The Earles fork was a variety of leading link fork where the pivot point was aft of the rear of the front wheel this was the basis of a patent for the design. Designed by Englishman Ernest Richard George Earles, this triangulated fork actually caused the front end of a motorcycle to rise when braking hard the reverse of the action of a telescopic fork. It was designed to accommodate sidecars, and from 1955 to 1969, BMW used the fork even though most of its motorcycles were sold as solo bikes.
See Earles' 1951 patent application at the bottom of this page.
Perhaps the greatest benefit of the Earles fork in sidecar use was its adjustability for rake and trail. The swinging arm pivot had two positions. Moving it to the forward position reduced trail, allowing the bike to turn with less effort when a sidecar was attached.
The photos below shows the Earles fork as used by a British company, Douglas motorcycles, on its 1950s vintage, opposed-twin, 348cc Dragonfly model, two of only 1,600 built. Notice that this Earles fork has only one swing-arm pivot point, unlike BMW's forks, so it was intended only for solo usage, and was not adjustable for sidecar use.
The motorcycle manufacturer that produced the most Earles-fork equipped motorcycles clearly was Munich-based BMW. Ironically, in 1935 it was the first manufacturer to produce oil-dampened telescopic forks, on the R12, which it then abandoned for the Earles fork. The latter fork was most useful in sidecar-equipped motorcycles, but the vast majority of BMW's Earles fork bikes were sold as solo machines.
From the 1956 through the 1969 model years, most of its motorcycles both twins and singles came with Earles forks. These models included the R26, R50, R60, R69, R27, R50/2, R50S, R60/2, and R69S.
Above: A BMW R60/2 on the left, and an R69S on the right, both with Earles forks. Note that the swinging arms are mounted in the rear pivot points, which is appropriate for solo motorcycles. For sidecar use the swing arm is moved to the forward pivot point (other changes would be required as well, such as different rear drive gears, a different speedometer ratio, and stiffer suspension units).
Above: A factory diagram of the R69S Earles fork from the 1966 BMW Instruction Manual on the left and an original blue R50/2 on the right. Click on the diagram to read “Technical Data” pages from the 1967 owners manual
Below: Where is the world's only Earles Fork Road? It is the home of Bench Mark Works, founded by Craig Vech Vechorik, which supplies parts for vintage BMW riders all over the world. This noted road is in Sturgis, Mississippi, southwest of Starkville:
The sign below was placed in 2013 at the entrance to my driveway by my good friends Jim and Denise Strang. It was an amazing birthday surprise!
Right: With the R1100RS in 1993, BMW introduced on its boxer twins the Telelever fork, a variant of the British Saxon-Motodd design, wherein an additional swingarm that mounts to the frame and supports the spring. This causes the trail and castor angle (rake) to increase during braking instead of decreasing as with traditional telescopic forks. The two fork sliders have no damping, as a central coilover hydraulic damper, supported by an A-frame connected to the engine crankcase, handles that.
As with the Earles fork, this fork can eliminate dive during braking if it is tuned to do so. However, BMW tunes in minimal dive under hard braking because riders are used to that with telescopic forks.
On December 5, 1951, Ernest Richard George Earles applied for a patent on "Motor Cycle Front Wheel Forks." Below are copies of his four-page patent application for the forks, now known as Earles Forks. The first image below is page four of the patent application, which is Earles' own diagram of his concept. Click on the second image below, which are the pages of his application, to see the full patent application in a PDF file.
The fork of the Russian Ural motorcycle, seen to the right, is a leading link fork, not an Earles fork, and is installed on many Ural sidecar-equipped motorcycles.
As noted above, in an Earles fork the pivot point is aft of the rear of the front wheel that was the basis of a patent for the design. The pivot point of the leading link fork is forward of the rear of the tire.
Another leading-link fork is the ExtensoDive fork by EML Engineering in Holland.