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Wilwood Rotors

Rotor Performance

Wilwood Engineering produces over 120 different types of high performance rotors designed specifically for racing applications. Although a rotor’s basic function is to disburse energy (in the form of heat) created by the brake pads clamping onto the rapidly rotating rotor, how well a rotor performs this job under the extremes of racing is why Wilwood rotors are considered the best in the industry. 

The key elements involved in a high performance rotor are: 

What is the mechanical advantage of the rotor (diameter)?

How stable (resistant to cracking) is the rotor material during thermal cycling (the continual process of heating and cooling)?

How stable is the rotor material when thermal shock occurs (the large, sudden, rapid change in rotor temperature)?

How efficient the rotor is at disbursing heat caused by friction between the rotor and brake pad?

How light the rotor can be made and still perform the task required (rotating weight not only contributes to unwanted unsprung weight, but also rotating weight)?

Wilwood engineers address these critical questions and others when designing rotors. Because race cars differ in their braking requirements, Wilwood has developed both specific designs and specialized materials and manufacturing techniques to accommodate different performance criteria.

Wilwood vented rotors are designed for maximum cooling. The internal vanes pump cool air from the center of the wheel and take heat away from the rotor, allowing rotor temperatures to decrease. Wilwood has designed special curved vane and straight vane rotors to effectively move large volumes of air to rapidly disburse this heat (energy).

Specially formulated iron is used to enhance the stability of the rotor, while allowing difficult castings in complex vane configurations to be produced. Wilwood’s proprietary casting techniques are the result of over 20 years of vented rotor research and development combined with actual on-track performance evaluation. All rotors are precision machined to assure surfaces are flat and parallel. 

For all rotor designs, Wilwood conducts extensive in-house dynamometer testing to measure results of rotors under the most demanding conditions, This unique testing, teamed with extensive research and development and track testing assure the racer of the best quality high performance rotors available. 

Rotor Bedding

All new iron rotors should be bedded-in before being used under racing conditions. Proper bedding-in will prepare the rotor surface, prolong the rotor's life and make it more resistant to thermal checking or cracking under severe braking conditions. The following procedures should be followed when bedding-in rotors: 

•Thoroughly inspect all brake system components before proceeding to track. Check all bolt connections, make sure mounting bolts and rotor bolts are properly lockwired, that brake pads are properly secured by retaining clips or cotter pins, that master cylinders and brake pedals are working properly, that brakes are properly bled with plenty of fluid, and that proper engagement of brakes occur when pedal is depressed. 

•Because the bedding process is different for rotors and pads, it is best to bed-in a new rotor (disc) using a used set of pads,  preferably ones which will not create heat rapidly. Generating heat too quickly will thermal shock the rotors. Likewise, when bedding-in a new set of brake pads, use a used rotor. This new-used bedding process permits controlled bedding of each individual component. 

•Make sure that the rotor surfaces are free from oils, grease and brake fluid.  

•Close air ducts approximately 75% to expedite the bedding-in process. 

•Run vehicle up to moderate speed and make several medium deceleration stops to heat up the rotor slowly. This will help reduce the chance of thermal shock caused by un-even heating of the rotor. 

•Pull into the pits and allow the rotor to cool to ambient air temperature. 

•Do not hold brakes on after performing the bedding-in procedure until cooling is completed. This will avoid “hot spotting” or un-even cooling which can damage the rotor.  

Rotor Runout

Rotor runout should be adjusted as soon as you receive your Wilwood components. Wilwood rotors are precision machined to ensure the rotor surfaces are flat and parallel. Sometimes hubs, bearings or other components have runout that cause the rotor to runout. As a rule of thumb, allowable runout should be .005” - .008”. Adjust the runout by re-indexing the rotor or by placing shims between the rotor and hub, or hat. Runout should be rechecked regularly. You can assume the runout to be acceptable as long as you are not experiencing brake drag, pedal oscillation or excessive piston knock back. 

Rotor Wear

Rotors will eventually start to show signs of wear; how fast depends on the type of racing, the frequency, and the brake usage. Grooving and/or cracking due to severe heat and thermal cycling indicate the rotor should be replaced. Note that surface checking itself is not a sign a rotor needs replacing as this can occur on iron rotors. Always replace rotor mounting bolts and lockwire whenever replacing rotors, taking care to inspect mounting hats or hubs for signs of abuse.