About 35 years ago, the telescopic fork came under vigorous attack from a variety of alternatives—ELF/Honda's hub-steerer and MacPherson strut, Bimota's hub-pivot Tesi, and the strut forks of John Britten, Claude Fior, and Norman Hossack. True believers in the alternatives persist to this day in their certainty that the stiction and pro-dive aspects of "teles" will yet be their downfall. They also are apparently sure that more parts equal more performance.

Yet four or five decades before that, telescopics represented the radical leading edge over existing short-travel front ends such as Britain's once-dominant girders, Indian's short trailing link, and Harley-Davidson's short leading-link springer, once known and revered in Britain as the "Castle" fork. For a time, the telescopic vied with BMW's postwar long leading link and Guzzi's shorter, stiffer variant. How short was short travel? How about an inch to an inch and a half?

1919 Harley-Davidson Sport twin
Springer evolution: The 1919 Harley-Davidson Sport twin represented The Motor Company’s first use of an external fork spring.Harley-Davidson

In 1935, the long reign of rigid rear ends for racing motorcycles ended when Stanley Woods won the Senior TT on a Moto Guzzi 500 with rear suspension. At Velocette in England, racing engineer Harold Willis saw it was time for change. Willis, a private pilot, was friends with George Dowty of Aircraft Components Co. Dowty had through sheer persistence introduced to aviation the oleo strut—a telescopic suspension unit combining hydraulic damping with use of compressed air as a springing medium. Dowty had earlier fought his way through the conservatism of giant rubber bands, leather straps, and other contrivances that had been used to support aircraft during taxiing and to absorb the impact of landing. Dowty, for a time a part of Messier-Bugatti, is now an element in the world’s largest manufacturer of aircraft landing gear, Safran.

According to research performed by Dennis Quinlan, Willis arranged with Dowty to have six sets of oleo legs made up in a size suitable for a motorcycle. Those, and a fork based on the same technology, would inspire Velocette’s new suspension.

Norton, too, saw it was time for something better than girders, but its first step was a simple but longer-stroke telescopic whose only damping was the grease with which it was assembled. BMW, whose primary product at the time was aircraft engines, were the first to put hydraulically damped telescopic forks on production models, the R12 and R37 of 1935. BMW's aviation activities were transferred to MTU in the post-WWII period.

Ducati 904cc 851-powered Tesi 1D SRs
Bimota made fewer than 150 of its Ducati 904cc 851-powered Tesi 1D SRs.Michael Hintz-Madsen

Telescopic forks had been tried many times prior to 1935 by other firms but the idea had not been widely adopted. Showa, the large Japanese maker of motorcycle suspension, was organized in 1938 to produce aircraft components.

When WWII ended in August 1945, US wartime industries scanned the industrial horizon for ways to remain in business. Grumman, who had produced thousands of aircraft for the US Navy, turned to stretch-forming aluminum canoes. The Vard Corporation, delivering thousands of sets of aircraft landing gear, decided to apply its sealing, damping, and cylindrical grinding technologies to making a hydraulic-damped telescopic fork for Harley-Davidson big twins. Price was $70 a set, and the fork was supposedly inspired by BMW’s previous work.

forward-retracting nose landing gear
France’s Safran produces this forward-retracting nose landing gear for the Airbus A380 double-decker airliner.Safran

Supposedly the US firm Menasco, which also had produced vast numbers of aircraft landing-gear sets, either consulted with or supplied parts for Harley-Davidson’s 1949 conversion to telescopic forks. The resulting model took the name Hydra-Glide. When rear suspension was later added, the name became Duo-Glide.

Racing led the way to telescopics mainly because the appearance of 8-inch-and-larger front drum brakes in the 1930s produced deceleration forces that bottomed short-travel alternatives. A suspension’s ability to absorb energy is proportional to the square of its travel, making the relationship a powerful one: Double the travel and you can absorb four times the energy. On production bikes, the longer travel of telescopics was a key to improved road-holding and comfort. In the various forms of leading- and trailing-link forks, an important drawback was lack of stiffness to prevent road forces from tilting the front wheel out of plane with the rear wheel.

Once the basics of hydraulic damping, sealing, and production of truly straight tubes (often wear-protected by chrome or other hard surface) were widely understood, motorcycle fork building could separate from its aviation origins.