A motorcycle’s steering-head bearings are at the extreme upper front of the frame. Through them passes the steering stem, the shaft that joins the upper and lower fork crowns. And through holes in those crowns pass the upper fork legs of a telescopic fork. The front wheel, its brake equipment, the fork tubes, and crowns all pivot on two rolling bearings in the steering head. Through them pass all the forces of front-wheel braking and steering. Those bearings must transmit without stick/slip or excess friction the messages of the front tire to the rider.
Steering-head bearings can become damaged, dented by a crash or by repeated violent wheelies. They can become rusted if rain or wash water enters the steering head and remains there. The rider will feel the bump, bump as the bearing balls or rollers pass over the damaged areas of the bearing races.
Back in the late 1960s, a somewhat timid young man bought a small motorcycle from Boston Cycles and rode off to high adventure. After some weeks, he returned, saying, “Something’s wrong with my steering.” The service manager put the bike on its stand, sat back to lift the front wheel, and turned the bars.
“Yup, your steering races are dented. The parts are cheap, and the work takes a few minutes. Come back tomorrow.”
When the young man returned, the newly smooth steering was demonstrated to him, and he paid his bill.
“How did this happen? I mean, I don’t want it to happen again.”
The service manager, smiling at his private joke, replied, “You’ve been steering too much.”
The customer carefully putt-putted away down the lane from the service area.
During the 1980s, there was breathless expectation that, any day now, a radical substitute for the motorcycle’s pivoted telescopic fork front suspension would sweep away the errors of the past. Into history’s recycling bin would go the sliding “stiction” of the telescopic legs, the pro-dive braking behavior caused by the angling of those legs, and the structural inefficiency of feeding front tire loads all the way up the fork to the steering-head bearings, then back down through frame members into the rest of the machine.
The best-funded work of this kind carried the ELF name (a French gasoline company) and later, substantial Honda backing. It built one beautifully executed prototype after another, starting with a Yamaha TZ750-powered machine and progressing through a series of 500cc Grand Prix bikes powered by state-of-the-art Honda engines. The strange thing was that as the design evolved in response to the stopwatch and comments of top riders, it moved away from the original complexity, back toward simplicity. Riders found that communication with the front tire was muddled in passing through a multitude of ball joints and levers. Deprived of that information—like Casey Stoner on the super-stiff 2009 Ducati carbon-fiber MotoGP chassis—they had a choice of either going slower or of losing the front without warning.
True believers proposed that as soon as tire manufacturers were producing tires specialized for the new front ends, and as soon as a fresh generation of riders learned to ride the alternative designs, their rational superiority would appear. That is how 1977–1981 National Highway Traffic Safety Administration (NHTSA) bureaucrat Joan Claybrook proposed that her organization’s supposedly safer “backward” motorcycle—steering was by the rear wheel only—would become rideable. No one at the time was able to ride it; their reflexes had all been “contaminated” by knowing how to ride a bicycle or motorcycle.
To this day, the more credulous of commentators refer to radical linkage front ends as “high tech” even though in actual top-level competition they were unable to demonstrate superiority over conventional pivoted forks. That continues to be the case in all disciplines of motorcycle competition, on road and off.
So there it remains: The simple pair of ball or tapered-roller bearings, spaced about 5 inches apart in the steering head, on which the front end so easily pivots. Because said bearings present only rolling friction, the rider is quite directly connected to the tire forces whose messages reveal so much about what the front tire is doing.
Yes, the negatives remain. The telescopic fork continues to suffer some stiction, even though now much reduced by ultra-smooth fork-leg coatings and low-friction bushings. The telescopic fork is still pro-dive during braking because of its rake angle, but dive also lowers the machine-and-rider center of gravity, enabling harder braking before rear-wheel lift sets the limit. And when you steer through a telescopic fork, you do have to rotate the extra mass of the fork legs, not just the wheel itself as in a hub-steerer. But fork tube weight has been considerably reduced by adoption of larger but thinner-walled lower tubes and by carbon-fiber upper tubes in MotoGP.
Engineering can’t make everything perfect because nature forces compromise on us. We could look upon the metal turbine blades of fan-jet engines as a joke because their low melting point requires the hot combustion gas to be diluted with pure air to a temperature they can survive, albeit with laser-drilled air holes that sheathe the hollow blade in a thin layer of cooling air, for this increases fuel consumption. Why not toss metal blades away in favor of ceramics that just giggle at temperatures that melt tungsten and rhenium? Because more than 50 years of ceramic development failed to come up with alternatives as reliably strong as metal blades. Only quite recently has there been real progress in this area.
So engineering can’t drop everything to seek perfection. It seeks the best practicable solution at a given time, that represents workable value for money.
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