groberts wrote:I hope (?) they were badly set-up because otherwise, as previously said, I found them to be dangerous. After using a 'normal' freewheeling bike for years - like most people - it is, I would think, common practice sometimes just to adjust the crank position from time-to-time when not actually pedalling e.g. coasting. Furthermore, the said mechanism made hill starts almost impossible, as it was difficult to position the cranks in such a way to achieve downward pressure to move forwards on the first stroke, if you see what I mean?
Not really. Ideally, stop with the pedal up ready to set off again, but if not, scoot the bike forwards while turning the pedals into the correct position, or in the worst case, left the back wheel and turn the pedals forwards.
It sounds like the coaster brake was functioning normally: mine gave between an eighth and half turn backwards depending on gear before it started to engage, progressively. I think if the lubrication is imperfect (which Shimano's specification is, I think - ask Brucey!) then it can "grab" more aggressively than it should and it sounds like that's what you were suffering.
It's not really the coaster brake that's dangerous IMO. It's the bad habits of backpedalling to adjust crank position (pedal forwards! It's kinder to the chain) and of lifting pedals while stopped (taught by Bikeability IIRC) which are dangerous, especially when you ride many different styles of bike. OTTOMH, both the very common coaster brakes and the less common kickback gear shifts will surprise you often if you're in the habit of backpedalling.
I find it worrying / baffling that this mechanism is so widely used and bizarre that it might be a response to those (surely only a few) that might have problems with brake levers - using disc brakes and / or various ways of enhancing the pull with mechanical or pneumatically assisted brakes is surely a better option. As a matter of interest, I presume the brake effect is in the lower power mechanism and works by reversing the electric assistance?
I think it's widely used because it's so simple and means one less lever and cable run to maintain. It is also very cool to be able to brake with no hands.
The brake effect comes from the backpedalling pushing out brake shoes inside the hub so they press against part of the hub shell, so it's a type of drum brake, but it's stopping a lot less weight than a motor vehicle so it's pretty effective.
Just to make matters worse I found the Shimano Nexus 8-speed hub gears also worked poorly, [...]
I think I've read that the higher-numbered hub gears (8 and 11 speeds) are rather sensitive to cable adjustment, which is less than ideal for a hire bike where you don't know who's fiddled with what and the shop probably doesn't give it long enough test rides to spot problems developing, while the 7s and Rohloff's 14 are more robust.