Honda Motorcycle Service Manual page 281

BRAKES
In single push type calipers, both pads press against the brake
disc through a reaction of the sliding caliper yoke. Calipers of
this type with single piston are more common on earlier Hon-
das. More current models use a single push type, but with dual
pistons (both on the same side).
Opposite piston calipers are most often used for road racing
motorcycles today. They do offer some improvement in per-
formance, but at great increase in cost and complexity. I n this
type, pistons facing each other on opposite sides press the
pads against the disc.
The amount of braking force available depends on the
magnitude of force pressing the pads against the discs, the
size of the contact area between the brake pads and discs, the
distance between the center-of the wheel and the center o f the
brake pads, and on the outside diameter of the tire.
Rectangular brake pads were introduced to increase the area
of the pad against the disc. But it was found that these pads
do not press against the disc uniformly, so the braking force is
not as effective as it could be. Hence, the dual piston caliper
was introduced so that a large braking force and uniform
pressure against the brake pads is ensured. Some dual piston
calipers have different piston sizes t o further balance the brak-
ing force across the pad - the trailing piston being larger than
the leading piston.
AS previously touched on, increasing the area of contact bet-
ween the brake pads and disc increases the braking force. This
increased contact means increased heat energy. The increas-
ed heat energy requires greater capability for heat dissipation.
SINGLE PUSH CALIPER OPPOSITE PISTON
CALIPER
I
YOKE
EFFECTIVE DlSC DIAMETER
BRAKE DISC I
DUAL PISTON
With the exception of in-board disc brakes and the GLl5OO
I
front brakes, all brake discs are exposed. To protect them from
rust, the discs are made of stainless steel alloy.
Because the material the discs can be made of is limited, the
discs can only be made so thin in order to reduce unsprung
weight before thermal distortion of the disc becomes a
problem.
As the temperature of the brake disc rises, the disc expands.
Because the disc is bolted t o the wheel, its expansion is limited
and some degree of distortion occurs.
The VTR250, with its in-board front disc, uses a plain cast
iron disc since rust is not a problem. The design of the GL1500
front brake with its covered discs and calipers, transfers much
of its heat t o the cast, hollow wheel.
DUAL PISTON CALIPER
Date of Issue: Sep., 1988
O
HONDA MOTOR CO., LTD