Technology Spotlight: AP Racing Strap Drive Brake Rotors
January 7, 2010
This Strap Drive System has been developed by AP Racing both for Road and Race applications. The standard fitment brake discs on many performance cars can suffer from brake vibrations caused by disc distortion. This generally occurs on fast road and track installations.
On many performance cars the typical standard brake disc will be a heavy duty ventilated single piece casting. Couple this type of rigid disc to a standard hub and wheel bearing and the result is any hub distortion / run out will transfer onto the disc brake faces. This eventually results in brake vibrations, usually picked up through the steering wheel.
The AP Racing Strap Drive System offers a new take on the floating systems already in the market place. Strap Drive uses a series of stainless steel straps to locate the disc to the mounting bell, producing a flexible coupling between the hub and the disc faces. This allows the disc to run true in the caliper under all conditions and also permits the disc to expand and contract without being restricted.
Some current replacement discs in the market place have evolved from Motorsport applications, they typically use a drive bobbin to provide some disc float and were devised to reduce pad knock off on race cars. This system can work on a road application but there are some major drawbacks that the Strap Drive has overcome with its simplicity.
Bobbin float discs rely on a series of drive bobbins moving freely in drive slots. This movement can create wear during service and promote noise. The slots can fill up with road / brake debris causing them to seize. AP Racings strap couplings can’t suffer from any of these drawbacks. Therefore Service life, brake noise and also brake pedal travel are all improved.
- Compared with single piece discs the disc is de-coupled from hub, this allows disc to align itself perfectly within the caliper.
- Improved pedal feel and brake response as a result of improved disc alignment within caliper.
- Improved pedal feel at elevated temperatures as disc rotor is able to expand in a controlled manner with little influence from the disc mounting. This greatly reduces disc coning.
- Controlled axial float of disc rotor reduces brake ‘knock-off’ which can result in an inconsistent pedal feel.
- No free moving parts means that the wear problems normally associated with floating disc designs is not present.
- No free moving parts means that there are no clearances to become clogged with debris and corrosion which would prevent a conventional floating disc from operating correctly.
- No free moving parts means no unwanted mechanical noise from discs.
- Disc rotor and strap sub assembly available as service item for cost effective servicing.
- Successfully used in race applications.
Important note: When replacing brake pads with strap drive discs fitted, do not push the pistons back in to the caliper by use of a lever against the discs. If this is done then the disc straps may be distorted and this can cause disc runout, resulting in possible brake vibration.