is clear from our last race that the Electric Imp has too much power
and weight for our stock sized brake system. We can confirm this diagnoses
by the simple test of getting the car up to speed and slamming on
the brakes. The brakes do not have the ability to lock the race tires.
We can not utilize the full grip of the tires to slow the car without
a better braking system. We have tried same size racing brake pads
and rotors but we have reached the conclusion that we need more pad
to rotor friction area. This means bigger brake rotors and pads.
else being equal, the bigger the brakes, the quicker the car will
stop (up to a point). Bigger brake systems however, mean more unsprung
and rotating mass. This extra mass will require extra power to accelerate
and more brake friction to decelerate. Race cars spend relatively
little time braking and the rest of the time accelerating, so at some
point, the benefits gained under braking could be negated by slower
acceleration from the small weight (and rotating mass) increase.
goal is to have brakes that can quickly bring the race tires to lock-up
and continue to operate without loss of performance for the duration
of a 35 mile race.
stock rotor is solid and not very large.
stock caliper uses a single hydraulic puck to push the inside brake
pad into the rotor's inside surface. This pressure also pulls the
outside brake pad against the outside face of the rotor.
remove the caliper and rotor. We leave the ABS sensor ring for future
DAQ upgrades. The white holes are where the stock calipers bolt
replace the stock caliper with a Performance Friction two piece floating
rotor. It is substantially larger. This gives more surface area for
friction and more leverage to stop rotation.
two piece rotor consists of an iron rotor and a light aluminum 'hat'.
The hat and rotor are connected by pins that allows the rotor to move
very slightly towards and away from the center line of the car. This
should reduce drag by allowing the brake pads to push the rotor to
the optimum position between the inside and outside pad, so that when
the brakes are released, the pads do not drag on the rotor.
Performance Friction Subaru Big Brake kit is larger then we think
we will need and would require even larger diameter wheels. We calculate
a diameter that will fit beneath a 15 inch wheel and still allow full
surface area for the caliper / pad combination that we have chosen.
We have the rotors turned down on a lathe to that diameter.
larger than stock rotor requires moving the caliper outwards from
the axle. We fabricate an aluminum extender bracket that bolts into
the stock holes.
bracket bolts to the knuckle.
replace our stock calipers with Wildwood racing calipers. The Wildwood
have 4 pucks. Two pressing the pad against the inside face of the
rotor. Two pushing the pad against the outside face of the rotor.
Two pucks help press each pad more evenly against the rotor. The caliper
is aluminum and is lighter than the stock caliper.
decide on Performance Friction Race pads.
quick road test reveals that we can now, at least lock up the street
tires. Track testing will give us a more complete answer.