Radial Brakes, Heat Stress, and Code Breaking Questions | Ask the Pro


Radial Brakes
It's been a while since I've owned a bike and I haven't kept up on all the advances. I know this isn't brand-new technology, so here's the bonehead question: What are radial brakes, and what are the advantages? I'm sure the answer to the latter part of that question will stir up the hornets nest at Buell again.
Anthony Hoehn
Canal Winchester, OH

First, thanks for the question. There are a few different caliper styles: floating calipers, fixed calipers, open and closed calipers, monoblock (from billet) calipers and calipers with one or two bridges. But radial-mount systems are, as far as we know, the best. The advantage, compared to any perpendicular mounting system, is better rigidity. Pad pressure on the disc is more evenly distributed, which minimizes the pad taper that tends to occur between the entry and exit pistons. Properly engineered piston sizes further diminish pad taper. The leading piston is always smaller than the trailing piston.

Most race teams now run radially located calipers, and factories such as Suzuki and Yamaha have chosen radial calipers based on racing results. Rigidity and accurate alignment relative to the rotor can translate to an amazing amount of clamping force. The upper and lower radial mounts allow very little flex, preventing the leading edge of the pad from distorting the caliper and com-promising braking efficiency. Most race calipers are machined from one piece (billet) of aluminum to further prevent caliper flex. Even with the two-piece radial calipers found on most production bikes, braking efficiency is exceptional.

Moving upstream, the idea behind a radial master cylinder is to optimize the force generated by our fingers. When we pull on a lever activating a conventional master cylinder, clamping force is transferred, and then turned on a pivot that re-directs it to a piston just to the left. When we squeeze the brake lever connected to a radial master cylinder, the force generated by our fingers works in the same plane as the piston, and isn't re-directed. That direct force application translates into more power and more efficient braking with less lever pressure and increased feel. Another thing I enjoy in some new radial master cylinders is an integral bleeder nipple that makes bleeding brake lines easier.

Heat Stress
Although originally from Southern California, I've called Japan home for about 10 years. It's hard to find Motorcyclist over here, so I usually have to get my brother to send me issues when he has the time (and magnanimity) to do so. I ride a '99 Yamaha XJR1300, which isn't sold in the States, but I don't know where else to turn for expert advice.

The "Pekke Jr."-that's what people call it over here-is a heck of a fun bike. But that big engine is air-cooled, and in the summer it gets incredibly hot, especially in stop-and-go city traffic, so I worry about it overheating. What can I do to cool things down other than going all-out and mounting a larger oil cooler? Would it help if I installed colder plugs in the summer months?
Chris Whitney
Osaka, Japan

The consensus of our office straw poll is this: Don't worry, be happy. The old FJ1200-great-grand-pappy of Pekke Jr.-could get hot enough to soften its piston domes if you headed into the mountains with a hot hand and a heavy load, but such limitations are ancient history. Just make sure your oil cooler isn't mucked up with bugs. But if you insist on stressing, cut the oil-change interval in half and use a first-rate synthetic such as Motul, Motorex or Repsol. Expensive? Peace-of-mind usually is. Aside from optimizing your fuel mixture and ignition timing to beat the heat, which can generate a whole new set of tribulations, AMA Super-bike crew chief emeritus Jim Leonard recommends a strict diet of synthetic oil and super-unleaded. You could add another oil cooler, or even rig a fan, but if you're asking us, just chill.

The Milwaukee Code
Could someone tell me what the letters "FLSTN" stand for?Steve
Via the Internet

Sure. F is for Big Twin. L is for Fat front tire and touring fork. ST is for Softail, N is for Nostalgia. And D is for Done.

There's no such thing as a bonehead question except to the bonehead who can't answer it. So we asked someone who could: Sandro Milesi, Chief Operating Officer at Galfer USA in Oxnard, California. The Milesi family has been coming up with better ways to slow down since Sandro's granddad, Maffio, set up shop in Barcelona 61 years ago. After dealing six decades worth, these guys know a few things about brakes.
Pekke Jr.? Was there ever a Pekke Sr.?