motogrady wrote
Rimlocks over here.
If I might ask, what are the main differences between a featherbed and a featherbed slim?
The Manx "featherbed" was the first edition of the famous frame. It was made in very limited numbers specifically for racing and made of 16 gauge Renolds 531 manganese-molybdenum steel alloy.
It's simplistic double-sided, single-loop, head-stock to head-stock design made it easy to manufacture yet extremely strong, while also making gas-tank fitment really easy due to its "flat" top rails.
A road-going version was made, this time out of more economic thicker gauge, grade "A" mild steel, but almost identical in shape, which later became known as the "wideline". The main visual difference between the Manx and the road-going wideline (apart from the narrower gauge tubing) is the curve of the rear frame rails begin earlier on a Manx and therefore has a gentler radius than the road-going wideline. The difference is fairly minor and it can be difficult to determine a Manx from a wideline in photographs.
Some riders commented that the wideness of the frame rails at the point where the seat met the gas tank caused discomfort on the inner thighs on the wideline featherbed, and so in 1960 the Slimline featherbed version was introduced with the top frame rails "pinched" at the rider's thigh position to allow for greater comfort. The rear shock support arms were also changed from being a straight strut to being a curved support, and with larger upper shock brackets. These curved shock supports and larger upper brackets are the easy way to spot a slimline over a wideline.
As the slimline frame rails are narrower as they extend rearward, the gas tank fitted to the wideline no longer fit the slimline, so a new, taller gas tank (and seat) was designed. This makes it very easy to spot a slimline or wideline when in standard form (as in OldIron's original picture above).
.