From: jlevine@rd.hydro.on.ca (Jody Levine)
Subject: Re: ZX-11 front brake.
Organization: Ontario Hydro - Research Division
Date: Wed, 18 Nov 92 23:07:35 GMT

In article <1992Nov18.150911.24658@exu.ericsson.se> lmcstst@noah.ericsson.se (Stamos Stamos) writes:
>
>I can lock the front wheel of my ZX no problem, in fact it's too easy 
>to lock up the front wheel. 

I would say that this could stand improvement, no?

>A ZX is much heaver than a CBR900, but then again someone in
>rec.autos posted some formula on braking distances and he claimed that the
>weight of the vehicle didn't affect the distance(what he actually claimed is
>that the greater weight of a car would allow it to create larger braking
>forces thus canceling each other out). How does this apply to bikes?

Yes and no, minister. Naively, the heavier the vehicle, the more down force
you have, and since traction is related to down force (no, in real life it
is not truly linear) then you should be able to get *similar* stopping
distances. For an exactly scaled tire/road system, yes, it would be the same,
but this does not exist, which is why it is not really linear. Even if it 
it were, the heavier vehicle would require a larger braking *force*. 

In practise, stopping distance depends on how good your tires are, what's
on the road surface, how fast you're going, how good your brakes are in
terms of grab, ease of modulation, the ratio of braking forces to each
wheel, and of course, the skill of the operator or the sophistication of 
the ABS.

Sports cars with ABS stop in the shortest distance (Motorcyclist). The 
average biker stops better than the average cager (riding course). Trucks 
don't stop very soon at all.
>
>If two brake systems(for the same bike) both have the power to lock the 
>front wheel but one is better, what is it that makes it better/stop in a 
>shorter distance?  Isn't the front tyre(and suspension) the limiting factor??

That sets the limit, the other task is to find it. How easily you can find 
the point of almost-lockup, where you have the most braking force?
If your brakes grab or are too sensitive (or not enough), it makes it harder.

>Is it the feel of the brake that allows you to use maximum pressure without 
>locking the front? 

This is the bottom line.

>Is it the lead time of the pads from when you first pull on
>leaver to when they really start to grip? 

If you have nothing nothing nothing then lots lots lots, then your brakes are
grabby and difficult to control. This is part of feel.

>Is it because greater
>effort is needed at the leaver at higher speeds?  

This is inevitable. You need more force to shed speed faster.

>How does the friction
>of the pad come into play, apart from needing more/less pressure on the leaver?
>I know about brake fade but that is more applicable to the race track, or is it?

The friction of the pad/rotor system is temperature dependent. The idea 
of eliminating fade is to keep this temperature dependence to a minimum, 
yet to have enough friction to do the job (fadless brakes would be useless 
if they didn't work well to begin with).

Let the flamefest begin.

I've        bike                      like       | Jody Levine  DoD #275 kV
     got a       you can        if you      -PF  | Jody.P.Levine@hydro.on.ca
                         ride it                 | Toronto, Ontario, Canada