You can never have to much brake! The more the better!
Photography Credit: Tom Suddard
It’s a powerful message that every driving instructor, not to mention every high-performance parts vendor, should have told you a million times: Brakes are the most powerful and effective speed-changing device on your car. Regardless of what you drive, or how much power you have under the hood, the quickest way to alter your velocity will always be via the middle pedal.
[How to Go About Upgrading Your Brakes]
So it stands to reason that any competent high-performance build should focus on braking performance as a key factor in lap times. Plus, brakes aren’t just something that slows a car from x to <x. On a fast lap, the brakes are used to not only shuck speed, but to balance the chassis as well, transferring load from one end of the car to the other.
Brakes are important, is what we’re saying, so good brakes–brakes that not only give you great stopping power, but great feedback, durability, predictability and repeatability–are a required tool for a proper track machine.
Motion to Heat
Let’s take a look at what brakes actually do. Yes, they slow your car, but when you think a little deeper about the physical processes involved, you gain a bit better understanding of how important brakes are in a high-demand environment.
At their core, brakes are energy-transitioning devices. A car in motion possess a lot of kinetic energy, and safely getting that car through a corner is often going to require shedding some of that kinetic energy in order to reach the proper entry speed.
But thanks to the first law of thermodynamics–hopefully you weren’t asleep or high during the literal first day of physics class–we know that a car’s kinetic energy can’t simply be “shed;” energy in a closed system must remain constant. It can’t be created or destroyed, only turned into other types of energy.
We could, for example, turn the car’s kinetic energy into sound energy. But chances are that you’re not racing a submarine, so that sound would travel through the air, and air is a very efficient conductor of sound waves. Efficiency means a lot less energy is required, so it will take a long time to turn the required amount of kinetic energy into sound. And while entering a corner to a screaming guitar solo or sick bass drop would be awesome, you’d need to produce several hours of “Stairway to Heaven” in order to hit your target entry speed–pray for a long, long braking zone.
We could turn it into light energy, but again we face the same problems. Light energy is not only pretty efficient, most of what we actually know as light is a byproduct of heat energy. Case in point: Most old-school incandescent light bulbs turn only 10-20% of the energy put into them into light. The rest turns into heat radiating from the glowing filament.
Why not skip the middleman and turn that kinetic energy into heat energy? It takes a lot of energy to generate heat, and heat is fairly easy to disperse through convection and radiation. So that’s our plan. Good talk.
Hot, Hot (Hot)
Before we get into the nuts and bolts of the particular brake kit we used, let’s talk a little about how much energy we’re actually trying to deal with here.
Our 3100-pound Corvette possesses about 1.4 million joules of energy while traveling at 100 mph. That’s roughly enough energy to run an entire household’s electricity load in the dead of summer for about 20 minutes. Slowing that mass to 50 mph for a single corner entry requires converting about 15 minutes’ worth of that light, a/c and Xbox time into heat. (Remember, energy increases by the square of the speed, so small speed increases produce correspondingly larger energy increases.)
During an average track day or time trial session, your car’s brakes can easily convert enough kinetic energy to run your entire home for a full day and night. That’s a lot of kinetic energy to turn into heat. Brakes–especially those on fast, heavy cars–are doing a tremendous amount of work and operating under immense thermal stress.
Just as important as how well a brake system applies pressure is how smoothly and predictably it releases pressure. Predictable and consistent brake release is extremely important for effective trail braking and mid-corner speed adjustments. The Wilwood kit excels in this area. Photography Credit: Dave Green
In order to most efficiently turn that kinetic energy into heat, brakes use friction–in our case, it’s the friction of brake pads being hydraulically squeezed onto an iron disc. The greater the friction, the faster the heat builds and the faster the kinetic energy is converted. End result: The car slows thanks to the physical interaction of two surfaces trying to occupy the same space at the same time.
Once we’ve transitioned that kinetic energy into thermal energy, that thermal energy has to go somewhere, right? First law of thermodynamics and whatnot says so.
Air flowing in and around the brake components works to disperse that heat into the surrounding atmosphere, but heat is also transferred to the brake components and anything that touches them–so stuff like hubs, wheels and uprights see a lot of thermal load as well.
In other words, it’s a wonder brakes work at all. They deal with immense thermal and physical forces hundreds of times per track day, so having an efficient, reliable setup is paramount to proper performance.
Nuts. Bolts.
What was the problem with our stock brakes? We’d call them barely adequate–fine for autocross, but pretty substandard for any track use. They exhibited fade even with better pads fitted, and that’s surprising for a machine that is supposedly a world-class sports car. We needed better, so we peeled open the Wilwood catalog.
Why Wilwood? They offer aftermarket brakes that are already performing well on tracked Corvettes. Up front we installed their Aero6 Race kit, which matches six-piston anodized aluminum calipers along with two-piece, 14-inch-diameter rotors that feature aluminum center hats. This kit is an aluminum-hatted version of the one mandated in the Spec Corvette series. In other words, that same architecture has seen countless laps around race tracks inside C5 Corvettes being driven at 101% and beyond. We figured that the design certainly has a solid performance pedigree.
Our kit, though, gets two-piece rotors: iron outers floating on aluminum centers. The aluminum centers help lower the unsprung, rotating mass, while T-slot fasteners accommodate the different expansion rates of the two materials.
The Wilwood big-brake kit for our Corvette marries lightweight aluminum center hats with traditional iron rotors. To prevent warping, the hardware that joins the two components rests in slotted channels. Photography Credits: J.G. Pasterjak
The downside of floating rotors–if there is one–is that their unfixed nature can mean a little bit of a rattle when there’s no brake force being applied. It’s hardly a deal-breaker when you feel the performance, though.
Out back we installed Wilwood’s Superlite four-piston kit. It features four-piston, anodized aluminum calipers clamping down on 12.9-inch iron rotors which again float on aluminum centers.
The rear kit features four-piston calipers. Both ends use pads that are a meaty 20mm thick. Photography Credits: J.G. Pasterjak
The wider diameter of the new front and rear rotors results in a big pickup in the swept area of the pads against the rotor. More swept area means more friction, which equates to the ability to turn more kinetic energy into heat energy quicker. More area on the rotors also means more surface area for heat radiation.
The front’s 14-inch-diameter rotors see a full 75 square inches of swept area, which is a 10% bump over the stock 13.5-inch-diameter pieces. We gained even more area out back, as replacing the stock 12-inch rotors with the 12.88-inch Wilwood pieces increased swept area from 43 to 59 square inches–a 37% bump.
The additional swept area in the rear also serves to throw a little of the proportional brake bias toward that end of the car. With the rears now doing a little more work, trail braking becomes more precise and intuitive as the Wilwood brakes allow the cornering loads at both ends of the car to be more precisely adjusted.
Installation of the Wilwoods is quick and easy. Attaching the floating rotors to the hats takes a hot minute, especially if you take advantage of the drilled bolt heads and safety wire all of the fasteners–which you really should do. (At the very least, apply a high-temperature thread-locker. But, really, you should safety wire as the ultimate safety precaution.)
Make sure that you have a good set of 12-point sockets on hand, though, as this kit features several high-strength 12-point bolts and nuts. The front kit features six-piston calipers. Photography Credits: J.G. Pasterjak
As for installing the rotors and calipers, it’s barely more complicated than replacing the stock pieces. Budget two to three hours for the entire job. Adapters attach the Wilwood calipers to the stock hubs, and some shimming might be required (the shims are included). In the end, it’s a simple process requiring a bit of trial and error and the removal of two bolts per corner.
Once in place, the new brakes fill the wheel wells with a lot more authority than the stock pieces. They’re so large, in fact, that they’ll require the use of at least 18-inch front wheels. To fit some 18x10.5-inch Z06 wheels up front, we had to employ a 1.5mm spacer. We also found that thick wheel weights got in the way, so closely does the inner diameter of the wheel hug those new calipers. In the rear, the 12.88-inch diameter discs easily fit inside 18-inch wheels.
On Track
Our braking system upgrades worked a transformation on the Vette. Not only can we now easily trail brake and set the attitude in corners, but the absolute braking force that these Wilwoods can produce is nothing short of astounding. The pedal feels quite a bit lighter than before–that takes a bit of getting used to–but our foot quickly recalibrated to the new hardware. The action feels linear and intuitive.
Wilwood supplied our kit with a set of BP-30 SmartPads. They’re listed as a race pad, yet seem to require very little initial heat while also providing great feedback.
Perhaps most impressive has been the durability of the entire setup. Since installation, we’ve run time trial events at NCM, Roebling Road, Sebring and Daytona, as well as a dozen or more autocrosses, and we’ve barely worn off a millimeter or two from the 20mm thick front pads.
Brake It Down
The Wilwood setup on our C5 Z06 will set you back a few bucks. The front kit retails for a little more than $2800, and the rears go for around $2000.
It’s real money, but these brakes are also doing a real job. Stomping the pedal at minute 2 or minute 25 of a track session produces the exact same throw-out-the-anchor result, lap after lap, event after event. Balancing the chassis with the brakes, whether at a 55-degree February autocross or a 95-degree August track day, is always intuitive and confidence inspiring.
You can never have to much brake! The more the better!
Can I use the 18" rear factory Z06 wheels in the front with the Wilwood kit you used on your project C5 Z06? Will I require spacers; if so, what size?
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