Thanks to Geoff Ingram for correcting some woolly thinking on my part! On reflection, I agree with his statement that the Scott compensator does not need to be mounted on the mudguard to function – the compressive forces in the upper and lower cable outers balance each other out so there is no net vertical component. There will be a small horizontal force due to the compensator being fixed to the mudguard, causing only a slight deflection. Mea culpa!
The same does not apply to the Vincent-style balance arm conversion which needs a mudguard mounted pivot, and very definitely does exert a large downward deflecting force. Hence the need to beef up the mudguard and its stays. This adds complication and weight but it does double the leverage making the brake twice as powerful. Of course the movement of the handlebar lever is also doubled – you don’t get anything for nothing.
I confess to being very surprised by Geoff’s assertion about “the best drum brake I have ever used” and apparently just needing a good clean and greasing. The comments received and read about over the years, and my own experience, all point in the opposite direction. Possibly he has a vice-like grip in his right hand – the legendary “six inch steel fingers” that Vincent owners used to say were necessary to stop their beasts. The Scott cast iron brake drums are very well supported by the hub and stiff enough to respond to heavy input loads without serious distortion, which may help to explain the success of the Vincent-style conversion. There is no escaping the very small drum diameter. Six inches is just not enough.
There is no escaping the fact either that sharing the input force between twin drums halves the force, also true of twin cables up to the handlebar. Actually, the compensator could have a slight edge here as the lower cables do not emerge vertically but a bit splayed, caused by the geometry of the internal balancing pulley. This effect increases the power by perhaps 10% ? Making sure that adjustments concentrate on the backplate levers will keep the pulley as low as possible. I have speculated about a modified compensator mechanism to multiply the force but it’s a difficult design exercise and none of my ideas look workable.