How Forces Work within Your Braking
System
Your brake fluid is pressurised by the INPUT
FORCE you apply to a piston contained within
the master cylinder. Both your front and rear brakes have a
separate system with their own master cylinders. The piston
moves within the master cylinder which is sealed to prevent
fluid leaking out or air entering into the system.
There is air on one side (the outside) of the
piston and hydraulic brake fluid on the other side (within
the sealed system). For the piston to work efficiently, it
must move with the minimum of friction. There is a rubber seal
between the piston and the outside of the cylinder and often
a rubber boot as well. Keep these well lubricated to minimise
friction.
The amount of pressure exerted on your brake
by your system depends on how much FORCE you
put on the piston.
F (Force On Piston) / A
(Area Of Piston In Sq In) = Hydraulic Pressure (PSI)
If the piston in your system has an area of 1 square
inch and the FORCE is 200lb then the pressure
is calculated using the formula as follows :
200lb / 1 square inch = 200
psi
A smaller piston gives a higher pressure. If you replaced
the piston with one with only a 1/2 sq inch area in the same
system with 200lb of FORCE then the pressure
exerted is 400 psi. You can use your piston size to change
the pressure within your hydraulic system, but it is a complicated
business and you should seek professional advice.
A simple hydraulic braking system on a motorcycle is shown
below. The pistons in this system have two different surface
areas with the master cylinder piston having a surface area
of 2 sq inches and the piston in the caliper has a surface
area of 4 sq inches. With 400lb of FORCE being
applied to the master cylinder the piston produces 200 psi.
Basic physics operates on the system following two principles:
- Hydraulic fluid cannot be compressed to a lesser volume,
no matter how high the input force
- The resultant pressure with the system is equal over
all the internal surfaces of the containing system
When considering the hydraulic principles outlined above
we know that the 200 psi in our example system will act equally
on all surfaces within the system. The shell of the master
cylinder, the shell of the slave cylinder and the connecting
hose will all have 200 psi acting upon their surfaces, however
they are fixed and cannot move. The only element within the
system that can move to accommodate the increased pressure
from the master piston being pushed in is the slave piston.
This will move and will have the same 200 psi acting upon it.
If the slave piston in our example has a 4 square inch surface
area the FORCE it produces will be 800 lb. The area has doubled
so the FORCE is doubled. 400lb of FORCE is pushed down onto
2 inches squared which then acts upon the 4 inch square surface.
We must remember that only the FORCE changes in this system – the
pressure remains the same at 200 psi. This is 200 per square
inch so with the other piston having 4 square inches the FORCE
produced has twice the surface area to work upon and so twice
the FORCE in lbs.
To increase the FORCE on the caliper piston we can decrease
the area of the master cylinder piston area or increase the
surface area on the caliper piston. The reverse is true to
decrease FORCE on the caliper piston. We can either increase
the area of the master cylinder piston area or decrease the
surface area on the caliper piston.
The rubber hoses that come as stock on most production bikes,
do 'give' or swell with the increase in pressure during braking.
As a rider your feel this as a softness or spongy
braking. This problem gets worse with older hoses and more
powerful braking. You can fix this problem if you replace the
rubber hoses in your braking system with aftermarket stainless
steel braided hoses.
This problem exists because the pressure within the braking
system acts on all the surface areas of the braking system
including the brake hose. This pressure when pushing outwards
on a rubber hose can cause the hose to swell under heavy braking.
The pressure is constant so you will still have the same pressure
acting on the caliper piston BUT the amount of movement the
caliper will have is reduced due to the amount of movement
within the hose and also the FORCE acting upon the caliper
will be reduced due to some force being used up swelling the
brake hose. The result - your brakes feel less powerful and
less crisp.
We know that by decreasing or increasing parts of the system
you can alter the FORCE produced at the slave caliper but
that does not increase pressure within your brake system. Pressure
is the constant within the braking system and cannot be altered
internally - you just have to pull harder or change your lever
ratios! If you can produce 200 psi at the master cylinder hydraulic
law requires that 200 psi is produced at the caliper!
Top Tips for improving braking performance:
1. Fit oversize front rotor discs - see "how
hydraulic brakes work" tip sheet for more info or visit Talon engineering for
more information.
Talon
Brake Parts
2. Replace stock hoses with stainless steel braided hoses.
We recommend HEL performance brakes. Use the link here to learn
more.
HEL
performance brake lines
DISCLAIMER! The
information offered here is an introduction to the
principles and parts of your motorcycle's braking system.
Reading this top tip will not turn you into an expert
brake mechanic! If after reading this page you feel
inclined to carry out alterations to the braking system
of your bike we will not accept responsibility for
what happens next! You are responsible for your own
actions and this page has been made available online
only to offer an introduction and to give you a greater
background understanding of how your braking system
works, what affects any changes you make may have and
what the different elements of the system do. If
you are in any doubt about the braking performance
or maintenance of your braking system consult your
local dealer.
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