When I heard a year or more ago that some MotoGP teams were adopting carbon-fiber fork legs, my first question was, "Are we talking about the upper outer tube or about the lower inner tube?"

In 1984, Honda produced carbon-fiber upper tubes for its first 500cc V-4 Grand Prix bike, the NSR500. Supposedly costing $40,000 apiece, they looked just like metal tubes as they were externally sleeved with shiny metal to provide a proper friction surface. It was clear at the time why they were trying this: Disc brakes plus slick tires were subjecting forks to increasing bending loads and Honda engineers were looking for a way to handle those loads without having to use more and more heavy steel for the purpose.

Valentino Rossi MotoGP Austin
Fourth quickest overall during Friday practice at Circuit of The Americas, Valentino Rossi used the latest-spec Öhlins carbon-fiber fork legs.Yamaha

Kayaba had dealt with an earlier version of this problem on Yamaha's two-stroke TZ750 by giving its steel uppers a hefty 5mm wall thickness, bringing the weight of the two tubes to a very substantial 10 pounds.

Honda’s solution, expensive as it was, was not widely adopted. In its place, the so-called “upside-down” fork, which places the larger-diameter outer tubes at the top, quickly became the norm. Since the stiffness of tubes increases at something like the fourth power of diameter, putting the larger, outer tubes at the top, where maximum bending moment occurs just under the lower crown, was entirely rational. The upper tubes were now a lathe job, machined from high-strength aluminum tubing. Fitted into the fork crowns, these made a quite rigid and fairly light assembly.

Somewhere along the way, an engineer must have decided to compare the weights of carbon and aluminum outer upper tubes, and the answer was that either a useful amount of weight could be saved—let’s say 1.5 pounds for the two—or the upper tubes could be made substantially stiffer at the same weight.

It was therefore interesting to wait for a Yamaha MotoGP garage tour, scheduled for noon on Friday at Circuit of The Americas near Austin, Texas. As I arrived I saw I could get nowhere near the garage, as a dense crowd of spectators had gathered in hope of a glimpse of their hero forever, number 46, Valentino Rossi. I knew the moment he appeared for a shout went up from all the people, with cries of “We love you!” as 100 smartphones were held high. At no time could anyone actually see Rossi, except for perhaps one woman who was hefted onto a shoulder by a powerfully built fellow in a Scottish kilt. Next came chanting: “Vale, Vale, Vale!”

Sometime after the excitement subsided, we all filed into the garage. “No pictures in the storage area. No video at any time.” Meaningful glances assured anyone in doubt that violators would be towed.

We behaved well and as we walked stared in silence at a bare fuel tank, which is L-shaped as a result of the shift in fuel position from atop the engine to under the rider’s seat. A super-powerful motorcycle such as a MotoGP bike is a dragster with some limited turning ability. As such, the rider has been moved steadily forward, and the fuel has had to be moved out of his way.

A few more steps and we passed two gas recharging units for the pneumatic-valve systems on the engines. We could feel heat as from a campfire, radiating from a zipped-up cabinet full of tires mounted on wheels, ready.

Now we were arranged around one of the number 46 bikes and could see its dark carbon-fiber Öhlins outer upper tubes, and we were told of their weight-saving virtues. Ah, there are wires coming from a non-rotating device affixed to the outer face of the engine’s sprocket shaft. Could this be an example of the torque meters used during practice to measure track friction?

Motorcycle racing is a high-level intelligence operation. While the rider gathers data, continuously analyzing and acting upon it, electronic systems do the same. There on the right-hand fork leg is something familiar to most of us, a linear potentiometer to report suspension position. The computer then converts position change over time to velocity, to rate of acceleration, and to “jerk,” the rate of change of acceleration, essential to good anti-wheelie-system function. Always remember Rossi, all those years ago, saying, “The wheelie is the enemy.”

Maverick Viñales MotoGP
Maverick Viñales, his factory Yamaha sporting the standard gold-anodized aluminum legs, posted the third-best lap time. Andrea Iannone on the factory Suzuki and Repsol Honda' s Marc Marquez were quicker yet.Yamaha

Casting an eye over the bike as a whole reveals what the famed Ducati accessory catalog is: MotoGP-quality parts and assemblies at MotoGP prices. Once you have seen parts at MotoGP level, all else becomes drab.

Our tour guide told us that Maverick Viñales has said of the carbon tubes that they sometimes seem “a bit jittery.” We expect that from structural stiffness. On a big airliner, we see the wings bend almost lazily. But on a little regional jet, wing motion is stiff and choppy.

We learned that the outer upper tubes have metal wear sleeves inside them, with a narrow bushing and seal at the bottom to bear against the very smooth chrome surfaces of the inner lower tubes, and with a second bushing at the top of each inner tube. Assembly must assure concentricity and free motion.

Confident 1970s and ’80s reports of a soon-to-come demise of the telescopic fork were premature. Years of experimentation with supposedly more advanced, Formula 1-inspired alternative front ends have yet to equal the light weight, stiffness, and delicacy of steering of a fully developed telescopic. Its detailed evolution continues.