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).