Guide to S197 Brake Rotors
Author: Glenn Cope II
Standard S-197 Mustangs normally came with 11.5 inch front rotors which are small when compared to the larger 13.2 inch diameter as of 2012 models. The 11.5 inch front rotors typically require a 17 inch or larger wheel. However, if you upgrade to 14 inch rotors, they will require a minimum 18 inch wheel.
When braking, your carís weight is transferred to the front axle, requiring the front brakes to do most of the work stopping the car. Larger caliper pistons and more pistons will provide more clamping pressure on the pad and rotor. This increases stopping distance and overall braking performance. This, of course, is as good as the tires and suspension you have and their ability to transfer that brake torque to the road effectively. Your upgraded brakes may be able to stop you in a shorter distance but if your tires cannot handle the stopping power then itís a mute effort.
The Role of the Rotor
The rotor is essentially a radiator for your brake system. The larger the rotor, the better it cools. Aftermarket brake calipers come with 4, 6 or 8 pistons. More pistons or larger pistons result in greater contact from the pads to the brake rotors and create a more uniform friction surface. This will create a more stable brake pedal pressure, making braking force more precise and greatly enhancing pedal feel and braking confidence. The result is better lap times because you will have powerful and consistent brakes under the repeated loads of track use.
Advantages to Aftermarket
Aftermarket brake rotors could also feature improved vane venting technology, which improves cooling and increases resistance to cracking from thermal stress. What most people are familiar with are the slots and or cross drilled holes. These holes or slots in the braking surface help dissipate heat and eliminate brake dust and gases.
Why Slotted Rotors?
Slots in rotor faces are partly a carry-over from the days of asbestos pads. Asbestos pads were prone to surface glazing and the slots tended to help scrape and de-glaze them. Similarly, cross drilling the rotor helped by providing a way to expel the gasses created when certain bonding agents employed to manufacture the brake pads began to break down at very high temperatures. This condition was referred to as out-gassing. When it did occur, the driver could still feel a firm brake pedal, but a large reduction in pad friction. This normally only happened at temperatures experienced in racing. However, with modern race pad technology, out-gassing is no longer an issue with pads designed for racing. With that said, slotted rotors are still advantageous to dissipating heat and is a must-have for anyone who plans on navigating road courses.
At the end of the day when it comes to buying aftermarket rotors that are cross drilled, slotted or both for your Mustang, just know it is for an aesthetic value, as well as heat and a slight weight reduction. If your Mustang is going to see a race track then slotted is the preferred choice. With certain pad compounds slotting can help wipe away debris from between the pad and rotor in turn increasing the quality of friction between the rotor and the pad.
Why drilled Rotors?
A cross drilled rotor has a similar benefit, but is more susceptible to cracking under severe stress. For street and occasional light duty track use, they will hold up fine. One good street benefit of both cross drilled and slotted rotors is that they break up the water film forming when driving in wet conditions. This effect is most evident with cross drilled rotors, due to water flowing through the holes. It should also be noted, most aftermarket brake rotors are zinc plated. This improves corrosion resistance and also gives the rotor a nicer look because of its oxidation resistance.
Another option you will see is dimpled rotors. This has the same effect as cross drilling but not the weakness of drilling. When you buy a new set of rotors you will want to bed or burnish them in. You do this by making 8-10 60 MPH to 5 MPH stops. You will Start to smell your brakes. This puts a layer of brake pad material on the rotor. Now your friction power is maximized and you can enjoy your new rotors.