by Jeff Ritter
I'm going to share a little secret with you: As delivered from the factory, the brakes on your car are not capable of handling repeated lapping on a racetrack. They're also probably not very good for Autocross, drifting, or rally racing. I don't care if your calipers are painted red or gold, if you have gigantic carbon ceramic rotors, or if your car is advertised as being optimized on the Nordschleife. Do you know why your brakes are not up to the task of a serious thrashing as delivered? It's the lowest common denominator rule.
In the US in particular, manufacturers try to make every car as accessible to as many people as possible. That includes the guy who probably has no business being behind the wheel. Despite the hardcore enthusiast's wishes, that's why you don't see fixed-back race buckets in a stock Corvette, and why stiff, manually adjustable coilovers aren't standard issue on a 911. It's much easier to push a button in the cockpit. The same is true of your car's brake system. If a manufacturer delivered a 'track-day special' with an extremely noisy brake pad, there would be countless complaints and warranty-related service calls. The Nissan GT-R is a perfect example. The owner's manual clearly states that the car has high-performance brakes, and that they could make some noise. I was browsing one of the GT-R forums the other day, and of course there were a number people complaining about brake noise. Go figure.
So, how do manufacturers address this problem? They compromise, sometimes heavily. The fundamental dilemma of taking a street car on a racetrack is that it was designed to do so many other things besides going as fast as possible. A purpose-built racecar has no such identity crisis. The brakes fitted to your car as standard are one of the most glaring examples of this dilemma, and they're often the first vehicle system to wilt when leaned upon under heavy use.
What we want and need from a street pad is completely different from what we expect out of a race pad. For day-to-day street driving, we'd all love to see our pads have the following attributes:
- Never make any noise
- No dust on our fancy wheels
- Good cold bite on the way to work
- Effective in the rain and snow
- Last 100,000+ miles
- Never wear out rotors
When the weekend rolls around however, our priorities shift. We want our pads to have the following traits:
- Enough heat capacity to never fade after repeated lapping on a racetrack
- Predictable torque response for precise brake pedal feel and modulation
- No required bed-in or preparation
- Low compressibility for a rock-hard brake pedal
- Immediate release from the discs when we let off of the brakes
- No uneven pad deposits or scoring of the rotors
- Little to no wear as heat increases
See any differences between those two lists?
Unfortunately, most manufacturers err on the side of caution, and prefer to make the stock brake pads as docile as possible for the street. They know that one day your girlfriend or wife will take your Evo to the store, and she'll tell you that there's something wrong with your "screechy brakes." For the hardcore enthusiast however, the inherent performance compromises in OE brake pads are difficult to accept.
Therefore, our currently available options are as follows:
- Accept the sub-par performance of the factory pads during aggressive driving, and enjoy their docile manners around town
- Try to find a 'happy medium' pad that contains some attributes of both street and race pads
- Install a harsh race pad that performs well in motorsports but has no 'street-friendliness'
So, we have some choices to make. We must define the most important pad characteristics for the type of driving we'll be doing, and choose a pad strategy with acceptable compromises. We try to get as close to our happy medium as possible, based on how we use our car. Every situation is different.
Before jumping into specific pad selection, let’s first take a step back and look at the bigger picture. Understanding the material composition of the four basic pad types, and how those materials behave on our cars, will substantially narrow the sensible choices for any given driving condition.
Brake pads for street cars typically fall into one of four categories. These categories are defined by the pad’s fundamental composition: organic, semi-metallic, ceramic, and sintered.
Organic pads are made of fibers mixed with fillers and binding resins to hold them together. Some components commonly found in organic pad are glass, Kevlar, and carbon. Organic pads have what enthusiasts consider a ‘mild’ character. They tend to be softer, easier on rotors, and they don’t make much noise. In the US, most OEM’s ship organic pads in new cars because they don’t require a lot of heat to generate friction, or bite. They are therefore safe for commuting in various environments. While these pads offer comfort, their Achilles Heel is a severely limited temperature range. Once they reach their maximum operating temperature, they almost immediately lose their coefficient of friction and burn up very quickly.
The materials used in these pads are the least costly to acquire, as are the tools and processes to manufacture them. Therefore, organic pads are typically the least expensive pad type.
Not surprisingly, semi-metallic pads get their name from their composition. Each friction puck contains a substantial amount of metal. Common ingredients are steel wool, iron, or copper, mixed with fillers, friction modifiers, and lubricants such as graphite. On the plus side, these pads have higher operating temperatures than organic pads, draw heat out of the rotors, and do not wear as quickly. On the other hand, they’re more abrasive and tend to wear rotors more quickly, make more noise, produce heavier dust, and many times have very little cold bite. Most race pads on the market today are semi-metallic.
Because the constituent materials, tools, and processes involved are more expensive than those used to produce organic pads, semi-metallic pads are more expensive.
The term ‘ceramic’ has been a hot marketing buzzword in brake pads for the past decade. These pads are created by mixing ceramic fibers, fillers, and bonding agents. The greatest benefits of ceramic pads are their lack of dust and noise. They tend to wear a little longer than organic compounds, and are also a bit more rotor-friendly. While they may have a higher temperature threshold than some of the organic compounds, they cannot compete with semi-metallic or sintered pads for heavy duty use. Enthusiasts who spend a disproportionate amount of time staring lovingly at their 6” polished rim lips may enjoy ceramic pads. Those who prefer to actually drive their car hard may be disappointed with the performance of ceramic pads.
While sintered pads have been popular on motorcycles with steel rotors, they remain an emerging technology for automotive use. Most sintered pads are formed from a copper alloy powder. The powdered metal is mixed with other lubricating and wear controlling constituents such as graphite and carbon, formed into the required shape, and then brazed to a backing plate at temperatures as high as 1800 degrees F. ]
Sintered pads have some unique characteristics vs. other pad types. Their nearly pure metal content provides a stable coefficient of friction from cold to hot, meaning they often need almost no warm-up time to produce bite. Since they’re formed at extremely high temps, they don’t fade under extreme use. They also don’t create as much of a transfer layer on rotors, and therefore don’t require a lengthy, traditional bed-in procedure. Since the pads are semi-porous, they can be used in any weather condition: rain, snow, mud, etc.
Because they are mostly metal, the negatives traditionally associated with sintered pads have been increased rotor wear, noise, and the transmission of heat into the calipers.
The materials, tools, and processes involved with producing sintered pads are the most expensive of all current pad types.
The chart below provides a summary of expected pad characteristics based on the material composition. There are exceptions, but these are the general rules of thumb.