ASK KEVIN: An Earles Fork? Not!

Greeves motorcycle front wheel

QUESTION: Please let Technical Editor Kevin Cameron do more technical editing. I'm sure he would have corrected the erroneous labeling of the Greeves leading-link fork in "Motocross Memories" (July) as an "Earles" fork. The Earles patent of 1953 specifies a link pivot behind the wheel, which clearly is not the case with the Greeves. BMW and MV Agusta licensed the Earles design, but Greeves did not.

Michael Moore

San Francisco, CA

ANSWER: People have gotten into the habit of calling any leading-link motorcycle fork an Earles fork. It is clear, as our correspondent points out, that in section 35 of his patent Earles specified a link pivot behind the wheel. Best therefore to use the generic "leading-link fork."

Many leading-link forks have been used. Among them, those used on some postwar BMWs (pivot behind the wheel), 1950s Moto Guzzi GP bikes (short links), and on Honda's first Isle of Man TT entry, the 125 twin of 1959 (also short links). The weakness of all such forks is the difficulty of providing adequate resistance to side-to-side tilting of the front wheel. The usual attempt was to either put the pivot behind the wheel as Earles did, in effect using a forward-pointing swingarm, or, if the links were short, to continue the links rearward to form a U-shape behind the tire. This U-shaped affair can be seen in the photo above.

The English have always had a thing about constant wheelbase, as seen in the patent. Hmm, let’s check to see what kind of fork is used in World Superbike, MotoGP, British Superbike, etc. Oh, my, the use of the telescopic fork appears universal, even though such forks are notorious for wheelbase change.

In the later 1940s and early 1950s, there was justifiable dislike of telescopic forks in certain circles, mainly because of their flexibility and lack of stiffness. Gilera went so far as to make for their four-cylinder racers a single steel weldment of upper and lower steering crowns to more strongly hold the two fork tubes parallel under stress. Anyone who has familiarity with British teles of the 1950s and even ’60s knows that you can hold the front wheel between your knees and turn the handlebars a considerable distance either way—and when you release the bars, much of this deflection will remain!

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