canada 

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