October 2, 2009

In part one of our brake buyer's guide last month, we introduced you to a wide variety of companies that specialize in upgrading the braking system of your Mustang or Ford. This month we complete the story with another great batch of companies that offer everything from mild to wild. As enthusiasts whose formative years included the dark ages that considered a Lincoln Versailles rear disc upgrade as the cat's meow, we're grateful for the variety of products these companies represent. Dig in, eat it up, and revel in the performance paradise we've grown to take for granted of late. It hasn't always been this way!!

Bigger Is Better?
Prevailing wisdom follows the bigger is better axiom, but we dug a bit deeper into the subject by discussing brake theory with James Walker, Jr., author of SA Design's High-Performance Brake Systems. Beyond currently serving as a consulting engineer for StopTech, Walker heads up scR motorsports, and in the past 15 years has been employed in brake system design, development, and application engineering at Kelsey Hayes, Delphi, Bosch, GM, and Ford Motor Company. Yep, needless to say Walker's knowledge of the subject far surpasses our own, and we appreciate him sharing his thoughts.

Walker outlined what he feels to be the three most pertinent reasons for considering bigger brakes than the factory provided, 1) improved heat absorption and dissipation--with a corresponding improvement in fade resistance, 2) improved rigidity/reduced compliance through braided lines and stiffer calipers (resulting in a firmer, more responsive brake pedal), and 3) improved curb appeal. Walker's list is clearly in order of importance from the racer or open tracker's perspective, as keeping brakes within target temperatures is paramount to effectiveness, consistency, and a competitive edge. Bling is last on the list for the hard-core enthusiast, and yet we recognize that many brake systems are bought with aesthetics as a primary motivator--no judgment here, just an observation.

The role of the tire is frequently overlooked in the quest for improved brake performance, but Walker's book devotes a whole chapter to the subject. The ability of the tire to provide enough traction prior to lockup is arguably the biggest factor in the overall scheme of things, because as Walker proclaims from atop his soapbox, "The tire stops the car." Exceed the tire's traction capacity, and any extra braking power becomes totally useless. As Walker puts it, "If you have enough torque to lock up your brakes, you have all the torque you need." Oversimplified? Sure, because most, if not all factory systems will do this if pushed hard enough--at least until they get hot from repetitive use, which brings us right back to Walker's number one reason for considering the bigger brakes--heat absorption and dissipation.

In the end, you want to determine the equipment which is necessary to achieve your performance goals, rather than going overboard with the biggest combination possible. Bigger really isn't always better, for "bigger" almost always equates to "heavier." Weight is an enemy in virtually all performance applications, all the more when it is unsprung and rotating, increasing inertia forces. In short, the reality is that obtaining adequate and repeated brake torque with the smallest (read lightest) equipment that will do the job, is optimal.

Conspicuously absent from Walker's short list is reduced braking distances--what many would presume to be a given byproduct of bigger brakes. Not so says Walker, returning to his point that having enough brake torque to lock the tires is indicative that the chassis already has maximum usable torque--though not necessarily enough thermal capacity for extreme duty conditions. If tire parameters remain the same before and after a brake upgrade, stopping distance changes are unlikely with one caveat: the increased thermal capacity of the bigger brakes should enable your stopping distances to remain constant due to good heat dissipation, rather than increasing due to brake fade.

When pairing wider/stickier tires with more powerful brakes, decreased distances may be possible, but there is another factor to consider--driver comfort. As Walker explained, "If it takes, say, 50 pounds of driver leg force on the brake pedal to get typical stock tires to lock with stock brakes, it will probably require 80 to 100 pounds of brake pedal force to get good race tires to lock with the same brakes." While this means the stock brake system most likely can still generate the maximum usable brake torque, such extra physical effort will likely result in driver fatigue. In this case, changing the leverage in the system, i.e. through a larger rotor/caliper combination, could be worthwhile simply for reducing driver effort. Other reasons to consider an alternative braking system, particularly on a vintage vehicle, could include improved serviceability, lighter weight components, and broader selection of brake pad compounds.

We learned much from a few minutes of conversation with Walker--far too much to share in such minimal space. We look forward to a thorough read of his book, and suspect many of our readers would find it of considerable interest as well.