[ST] RE: Rear Brake

["Keith Tynan" <keith@xxxxxxxxxxxxxxx>]

> Date: Mon, 19 Feb 2001 16:56:48 -0600
> From: "Robert Fastner" <bobfastner@xxxxxxxxxxxx>
> ...
>     Hearing a lot of denial here. So you don't use your back brakes eh?
> Maybe you should ask Triumph to leave them off. I think you'll find that
> using them decreases your stopping distance in emergency situations.
>
> Date: Mon, 19 Feb 2001 21:39:16 -0500
> From: "Joel Ashman" <joel.ashman@xxxxxxxx>
> ...
> I'll second the necessity to use the rear brakes.  They provide something
> like 30%-40% of your stopping power.  And they help to keep the front from
> diving.  Heck, when I took my cycle test in Virginia, the instructor
> specifically looked to see if I was using the rear brake.  It would have
> cost against my score had I not.
> ...

Hey Bob, this is a tease, right? :-)

As some listers might've already deduced, I'm an advocate of deriving or
substantiating the method from a thorough understanding of the physics of
the situation, rather than trying to constrain individuals on a 'need to
know' basis. (BTW I am a UK IAM member (=police instructor tested), and
regular IAM club rider.)

There're two sides to this coin: one is the *EMERGENCY* situation - when
it's a case of either stop short or die, and the other is normal braking,
when the situation's not nearly so life threatening.

When braking, the front starts out by doing around 50% of the work. Once
applied, this figure rapidly escalates towards 100% as more pressure is
applied to the lever. At the back it's a different story; this starts out
with about 50% and rapidly decreases towards zero as more and more weight is
off-loaded onto the front. So to get maximum braking, we have to increase
the pressure on the front, at the same time decreasing the pressure at the
rear (from an initial pressure close to lock-up).

Research* has shown that in practice, these two conflicting activities
demand too much concentration. Maximum braking using front and rear brakes
invariably means locking the rear wheel, with a consequent loss of
stability. The following figures were achieved by a Kawasaki ZX9R from 100
km/h (60 mph):

Solo - front only    40 m (131 ft)
Solo - front & rear  38 m (125 ft)
Solo - rear only     95 m (312 ft)
2-up - front only    41 m (135 ft)
2-up - front & rear  43 m (141 ft)
2-up - rear only     92 m (302 ft)

* Das Motorrad #3 1995 (1995/01/21)

To quote the source article:
"
It?s not the friction between the tyre and the road, but the  tendency of
the rear wheel to lift off the ground that affects the maximum braking
effect. In this case, all of the mass is place onto the front wheel, giving
little or no difference between retardation using the front or both brakes.
Using the rear brake alone gives only 40% of overall braking. These
conclusions pertain to optimal conditions only. With lower friction on wet
roads and with increased luggage loads, the rear brake can gain in
importance. But most important of all is the concentration afforded to the
front brake by the rider. The maximum brake pressure should be reached as
soon as possible - without locking the front wheel - since even the shortest
locking of the front wheel can lead to a fall. Tests with a sample of riders
show that this approach can save up to 8 m braking distance, when only the
front stopper is used. The rider should only apply the rear brake (in a
controlled manner) after the carefully judged application of the front. The
often suggested locking of the rear wheel brings no advantage, reduces the
already minimal frictional contact, and can, on wet roads, severely reduce
stability; a pearl of wisdom that racing riders have known for a long time.
One often sees them with dancing rear wheels, but never locked rear wheels.
"

I'll upload a little spreadsheet which demonstrates some of these
principles.

FWIW: On the road, I use both brakes as a matter of course, but front only
or rear only in special situations. On the track, I tend to use front only -
my expertise isn't sufficiently high to be able to drift the rear
(Haga-style) into corners!

Regards,
- --
BRG
email: keith@xxxxxxxxxxxxxxx
'00 Sprint ST BRG 'Wolfram'


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