The first disc brake?
When was the first disc brake fitted to a cycle? All the new motorbikes and even expensive bicycles have them of course, but it wasn’t always so. Just like so many other items, they were around 100 years ago. (Just for fun, here is a partial list of that 100+ year old tech: Transverse 4 cylinder motors, Water cooling, Telescoping forks, Monoshock rear suspensions, etc.)
Quickly defined, a disc brake has just two things: a disc and a caliper. The caliper has TWO or more pads that are actuated in the axial direction (along the axle direction). Drums have one or more pads or shoes that move radially away from the axle centerline. Exceptions occur of course.
The common answer the question is the Honda 750 or the Lambretta scooter. Those were relatively early examples of motorbikes with factory installed disc brakes. Going earlier, some folks claim the Douglas Reseach Association (RA) of circa 1922 as a disc brake.
But the Duggie was really just a dummy rim brake as was common in the 19teens. The dummy rim is spoked to the hub, with a shoe rubbing against it to decelerate the bike. Douglas’s invention was to cover the steel rotating rim with braking material instead of making the brake shoe from braking material. But otherwise, it looks very much like the rest of the brakes of the era. Dummy rim brakes had a V groove like the RA, sometimes the V was facing inward, sometimes outward. But the braking action was always from a shoe moving in, towards the axle. Just like the RA does. A good description is here, which is also were I found that photo. Click the link to read more about why it isn’t a disc brake. 
FYI, here is a BSA with a similar front brake, but the V is inverted compared to the RA. Sunbeam had one too, as did many of the makers of the era.
For more pics of a typical V acting brake from 1913, with a V groove just like the RA, acting radially (this one acts outwards instead of inwards) onto a V rim that is spoked to the hub, click here to see how to make brake parts: https://occhiolungo.wordpress.com/2010/10/18/how-to-veteran-motorcycle-brake-blocks/
But if we go back further to the turn of the century, we see this Abingdon Axle. It has a caliper acting on a disc, although it uses cable operation not hydraulic fluid. Note that the caliper has two brake pads that moved axially towards each other. The V that is visible is the belt pulley, and is not part of the brake action. This terribly fuzzy image is from James Sheldon’s book, and I wish that I had more info than that. Has anybody ever seen a c1898-1905 De Dion fitted with a rear disc brake? Send your comments via the link.
This topic continues here: https://occhiolungo.wordpress.com/2013/11/10/first-disc-brake-continued-national-motorcycle-museum/
and continues further here: https://occhiolungo.wordpress.com/2013/11/18/the-first-disc-brake-part-3/
PS, Blaise D. sent in this from wikipedia for early autos:
History
Disc-style brakes development and use began in England in the 1890s. The first caliper-type automobile disc brake was patented by Frederick William Lanchester in his Birmingham factory in 1902 and used successfully on Lanchester cars. However, the limited choice of metals in this period meant that he had to use copper as the braking medium acting on the disc. The poor state of the roads at this time, no more than dusty, rough tracks, meant that the copper wore quickly, making the disc brake system non-viable (as recorded in The Lanchester Legacy). It took another half century for his innovation to be widely adopted.
Added Jan 17, 2014: This view from the VMCC brake supplies shows essentially the same brake as the Douglas, as fitted to many bikes in the 19teens. Note the inverted V cross section shape that was previously dictated by the V belt, and that the brake shoe has that negative V shape just like the duggie. And the trailing shoe action like the duggie. But the brake material is on the shoe, not on the rim. Moving the brake material to the wheel’s dummy rim was the novelty of the Douglas, but the braking action works the same as all the others. 😉
Occhio Lungo 
Ah, it begs the question; is a DeDion tricycle a motorcycle? No comment on that, but I do credit Douglas a ‘first’ for using the Research Association disc brake, for it is clearly a disc, even though it doesn’t use a caliper clamping on the disk for braking power. The RA disc isn’t a dummy rim, but clearly a different animal, far more recognizable as a modern brake, even if the method for applying pressure is the same. A step in the right direction, at least…
We’ll have to disagree on the RA Paul. It is a dummy rim, spoked to the hub just like so many others of the 19teens and 1920’s. The even the V angle is likely the same (some brakes had the v facing inwards, some faced outwards). The RA steel rim has brake material applied to it, but that’s a very small difference from having a steel V rim and putting the friction material on the moving shoe. 🙂
Fine line there Pete. I’d consider the Douglas design a disc as well. It fits by your own definition of a rotor and caliper. Whether the faces of the rotor are parallel and regardless of the fixing method of the rotor the principles are the same.
Sorry Rick, I consider a caliper to have two moving pads that move axially. The RA just has one shoe that moves radially. It doesn’t squeeze the ‘disc’ any more than all the other V shaped dummy rims that existed in the decades before Douglas did the RA brake. But I’m open to discussion. 🙂
Boy, if I only had a time machine I could go back in time and really impress the motoring public with my six piston calipers on floating disks. Hopefully my time machine would have brakes capable to stop my passage back thru time before I enter the dinosaur period. I should probably bring some matches…
To add to the discussion here, the “first” of anything mechanical often looks quite unlike the modern result. Is a Stirrup brake a caliper brake when it uses radial force instead of lateral?
Many disc brakes on aircraft are a bit “inside out”. The caliper is in multiple segments, with the disc(s) keyed or bolted to the wheel rim, not the hub. Some of the caliper parts do not move. So . . . disc brake or rim brake?
Not to necessarily disagree with you guys, but sometimes you just have to agree that clear is clear, and fuzz is fuzz. I happen to agree with the Douglas because the disc is NOT useable or similar to a belt pulley (show me a belt that would have worked with it).
Interesting discussion.
Les Westlake
Good points Les. But that Douglas was just like so many other dummy rim brakes that were around on front wheels. No belts, just V shaped brakes. Some had the V point going inward like belt pulleys, some outward like the Douglas, but they all work the same as the Douglas. The Douglas didn’t do braking any differently than the other brakes, it just put the friction material on the wheel instead of on the moving lever. Triumph had the same shaped brake 10 years earlier fitted to a rear wheel.
If we define disc brakes as having a rotating disc and a caliper with two axial moving brake pads, then the Douglas just doesn’t fit at all. And there is no denying that the c1900 disc brake preceded it with a real caliper anyway.
But I love to hear more discussions on the early stuff. I’ve always wondered if some steamcar, shop lathe or horsebuggy or something had a caliper brake in the 19th century…