It’s strange to think it, but today the disc brake is often thought of as a relatively modern invention and the drum brake as yesterday’s method of retardation, but when you do some digging, you see both arrived at roughly the same time.
Opinions differ as to who was exactly ‘first’ with the drum brake, but in 1902 it was either Ransome E. Olds of Oldsmobile (and later the creator of the REO Speedwagon which later became the name of a band) or Louis Renault who invented the drum brake. So, take your pick….
First designs were of an ‘external’ drum brake, but soon the more elegant ‘internal’ drum brake was designed. Why? Well, the external drum would get clogged and fouled with all sorts of mud, dirt and detritus. The internal drum brake is pretty much what we have in use on our classic machines today. It’s just two opposed brake shoes being hydraulically (or otherwise) forced or pulled against the inside of the drum to create friction which therefore slows you down.
While the simple principles behind the internal drum brake have largely stayed the same, changes in design and materials used have meant big advances in performance – so much so, that early discs on motorcycles (think CB750 et al) weren’t necessarily better than the refined drums seen on bikes of the time… Also, for a while at least, the humble drum brake set up proved to be cheaper to manufacture for some years, hence it was seen on the cheaper motorcycle for many years after it had fallen out of favour on bigger, more ‘performance’ oriented motorcycles.
But, as good as they are/were there are a number of big disadvantages to the drum brake. Firstly – and most important on motorcycles – they had to be pretty large to cope with the stresses and strains involved in slowing down around 300 kilos of bike and rider… Racing of course rang in the changes and – as more powerful/smaller braking systems were needed – the move to discs soon came about.
The other issue with drums was consistency. Heat generated by the friction often led to degradation in performance, so some drum brake systems would incorporate ducting/vents to aid cooling. And, with the drum itself expanding as it got hotter, the shoes themselves had to move further to make contact with the inside of the drum. Drums were also more in need of regular tweaking and adjustment than a modern brake disc set-up.
Of course a good twin-leading shoe drum can work brilliantly well and – if the drum diameter is spot on, the issues are not so apparent. Doubtless drum brakes will be with us for years to come…