International Six Day Trail (ISDT), now known as International Six Day Enduro, is one of the oldest motorcycling events, and consists of country teams competing in a number of off and on road stages for six days. During the event, only the rider can carry out any repairs or servicing on his bike, and points are deducted for any parts used. This means that the event is not only a trial of the rider's skill and endurance, but also the design and build quality of the machines.
Looking on the Web I found some videos of events from the 50s and 60s that illustrate how hard (and muddy!) these events are, and also how the bikes have developed.
Firstly, a report on the 1956 event held in West Germany. This film was made by the Czechoslovak Government, so heavily features their riders.
No, I've no idea why there are some people at the start wearing rather bogus 'Scottish Highland Dress'!
Surprising to see how many of the bikes look like standard road models, and also how small some of the bikes were. This Italian rider is on a 75cc Capriolo.
Now onto the ISDT featured in the Facebook posting, 1965 in the Isle of Man. The video is split into 3 parts:
See what I mean about 'muddy fun'! Notice how the bikes have been developed for the sport and that the stages have been made harder to suit.
Again there were some small bikes taking part, including this 50cc Hercules.
There's a very good website about the ISDT which includes loads of photos (including the ones here), going back to the first event in 1913.
In 1964, the ISDT was held in East Germany and the USA team included actor Steve McQueen.
website of members, and brothers, Bud and Dave Ekins.