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Big Brakes, High Performance Pads and Rotors, and the Corvette

Wilwood, Brembo, SSBC, StopTECH, and AP Racing are a few of the big names that immediately come to mind when the phrase “Big Brakes” gets thrown around. What’s lesser known is that a large number of people misinterpret information like rotor size, drill patterns, pad material, and the number of pistons in a caliper. I’m writing this article to try and put a cap on some, if not all of these issues for the reader out in the world wide web of information. The goal is to try and explain some of these terms and concepts and their meanings to the best of my abilities, and narrow a couple of brands (maybe even one) down that seem to stand above the rest, in terms of fitting the needs of the new Corvette. But in order to do that, we must first understand the basics of braking, and how it is best achieved. Believe it or not, it doesn’t start with how big your brakes are…

It starts where the rubber meets the road. Literally- your brakes don’t stop your car, your tires do. Your tires are your first point of contact in the war against momentum. Think about it this way- if you can lock up your stock brakes, then you don’t need bigger brakes, you need stickier tires. This is the point of contact on the road for everything- turning, acceleration, and braking. But before you go out and purchase a brand new set of Mickey Thompson drag radials to run on the street, let’s briefly discuss a few basics on the tires. I am not advocating one tire supplier over another in this article, but the Tire Rack articles I reference happen to be some of the best tech articles on the internet for informational purposes. I’m sure most of you are well aware that each tire has a size to it. But, for those of you that don’t here’s a basic rundown of things to look for when choosing a set of tires. Size is obviously most important and is measured by width, aspect ratio, and rim size. This is stamped on the side of each tire in the width/aspect ratio/speed rating and rim size format. So a tire that is 225/50/R16 (like the one shown in the diagram from Tire Rack) is 225mm wide, has a 50mm aspect ratio to the wheel, is a radial tire and fits a rim size of 16 inches (tire size article here). The next most important piece of information for our purposes will be focusing on tread wear rating. Basically, in short the tread wear rating achieved on a tire is a good indication of how sticky a tire is. Plainly speaking, the stickier the compound the better the tire grips the road but the faster it wears out. This translates to having to replace tires more often, and wet weather driving should be approached with extra caution. So without writing a full tech article on how to determine all of these factors, I have provided another link to Tire Rack’s tech articles outlining each of these points (tread wear/ UTQG test standards here). So, now that you’ve gone out and bought the stickiest tire you could legally run on the street, (***It bears repeating once again that when purchasing tires, a general rule of thumb is: the stickier the tire, the lesser the tread life, and generally speaking the worse the wet weather traction is going to be. ***) you want your braking to be improved further. Understandable.

Press on eager eyes, press on.

Suspension is the next area I want to touch on briefly as well. I’m not writing a tech article on how to modify your suspension today, but think of it this way: your tires are only able to remain connected to the road as much as your suspension keeps them planted on the road. In short, your contact patch (the area that your tires are actually touching the road-generally less than one square foot); can only be efficiently used if it is firmly planted on the road. So, on the new Chevy Corvette (or any new car for that matter) this shouldn’t be an issue initially, but aftermarket springs and shocks go a long way in terms of keeping your car planted to the road firmly and more effectively. Factory suspension is designed to be comfortable and usually not maximized for the track. So, if your plans are to track the car, I strongly encourage upgrading the suspension for better handling and traction. The more effectively your car is connected to the road, the more the contact patch is efficiently used. The more your contact patch is efficiently used, the better the traction. The better traction is maintained, the better the braking. See? Great braking starts with great tires and great suspension.

Rotors: Cross-drilled vs. Slotted vs. Blank

Now I’ll move on to perhaps the biggest debate in aftermarket braking: rotors. I repeatedly hear people debating whether or not cross drilled is better than slotted rotors, or whether slotted rotors are better than blank face rotors and vice versa for each of those, or a combination of the two. This is not an easy debate to settle, but before I anger the World Wide Web, we should examine the strengths and weaknesses of each. Cross drilled, although they may be the cooler looking of the bunch, are susceptible to cracking under heavy use (such as track time). By drilling holes in something (this may be obvious…) the structural rigidity of said object is reduced (it should also be noted that it substantially reduces un-sprung rotating mass, but this is negligible compared to the downfalls stated later). Brakes work on the principle of friction, and when friction happens- the byproduct is heat. Rotor temperatures can reach upwards of 900 degrees Fahrenheit when used heavily on the street and occasional track days, temperatures on the track have been recorded for an F1 brake rotor generating heat in excess of double that at 1800 degrees Fahrenheit. So as these components heat up, they also cool down, expanding and contracting putting these stresses on normal metal or alloy components is harsh enough; let alone drilling them full of holes. So, after repeated use in these conditions, the weakest area of the rotor tends to give way to the stress. This is evident in the manifestation of cracking around the weakest area of the rotor: the holes. A prime example can be seen in the picture below. This can result in catastrophic brake failure, which not only can be dangerous to you and others, but be extremely costly to repair. When the big names in racing technology like Brembo, Wilwood, etc. recommend against using cross drilled rotors on the track, their advice should be heeded. The only exception to this rule I can see is when the manufacturer uses ceramic or carbon/ceramic brakes, a markedly more expensive option seen on the feet of Ferrari, Porsche GT series cars, and other high end supercars.

After ruling out cross drilled rotors as a serious track or heavy use option (in my honest opinion, I question why they are even still made as an aftermarket option) the next rotor face design most heavily debated is slotted rotors. Slotted rotors serve multiple functions in their design: they help to expel hot gases as they are generated against the face of the rotor and the pad, while simultaneously sweeping the face of the pad free of dust, and any (in the uncanny event) debris that might have been sucked into the rotor/pad braking surface. Slotting rotors also helps the “bite” characteristic of the pad- much in the same way drilled rotors have the same effect. Slotted rotors have been around for quite some time now, and have proven themselves to be a viable option over blank faced rotors. However, the reasoning behind a slotted rotor is the same as a drilled rotor without the apparent disadvantages, and has proven so in various forms of racing.

The next option is a blank faced rotor; this is structurally the strongest of the three discussed options. But a blank face rotor lacks the advantage of slots to help expel heat and debris from the pad and rotor area, effectively running hotter than the slotted rotors. However, a vented, blank face rotor seems to be the rotor of choice for most race teams. By venting the rotor, with vanes inside the rotor itself, the air in the surrounding wheel and hub is effectively impelled through the surface of the rotor itself drastically dropping temperatures on the rotor face. Many manufacturers have developed an excellent system, as seen in the cut away picture from StopTECH-the impeller design pulls air through the surface of the already drilled rotor aiding in cooling. It is a fact that the heat generated by the braking process must be dissipated. The rotor (disc) handles roughly 80% of this job; therefore any advances in cooling this component are of great benefit. Vented rotors were initially introduced by Ford on the GT40 in 1966. With this we should also note that cooling is a large part of effective braking. Although not practical for most street cars, large ducts are often used in race car design to aid in cooling brakes; less heat means longer life, and less wear.

 

Pads

Brake pads are another serious point of contention for many enthusiasts and racers. The brake pad itself is a shaped conglomeration of friction material bound to a backing plate usually made of steel. Pad material can and has been made of various materials including asbestos (not commonly used anymore for obvious health reasons), ceramic, Kevlar, copper, aramid fibers, and other various organic and semi-metallic combinations. For the sake of argument I will not delve deeply into the “best” pad or pad materials, but there are a myriad of companies that produce brake pads, and each generally defines the differences between common light economy car use, and those designated for heavy truck, street performance or race only abuse. Some commonly noted companies include Hawk, EBC, Porterfield, Project Mu, Brembo, and so on. Different pads are geared towards different goals, some value less noise over less bite, others value less dust over less noise, and others still are designed for maximum performance regardless of noise or dust. The choice in pad is almost as unique as the driver, but more importantly the goals the driver has for the car and its performance and how the driver likes the brakes to perform at a certain point. Some racers prefer a harsh initial bite, making braking less initially modulated; while others prefer a moderate bite to help them gauge modulation in extreme braking situations. Again, pad choice is as unique as the car and varies uniquely from driver to driver,

Calipers

Ahh, those big shiny, colorful, name bearing beauties we all see behind the wheels of the cars on the greatest circuits in the world, clamping down on massive rotors slowing the car in impeccable fashion. These beauties are engineering feats in themselves, and are the final product of months of R&D, reshaping, resizing, structurally balancing, and finally matched to the car for perfect clamping force distribution. That being said let’s delve into some of the different setups that calipers come varied in. There are many different configurations for a caliper that go into play in order for it to function at its maximum efficiency. Things like number of pistons in the caliper, caliper material, piston material, the brake fluid being used, the size of the piston(s), the weight of the vehicle, the intended use of the vehicle, etc. The list goes on for quite a while longer, but for our purposes I will explain very simply how the caliper functions. In a nutshell, the process goes as follows: your car has a brake fluid reservoir usually behind a brake booster/master cylinder. This master cylinder is connected to the pedal which pivots on an axis- acting as a lever. When you place your foot on the pedal and apply pressure, this lever (pedal) amplifies the force of your foot and forces fluid in the brake master cylinder and through the closed system traveling throughout the vehicle to each corner at the same time, expanding and driving the piston out of the cylinder in the caliper against the pad to clamp down on the rotor. A simple cutaway of a caliper is below courtesy of howstuffworks.com and for a further in-depth explanation of how disc brakes work, please click on the picture to link to the article.

Now that we know how a caliper works, let’s examine how companies reach a conclusion on which size rotor, what size caliper, and what size piston within the caliper to use, and how many of them. This is an extremely complicated process that focuses on the corner weight of the vehicle, and starts and ends with the factory braking bias. The engineers of each braking system from the factory, for every car and manufacturer, had to put the system/car through an extremely stringent series of tests. In order for the car to pass, it had to be deemed road worthy after hundreds of hours of testing and reevaluating and ultimately the approval from the DOT and other governmentally mandated safety laws. In reference to braking bias, it is logically apparent that when you brake, weight shifts forward, and say you had just slapped some no name (or-as popular in the sport compact world, taking a higher performance model and installing its bigger brake setup on the base model car) bigger brakes, and would actually find that your stopping distances increased. What? Bigger brakes taking longer to stop the car? That’s right; by upsetting the braking bias you upset exactly how much pressure the brakes apply to each corner. By installing a bigger rotor, with a bigger set of pistons, it might be setting the braking bias too far forward resulting in the undue amount of pressure being put up front with not enough bias in the rear consequentially creating longer braking distances.

Fluid and Lines

Fluid is an entirely big subject in itself, and for our purposes I will refrain from making extreme recommendations, but if I was to over broaden the subject and make a **GENERAL** recommendation, I would say that it would be safe to do three things regardless of brake set up. Initially, I would recommend first and foremost following the exact specifications of any brake kit manufacturer that you end up purchasing. The amount of time these companies have spent researching which fluid works best for their kits, and the components that they use in each kit (rubber seals, and different metal components of the system react differently with different chemical make-ups of different fluids). Secondly, for a performance application, avoid DOT 5 fluids as they are silicone based and more compressible over glycol-ether based DOT 3, 4, and 5.1 fluids. Thirdly, I would recommend bleeding your brakes 2-3 times a year, more if you drive hard or especially if you track the car, or live in a humid climate. But honestly, this is not an easily approachable subject for the amount of depth we’re going into for this article. But on the subject of lines, I am a firm believer in stainless steel braided, Teflon coated lines. They do not expand in the same way that factory rubber lines do, creating a stronger pedal feel with better response. Dollar for dollar, it’s probably the cheapest and most noticeable performance upgrade you’ll spend on brakes.

 

Summary and Notes on Fitment

So, how do we determine which kit is better for our new Chevrolet Corvette? There are a few big name companies with great kits on the market, namely Wilwood, Brembo, and StopTECH. These are all big names and can offer incredible quality, and superb fitment. They each are 6-piston front/4-piston rear kits with the options of either slotted, or drilled and slotted rotors. As discussed earlier, slotted is the better option when choosing high performance rotors. Each kit comes with a set of stainless lines, and requires a minimum wheel size of 18 inches. It should be taken into consideration also when purchasing a kit of this magnitude that these will be larger than the factory brakes, and wheel fitment is crucial. The minimum clearance for each of these brake manufacturers is 2mm. This is easily accounted for when you follow the brake manufacturer’s directions for test fitment. The manufacturer will provide a FREE template online to be printed out to scale and then applied to poster-board or cardboard and then cut out placing this inside the wheel and double checking measurements and fitment. Pretty straight forward and easy to do with the wheel obviously removed from the vehicle. I hope that this article has helped clear up some of the misconceptions on big brakes, and brakes in general.

 

 

 


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