INTERESTING BRAKE LINE TECH ARTICLE - Sportbike Addicts

bikerguyzx12 · 10-27-2006, 01:06 PM

Brake Line Facts and Fiction
by Paul Wright

So you want to buy some performance brake lines for your motorcycle, but can't decide which is best for you? We understand your delima. There are lots of different brands out there, including Russell, Goodridge, Fastline, Fren tubo, Galfer, and more, plus there are "-2" and "-3" sizes, and you have a choice of stainless steel brake lines, Kevlar brake lines, and even carbon fiber brake lines. How do you choose the right brake lines for your motrorcycle?

I'm going to explain the facts about performance brake lines and explode some of the popular brake line "myths" we often hear, even from experienced racers that should know better. After reading this article, you will know more about motorcycle brake lines than the salesman at your local motorcycle shop, more than your buddies, more than just about anybody. In case you don't want to read the whole article, I will cut to the chase right here and tell you the brake lines you need to buy are made by Fastline, but if you want to know why, you will have to read further!

HOW HYDRAULIC BRAKES WORK

All modern motorcycle brake systems use hydraulics, and the physics behind this is pretty simple: liquids do not compress. Whatever pressure is generated in the master cylinder brake fluid is directly moved through the brake lines into the calipers, pushing the brake pads out against the rotor, creating friction and stopping the motorcycle.

The design of a typical motorcycle front brake master cylinder and lever allows you to generate over 4,000 lbs of pressure within the brake system. That's a lot of pressure, but that's what is needed to stop a spinning brake rotor on a 400 lb motorcycle at speed. Since liquids don't compress, the pressure throughout the brake system is essentially equal at any time. The pressure in the master cylinder is the same pressure as in the caliper, and also in your brake lines. That is why you need good brake lines. They have to convey thousands of pounds of pressure from the master cylinder to the calipers.

BRAKE LINE BREAK DOWN

There are 4 basic parts to a performance motorcycle brake line. The fittings on the end, the teflon inner sleeve, the material around the sleeve that gives it strength, typically braided stainless steel, and usually there is a protective coating on the outside. We are going to take a look at each of these components and explain what works best.

The fittings are either steel or aluminum, and we don't recommend any brake lines with aluminum fittings. Steel fittings are MUCH stronger, are less prone to vibration and stress fatigue failure, they are almost impossible to kink or break in a crash, and they do not deform when you accidentally over tighten them during assembly. Yes, the steel fittings weigh 1 ounce more. You can live with that.

The Teflon inner sleeve is what actually contains the brake fluid, but it does not have enough strength by itself to stand up to the pressures in your brake system.

The material around the inner teflon sleeve is the key to making a performance motorcycle brake line. The material used must be flexible but strong, controlling expansion of the teflon sleeve when pressure is applied to the brake system.

The outer coating is there to protect the brake line (and your motorcycle) from abrasion as the motorcycle moves around and the suspension compresses and extends, causing the brake lines to rub against parts of the motorcycle. Years ago, many brake line brands came without any protective covering, and we saw many brake lines get rubbed nearly to the point of failure. Some brands of brake lines still come with no protective covering, and we definitely do not recommend them.

BRAKE LINE EXPANSION DYNAMICS

When a brake line expands too much under pressure, two things happen that you do not want - loss of internal brake system pressure which means a loss of braking power, and loss of "feel" at the brake lever. Let me give you an easy example. If you had a small round balloon filled with brake fluid, and you squeezed it in your hand, the ballon would expand anywhere it could, and it would feel mushy, and maybe even burst. If you placed the same brake fluid filled balloon in a small bowl the size of the balloon, covered the top completely with the palm of you hand and pushed down to compress the ballon in the bowl, the balloon would feel as hard as if it was solid.

Remember, liquids do not compress, and the balloon can not expand when encased all around by the bowl and your hand. In this example, the balloon is like the teflon sleeve, and it needs something around it to control the expansion when pressure is applied.

CONTROLLING BRAKE LINE EXPANSION

The real trick is controlling the expansion, not eliminating it. If you could totally eliminate brake line expansion using a steel tube from your master cylinder to the caliper, you would have brakes that were so sensitive and grabby that manufacturers would have to re-think brake pad compounds and master cylinder designs. You need a small amount of expansion (about 4%) for motorcycle brakes to have the proper "feel" that is critically important to racers. Too much expansion and you loose braking power and feel, too little expansion and your brakes will be too sensitive to have good control at the lever.

The reality is that most brake lines, even aftermarket "performance" lines, simply have too much expansion. The stock rubber lines that come on most bikes are fiber reinforced, but do not do a wonderful job of controlling expansion, and when they get hot, the rubber become softer, allowing more expansion.

-2 and -3 BRAKE LINES EXPLAINED

I sometimes hear racers claim they like the -2 lines better because they have better feel and braking power. The truth is -2 lines do have a different feel to them , but they do not give you more braking power than -3 lines, and in fact -2 brake lines can cause a serious problem not found in -3 lines (more on that later).

First let me explain that the -2 and -3 terminology simply refers to the inside diameter of the brake line teflon sleeve, -2 being 2mm, and -3 being 3mm. Now if liquids don't compress, and any pressure created in the master cylider is also present in the caliper, how can the diameter of the brake line make any difference in braking power? Good question! Assuming the two brake lines have the same expansion percentage, there is no difference in the pressure deliverered by a 2mm line over a 3mm line, but there is a difference in volume.

Most motorcyle front master cylinders have bore diameters around 14mm. The 2mm line volume is less than half that of a 3mm line, restricting the flow from the master cylinder, making the lever feel "tighter", and giving a different "feel" at the lever. This is why some people like the 2mm brake lines better than 3mm brake lines. Braking power is not increased, but the perception of the braking power does change.

So why are so few brake lines made in the 2mm size? Most manufacturers know what we also discovered years ago with our own race team bikes - the 2mm lines do not flow enough volume to allow a fast retraction of the pads from the rotors. This means that when you release the brake pressure, the extra restriction of a 2mm line keeps your pads rubbing against the rotors far longer than with 3mm brake lines. There is no "return spring" in your calipers. The pads retract only as the fluid flows back out of the caliper, through the brake lines, and back into the master cylinder. Slower pad retraction caused by 2mm brake lines can cause your brakes to stay much hotter, inducing pad glazing, pad backing plate warping, brake fade, premature fluid break down, and even warped rotors in extreme cases. We do not recommend any 2mm brake lines.

THE ANSWER TO THE PROBLEM

If 3mm brake lines have plenty of volume, but 2mm brake lines offer enhanced feel, why don't brake line manufacturers have something in between to give you the volume you need and better feel? The answer is price and profit. The common line sizes available are 2mm and 3mm, so that is what is cheapest and most easily obtained by brake line companies to manufacture their brake lines. We are aware of only one company (FastLine) that specifies and uses the more expensive 2.5mm brake line, and they have it made with the correct weave of braided stainless steel that also gives you the proper expansion rate. How they keep the cost reasonable is a mystery, but FastLines cost about the same or less than other major brands.

THERE ARE OTHER FACTORS TO CONSIDER

While proper brake lines are important to having excellent braking feel and power, there are other factors to consider. An impoperly bled brake system contans air bubbles. While liquids do not compress, gasses do. Essentially any air in your brake system is an internal expansion area, creating the same problems as brake lines that expand too much.

Braking friction generates a lot of heat in the caliper area, and if you don't use a quality high temp brake fluid, you can actually boil the fluid in your brake system. When this happens, some of the the brake fluid becomes a gas, and you have the same problems created by air in the brake system. Change your brake fluid often, especially under racing use. Heat and contaminants in the brake system degrade the fluid over time. The bore diameter of your master cylinder and the leverage ratio it has can make a difference in feel and lever travel. Your brake pads can be slightly warped, or glazed, or just not of good quality. Heat and time in use degrades the brake pad compound. Just because your brake pads are not worn down nearly to the metal backing plate does not mean they don't need replacing. This article is about brake lines, but you can Read More(coming soon) about your other brake components.

BRAKE LINE FAQ's

Q My brakes seem to work OK. Do I really need stainless steel brake lines or any other kind of performance brake lines?

A Do you really need a helmet? Good brakes are important for your safety, just like a good helmet. Better brake lines mean better braking, and that can mean shorter stopping distances, increased 'feel' at the lever, and far less brake fade after repeated hard stops.

Q I'm not a racer, I just ride on the street. Are performance brake lines really going to be a benefit for me?

A Better brakes are better brakes, period. Your safety is important on or off the track, and avoiding a collision with a 5,000 lb SUV on the street is at least as important as avoiding a first turn pile up on the track.

Q Is there an advantage to Kevlar brake lines?

A They may be 1 ounce lighter. You will never notice that, but what we have noticed is too many instances where kevlar lines developed leaks, particularly where the fittings are crimped on at each end, and it has been our experience that kevlar lines are also not nearly as strong as stainless steel lines. We have too often seen kevlar lines pull out of their fittings in a crash that twists the master cylinder around on the handlebar. The truth is that Kevlar may be great in bulletproof vests, but it is basically a woven cloth, and does not control brake line expansion very well. To compensate for this, most Kevlar lines have an extra thick inner teflon sleeve to help control brake line expansion under pressure, and the teflon does not do a great job either. Our many years of experience with brake lines at the track tells us to avoid kevlar lines, and we just cannot recommend them.

Q What about the new carbon fiber brake lines? Do they have an advantage over stainless steel brake lines?

A The carbon fiber lines are new, very expensive, and hard to find for many bikes. Our opinion is that over time they will prove to be like the kevlar lines... 1 ounce lighter than stainless steel, but certainly less durable.

Q OK, so the stainless steel lines are my best choice. Is one brand better than another?

A Probably any braided stainless steel brake lines are going to be better than the stock rubber lines on your motorcycle. However, there are a many grades of braided stainless steel used to make motorcycle brake lines, hence there are many different grades of brake lines. The diameter of the wire, the quantity of wire used, and the weave pattern all make a difference. And don't forget the inside diameter. 2.5mm is ideal. Each brake line company buys the grade they want to use, and the lower grades cost less, so almost every brake line brand out there compromises to balance performance with profit. Fastline is the only company we know that specifies top grade braided stainless line in 2.5mm diameter.

Q What is the deal with the clear or colored plastic coverings on some brake lines?

A The covering is there to protect the brake lines and the motorcycle from abrasion. Motorcycles move around, suspension compresses and extends, and all this movement causes brake lines to rub on parts of your motorcycle. Over time, the rubbing can wear on the brake lines and the parts of your motorcycle touched by the brake lines. We are going to have to give another thumbs up to FastLine, because they don't use a standard plastic covering. FastLines have a thin coating of super tough Hytrel bonded to the outside of the braided stainess steel, so you get superior protection against abrasion, and the shiny black coating of Hytrel lets the pattern of the braiding show through. Very cool looking, and very durable.