Faltenbalge

BMW was an early innovator of the oil dampened telescopic front fork, which is well documented.  While I have seen claims that BMW was the first to use them on the R12 and R17 in 1935, in fact oil dampened telescopic front forks appeared one year earlier on the Danish built Nimbus produced by the firm Fisker & Nielsen.
 
Of course the production road models before the war used metal shrouds or housings to conceal the inner workings. This practice continued in the early post war years on the twins including the R51/2 and R68.   In late 1952 after the production of the first 300 or so R68's had rolled off the assembly line, a modification was made when the use of rubber gaiters on the front forks became standard.  This was the practice until 1955 when the R50 and R60 were introduced with the Earles fork front end. 

The front gaiter was reintroduced by BMW on the R60US and R69US just prior to the major redesign and introduction of the /5 series.

Of historical note, and particular interest to people like me who dwell in minutia, is the clever use of rubber gaiters on an Earles fork equipped bike as show here, piloted by Anke-Eve Goldmann. (Photo from thevintagent)

For those interested there is a fantastic article on the history of BMW forks in
BMW Motorcycle Magazine, issue No. 5.  Unfortunately they are sold out of back issues, so borrow a copy from a friend!

Despite the switch to rubber gaiters up front, the rear springs remained clad with metal cans.  Those wanting to shave a little weight from the rear suspension instead cover the rear springs with rubber gaiters or "faltenbalge" in place of the metal cans.  The use of gaiters requiring an aluminum ring at the top and bottom of the rear spring over which the lip of the gaiter is stretched.  The gaiters were then held in place by means of a 9 mm wide special ratcheting clamp.




Rear view demonstrating the aluminum rings at the top and bottom of the left rear suspension spring.  On the right, the "faltenbalge" in in place.

 

The aluminum rings and rubber gaiters were available through Schorsch Meier's parts catalogue.  Whether or not other purveyors of aftermarket "teile und zubehör" such as Ernst Hoske had them available, I do not know.

The top and bottom ring are on the left and right, respectively.

While the aluminum  rings aren't currently available, the rubber gaiters are easy to source from any British motorcycle parts supplier.  The Triumph/BSA part number is 97-1645.  If there is enough interest, I would consider having the aluminum rings reproduced. 

If/when I have time, I'll weigh the components of the rubber gaiter setup vs the original metal cans, and see if there is, in fact, any weight savings.  I, suspect there isn't, and there could even be a small weight penalty.  But you can't argue with cool!