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Old Wizard
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Discussion Starter #1
The problem with any discussion about better brakes is agreeing on the criteria for "better." What a factory rider considers to be better will often be a different opinion than a street rider's, for lots of reasons. There many ways to judge a braking system's performance so better brakes may mean improvement in each of several factors but it usually means improvement in a few factors at the sacrifice of others. Here's a few to consider:

Initial Behavior

Depending on your preference (or need) you can have brakes with an initial vague feeling, a strong initial bite, or something in between. My first experience on a 916 encountering a coolant discharge onto my lane where the car in front stopped abruptly convinced me that brake pads optimized for track performance are not the best choice emergency situations in traffic.

High Temperature Performance

Here's an admittedly extreme example. Brembo sells carbon-carbon disc brakes to a few select GP race teams. These ultra-trick carbon brakes out-brake any other brake rotors, and offer advantages such as higher temperature operating range, less rotating weight and unsprung weight. So why not use them on the street? Ignoring their high cost, the main reason is that they take a lot higher operating temp range to work properly. That's why these GP bikes use brake/tire warmers.

Wear Characteristics

On a race bike you can select brake pad and rotor material that will survive a race without needing replacement. On the street, materials need to be more durable and function under less severe braking conditions and more varied weather conditions.

Modulation (Feel, Sensitivity, Control)

When you first ride a new bike, you have an expectation: the harder you pull on the brake lever, the faster you will stop. If you've ever locked-up the brakes on an unfamiliar bike when you've first applied them, was your initial thought that they were great brakes?

A braking system needs to establish the closest linear relationship possible between the force applied to the brake lever and the actual deceleration of the bike. Stopping power is technically easy to achieve, but achieving it along with good proportional braking response is very complex. This, I feel, is the major factor influencing braking quality.

For example, it is of fundamental importance for braking safety and performance that the rider should know, in advance, that a force of 500 grams on the brake lever will give a certain deceleration of the machine, and that a force of 1,000g will result in twice the deceleration, regardless of the conditions (beginning or end of braking, hot or cold, dry or wet).

So, often the advantage of upgrading a braking system is not only greater power. The improvement in proportional response is equally important, as it allows the rider to control and gauge the braking power that's applied, as a function of the conditions of adhesion (grip). This represents a considerable improvement in safety on both road and track.

I'll give you an example: The Brembo radial pump master cylinder takes less lever force than the stock unit to produce the same force on the pads, and it also takes less lever movement. Some riders think that this means that they have "better" brakes, but they don't. They have the same braking power with poorer modulation characteristics. Good for the track perhaps, but often dangerous on the street.

Stopping Power and Fade

A braking system must be able to dissipate, in heat, the kinetic energy of the motorcycle (proportional to it's total mass and speed squared). Therefore, the heavier and faster the bike is traveling, the greater its energy and, during the braking phase, the more energy that will be needed to be dissipated very quickly. So the discs and pads, by absorbing a considerable amount of heat, will often reach red-hot temperatures under repeated braking from high speeds. This heat is then removed by convection cooling to the airstream. The temperatures that the brake components reach is a function of the mass of the components, the bike’s speed and deceleration rate and the number of brake applications.

The way that kinetic energy is converted to heat is from the friction forces developed by forcing the pad material and the disc material together. The amount of friction, and consequently the efficiency at which kinetic energy is converted into heat, is also dependent upon the coefficient of friction between the two materials. The greater the coefficient of friction that exists between the pads and discs, the greater the stopping power (frictional forces.)

You can improve braking by using materials that have higher coefficients of friction. Cast iron discs, for example, have a higher coefficient of friction than stainless steel. But there's more to it. The coefficient of friction changes, and when it decreases, it takes more force on the brake lever to maintain the same deceleration so the brakes "fade." The ideal solution is to have a reserve of braking power so that in all situations, the system is consistent and never reaches its limits.

But with actual braking systems there are other things to consider:

• Under light braking with dry surfaces and low pad-to-disc pressures, the friction force is directly proportional to the pressure between the surfaces.*For low surface pressures the coefficient of friction is independent of surface area.

• At low disc velocities the coefficient of friction (and the braking force) is independent of the relative surface velocity.

• At higher disc velocities the coefficient of friction decreases.

• As the applied force to the brake pad rises, the coefficient of friction rises slightly.

• As the disc slows to a stop under a constant braking force, the sliding coefficient of friction quickly rises to a much higher static coefficient value and the rotor can lock if the force on the lever isn't reduced.

Vendors sell brake pads with material formulations designed to behave differently at different velocities and temperatures. Different initial bite, wet performance and fade characteristics, for example.

You can also increase stopping power by increasing the distance between the caliper/disk and the hub. For the same force application, the moment (force times distance) about the axle is increased.

Fade also occurs when caliper temperatures reach a high enough level to cause the brake fluid to boil and the resulting compressible vapor bubbles limit the hydraulic pressure and consequently caliper piston force.

Rider Preference and Adaptation

This is impossible to quantify because it's really the trade-off and balance between some of the above factors. A rider is able to compensate for one performance drawback to gain an advantage with another. But again, it's situational dependent; a braking system that gives repeated stops from 150mph with the force application of one finger is not necessarily optimum for a 40mph panic stop in traffic. Even though a rider is adaptive to a braking system's general behavior doesn't mean that in an emergency that he'll use a light one-finger pull to stop.
 

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Premium Member
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427 Posts
Well... that pretty much sums up what happened to me... the las bit about no problem stopping it in "no-panic mode" and then grabbing just a bit too much at 20mph in panic mode!
I need some advice on pad types that might be better on the street... I don't do track days... too far and too much to lose for me.
 
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