Here at HOT BIKE we take what's going on in the motorcycle industry seriously. As part of our top-secret (until now, that is) anecdotal subjective study of the current trends of the two-wheeled variety, we noticed that big is in. "Big" as in large displacement, additional gears, fat tires, wide and high bars, more, more, more. OK, we're just like you-guys riding and wrenching, trying to squeeze every tenth of a horsepower possible for quick launches, bragging rights, and tire-shredding acceleration.
That's great-we love it, you love it, and the industry loves it. But (you knew that was coming) how about slowing down that 1/2-ton bagger loaded-toward-the-sky two-up as the "I didn't see him" cage driver pulls out to ruin your moment of pleasure? Obviously, this is leading toward a story about the opposite of speed; we're talking the oft-overlooked deceleration duties that we should be just as concerned with. Brakes for the American V-Twin have evolved to levels only seen on the racetrack just a short time ago.
Even Harley-Davidson decided to enter the 21st-century world of better braking by equipping all of its bikes (except the Springer models) with a fixed-mount four-piston front brake caliper for the model-year 2000, which replaced the single-piston floating caliper.
OK, before we proceed, a few terms should be loosely defined. The piston (or puck) in the caliper is the cylinder that pushes against the brake pad when activating the brake lever. On the H-D floating single-piston caliper, only one piston on one side of the disc (rotor) is activated by brake-line pressure. As that one outboard-lying piston pushes on its brake pad, the caliper and the opposite brake pad move ("float") as a unit to clamp down on the rotor. It worked but was often overworked due to the small pad area and flex within the caliper and mount. The newest H-D incarnation (also made from cast aluminum) contains four equally sized pistons-two on each side of the rotor. All four of the pistons are hydraulically controlled to squeeze the pads against the rotor. Another big difference from the earlier calipers was that the new brakes were solidly affixed to the fork leg. A much better unit for sure over the previous model, but still prone to flex and heat buildup.
High-performance brake calipers from makers such as Performance Machine (PM) are manufactured from a block of billet aluminum that practically eliminates caliper flex. This means more of the braking energy is transferred to the disc where it belongs. Another significant advantage to PM's calipers is the inclusion of differential-bore pistons within the caliper. What this means is that the pistons on the same side of the caliper are of different diameters. The theory is that the majority of heat buildup in the brake system occurs at the leading edge of the caliper where the spinning rotor enters. Using a smaller piston at this entry point, compared to the exit point, not only reduces heat buildup but also balances out the braking force, leading to better control and feel at the brake lever. An added bonus is more even pad wear and longer pad life due to the equalized pressure being applied across the entire pad.
As the other half of the friction duo to the brake pad, the rotor is an important element in effective braking. Besides the material used, its construction and diameter are important factors in the overall effectiveness of the brake system. Almost the entire current breed of rotors for the V-Twin market is made from different alloys of stainless steel that provide a good balance between friction and aesthetics. Cast-iron rotors may be better from a stopping standpoint, but they rust almost immediately after exposure to environmental elements.
Another design feature inherent to rotors is whether they are fixed or floating in design. The fixed rotor consists of one piece that includes the friction and bolt area used to fasten it to the wheel's hub. A floating rotor is made from two major parts: the inner carrier that attaches to the wheel, and the rotor that is the outer friction ring. The two parts are held together with buttons that permit expansion/movement, due to heat and braking forces, between the rotor and carrier. Just as with the size and number of pistons in the caliper, the diameter of the rotor affects braking power. A larger rotor will stop quicker and stay cooler than a smaller rotor. Excess heat is the enemy of effective braking.
With that brief tutorial taken care of, let's get on to the evaluation. Starting with an '06 H-D Street Glide equipped with the stock dual front 11-1/2-inch discs and calipers, we set about making this bike stop on a dime while looking better doing it. We contacted Performance Machine to install a few of the company's different brake setups. The following photos document the progression in both braking effectiveness and cost.
We in the V-Twin world like to talk about stages when doing motor hop-ups, so we're going to loosely define the three stages of brake systems we installed. Stage 1 upgrades consist of changing out the OEM calipers with PM's differential-bore four-piston unit for '00-and-newer Harleys with a stock 11-1/2-inch disc (Left side: part No. 0053-2919-P; MSRP: $399.95. Right side: part No. 0053-2920-P; MSRP: $399.95). Stage 2 uses six-piston differential-bore calipers (Left side: part No. 0053-2915-P; MSRP: $449.95. Right side: part No. 0053-2916-P; MSRP: $449.95) with the stock rotors. Stage 3 is an all-out performance package that uses six-piston differential-bore calipers (Left side: part No. 0053-2917-P; MSRP: $449.95. Right side: part No. 0053-2918-P; MSRP: $449.95) designed for PM's 13-inch full floating rotor ($399.95 each in 16 different designs to match PM's wheels).