Wednesday, June 20, 2007
Hardware: Supermoto Brakes Explained
In the dirt, off-road bikes generally don't need much in the way of brake upgrades. Or if you're like me, where braking in the dirt means just falling off the bike, who needs brakes? The fastest MX bikes in the business will rarely have any real upgrade parts beyond something like a wave rotor, sticky pads and a brake line. But take that same bike and give it seventeens and road-rubber and the rules start to change real fast.
First, a bike that was built by the OEM to have more use out of the rear brake system is reversed, with greater braking power needed right up front for precise steering and maximum stopping power. Now, that little single or dual piston caliper and 220mm vented brake rotor up front just won't cut it.
A look at a complete supermoto brakes system can be broken down into the various parts of the brake system and in order of importance:
Supermoto Brake Rotor
Supermoto Brake Caliper
Supermoto Brake Rotors. The stock rotors on most OEM MX bikes are low end, heavy stainless steel products mostly stamped out in Taiwan for the oems. Since your supermoto is going to be relying on the front brake for most of its stopping power, the rotor size needs to be increased both in overall diameter and thickness. This larger rotor is there to give a greater contact patch for the caliper and pads and dissipate heat quicker, giving you consistent stopping power all through your race or ride. Virtually all except one of the aftermarket Supermoto rotors made uses a wave or wavelike design at the outer ring of the rotor to simultaneously cool quicker and grab more. Motomaster, Brembo, Braking, EBC, use a wave like design with Bering er being the exception, which uses a solid smoothed iron rotor.
All of the upgrade supermoto brake rotors available are a full-floating design. This means that the outer rings are loosely connected rather than solidly with rotor buttons, allowing both to self-center in the caliper, reduce drag and stay cooler.
Upgrading your bike's front rotor is the first step in a supermoto brake upgrade. For street duty, it's common to just stop there and this is perfectly fine for most types of street riding. If you're going to use your stock caliper with a 320mm rotor, you'll need an adaptor to accommodate the now much larger rotor. Motomaster and EBC both offer great street "kits", a rotor and adaptor, that provide the right rotor and caliper relocator bracket to mount up to your wheel and caliper with no spacing issues. The street kits will perform fine for most types of sportsman or non-pro racing duty as well. Just realize that towards the end of the race your brakes will start to fade as they heat up and lose power. Still, if you're used to the little MX rotor on your bike, you'll notice a lot more stopping power on your SM bike with a new 320mm rotor installed.
As a side note- once you get this rotor installed on your bike, you'll notice that removing and installing your front wheel just got a lot harder. If you happen to be running a 16.5 inch front rim on your bike, depending on the caliper you have, clearance will be an issue and more time will be needed to angel your wheel in place without scuffing up your rim. Same goes for the rear for that matter and it's one of those things you'll need to live with if you're going to live with Supermoto, though some caliper makers (namely Motomaster) have designed their calipers to compensate for this less clearance by making a caliper design that is more compact.
Brake Pads. With your new rotor bolted up, along with that relocator, your next order of business should be Brake pads. A simple and comparatively inexpensive upgrade, you'll want to look at and test out a few kinds of sintered or HH brake pads. These pads give higher rates of friction and depending on which rotor you go with will have varying results. We recommend testing out 2 or 3 types of pads to compare the feel of each. Changing out your brake pads after a ride or two is quick and easy and doing this comparison research will give you the ability to set your bike up with the right amount of feel and power.
Brake Line. Another low cost upgrade involves your brake line. Your stock brake line is really a reinforced hose that wasn't designed for much use in the front. This hose will expand during heavy use and will noticeably rob braking power away. The solution is to get a stainless steel braided line, which is essentially a hose wrapped in braided stainless steel to create a barrier from expanding under the pressure of your hydraulic brake system.
Calipers. For the average street rider, or low budget racer, this is where most riders stop in a brake system upgrade. If you want real brakes, the next part to look at is going to be your brake caliper, the clamp that bites down on that rotor and will do a lot of the work of slowing your bike down. Your stock caliper, again, is a light duty deal that was designed for the most part to be used in conjunction with your rear brake once in a while. They're generally made out of cast aluminum with 2 small pistons inside and don't dissipate heat very well at all.
Upgraded supermoto calipers are typically a 4 piston design, with 4 large pistons clamping down on those brake pads all at the same time. Calipers like Motomaster or Brembo are generally CNC machined for weight savings and better at heat distribution, and they're easier to clean. Beringer is one of the few brake companies offering a 6 piston brake system for supermoto. Beringer is also a pioneer in this because they're calipers are all designed as solid unit, rather than a modular caliper and bracket design. Most calipers, Motomaster and Brembo included use a single caliper design, with the actual mounting points designed as a bracket. I don't know of there's any real structural advantage to this, but we assume that the modular design creates more stress on the individual parts, not to mention, more opportunity to have something improperly torqued during installation. Nevertheless, we feel that the Motomaster system really offers the best bang for the buck, in a tried and tested system, with easy parts availability and excellent stopping power. Brembo brakes, on the other hand is one of the few companies to follow the lead of modern sport bikes by implementing a radial mount design, giving the brake caliper a more solid mounting set-up to the fork.
Master Cylinder. Like the rest of your MX bike's brake system, your master cylinder just wasn't designed for the high stress, as well as increased fluid volume needed of your brake system. A hydraulic master cylinder is really a sealed pump that pushes down air-tight fluid through your line with pressure to move and release your calipers pistons onto the pad. Your larger pistons now could use some extra pressure getting them to stop that greater mass and the whole thing needs to act more efficiently and cooler. Your stock master cylinder will actually work in a pinch on most calipers. The Braking caliper for instance basically requires a new master cylinder or almost no pressure will come to the caliper.
The makers of upgraded master cylinders all come to the table with pretty much the same intent. Better materials used than stock, larger fluid capacity, better feel on the lever, lighter weight. Magura, Brembo and Beringer offer high end master cylinders in the 13 to 16mm range for Supermoto. Anything larger than 16mm is really not going to be applicable to your supermoto. 20mm master cylinders are designed for streetbikes using two 4 piston calipers up front. Your bike is nearly half the weight and has half the pistons in the brake system. Brembo and Magura are the most commonly used, with Beringer and ISR really kicking it up a notch with a more compact system.
Fluid. You'll need to invest in some high quality DOT 4 or even DOT 5 brake fluid for your new brake system. We recommend Motul RBF600. It has a high boiling point and cools quickly. It's very important to keep your brake system as cool as possible, since heat is really the enemy of a brake system and the fluid in your brake lines will literally boil if all the parts aren't working correctly.
The above outlines the main points for upgrading your MX bike to Supermoto Race or street duty. Note, that it is very rare that you'll need to do much with your rear brake system. Your rear brake is going to be used a lot less than the parts were designed for. You'll use the back break to assist with backing in and very hard braking. There are no real supermoto specific caliper upgrades and the most you'll want to look at here is a rear brake rotor and better compound pads.