Braking System - Perspectives

Stopped Cold
In a better world, the performance of brakes and engines would be more closely matched than has historically been the case. I came to motorcycling at a time when braking power and horsepower were in rough parity, at least in the context of the average rider's demands. The same could not be said of the cars I'd been test driving. My driving style made the inadequacies of passenger cars' brakes especially obvious, and I suggested that we add a braking phase to our testing of vehicles. Nothing complicated: a single maximum-effort stop from 80 miles per hour, the highest speed limit on interstate highways at the time.

American cars found my 80-0 mph braking test hopelessly difficult. The little "rope-drive" Pontiac locked first one wheel and then another, before diving off on the road's dirt shoulder. The worst of this lot was Studebaker's "Golden Hawk," which would have been better named the "Cast-Iron Turkey." When I applied the Studebaker's brakes, hard, the car first swerved unpredictably, then straightened as its brakes began to fade. By the time I had it slowed to 35 mph its brakes had faded totally away, both of my feet pressing the brake pedal while the car coasted freely down the road.

Motorcycles, being single-track vehicles, are not made to swerve by uneven braking, though a front wheel lockup can cause a sideways swerve just before the motorcycle hits the pavement. Such lockups were exceedingly rare events in motorcycling's first 50 years. Most bikes made before 1920 had no front brake of any kind; those that did had bicycle-style calipers clamping the front rim, with feeble effect.

When motorcycles got drum brakes on their front wheels they were only a little less feeble than the rim clamps. There's not much you can do with a five-inch drum, and the manufacturers accepted the inevitable without embarrassing themselves in an unseemly struggle. The makers of motorcycles with bigger brakes did nothing but increase their diameter-up to eight inches. They retained the single-leading shoe design, said shoe being pivoted at its trailing end so that the shoe's leading end wedged itself into harder contact with the drum.

It was a trivial matter, mechanically, to have both of a drum brake's shoes leading, but this was done only rarely until the disc brake was just over the time horizon. This change occurred not in anticipation of the disc's arrival; it was a matter of road performance beginning to overwhelm braking performance. The transition is brought on suddenly by the fact that kinetic energy (which brakes convert into heat) rises as the square of speed. This unquestionably accounts for the double leading shoe front brake on Kawasaki's rocket-like 500cc triple.

Disc brakes, when they appeared, seemed magic. But the best, most controllable front brake I used in my racing days was a double leading shoe Italian Oldani fitted on my Harley-Davidson Aermacchi. No disc brake would have been better, because it wouldn't have been more controllable, and the Oldani drum brake was sufficiently powerful for the purpose.

In sharp contrast, one of the most diabolical brakes in my experience was on an early disc-braked Kawasaki. This little beauty was grabby when the lever was first applied, then was oddly unresponsive to further squeezing of the lever-up to a point, beyond which it again became extremely touchy and would lock and dump you on your ear if you weren't careful.

A reader alerted me to an equally diabolical failing of Honda's GL1000, calling to say he had been forced to make a detour down into the center median strip on a four-lane highway one rainy morning. It was that or bunting a big 18-wheeler up the tail because the bike's brakes simply didn't work when wet. I was dubious about the reader's tale because it didn't sound like the kind of mistake Honda would make. Nevertheless, it had to be checked so I rolled out a GL1000 we were testing, hosed down the front brake, and told the test rider on the bike to give it the old college try.

To my immense surprise, the Honda's front brake did nothing at all for a long moment. Then the brake pads scrubbed the water off the disks, and brake effectiveness was restored. I don't know how the brakes would have behaved in a steady rain. Steady rain is a rare commodity in Southern California, so very few test bikes were ridden in the wet.

I think the wet-road problem encountered by some of the early disc brakes was caused by the use of brightly polished discs. I don't hear any complaints about the newest brakes, with their surface-ground, satin-finish discs-the latest development in our ever-evolving brake systems.

I invite readers' comments, suggestions and even criticisms. My e-mail address is gj@ wheelbase.com; call me at (805) 239-2192, 9:00 a.m. to 5:00 p.m. PST, or fax (805) 239-0855.