bottom bracket-mounted chain tenioner

[simonineaston]

Is anyone aware of a sprung / pivotting chain tensioner that is mounted at the other end of the chain run than is normal, i.e. up by the chain rings? Mostly, the job is done by the derailleur rear mech. cage, of course.

[jk49]

Black spire stinger?

[Brucey]

from the past; Osgear...?



cheers

[simonineaston]

Love it - whatever were they thinking?!

[jimlews]

New boy alert! My first post so please be gentle - I am not yet familiar with your protocols.

Fix-free drive made (perhaps still make) 'the incredible swing arm' that enabled the use of a double or triple chainset with hub gears. Comprised a steel clamp to attach to the chainstay, a slotted alloy tension arm for the two jockey wheels which were furnished with alloy chain guides and could be adjusted along the slots. There was some side float of the jockey wheels to allow the device to work for all three chainwheels and the thing worked very well. I rode from St Davids (Pembrokeshire) to Titchwell (Norfolk) and back using one in cahoots with a Sturmey 5. A nice system.

[BigG]

New boy alert! My first post so please be gentle - I am not yet familiar with your protocols.

Fix-free drive made (perhaps still make) 'the incredible swing arm' that enabled the use of a double or triple chainset with hub gears. Comprised a steel clamp to attach to the chainstay, a slotted alloy tension arm for the two jockey wheels which were furnished with alloy chain guides and could be adjusted along the slots. There was some side float of the jockey wheels to allow the device to work for all three chainwheels and the thing worked very well. I rode from St Davids (Pembrokeshire) to Titchwell (Norfolk) and back using one in cahoots with a Sturmey 5. A nice system.

Interesting. The combination with a Rohloff or similar wide ratio hub would be even more interesting.

[Brucey]

Love it - whatever were they thinking?!

yeah it looks weird doesn't it? But there is only one pulley to create parasitic drag, and some riders would fit a 'detensioner' control which took the spring tension off the pulley by a controlled amount (using a second lever), to reduce the drag still further. Apparently the capacity of the gear was limited by ground clearance...

cheers

[jimlews]

Thank you for your interest, Big G.

I am afraid that used with a Roholff the fix free swing arm would be entirely redundant, because they (Roholff) have already done all the work within the hub - a massive gear range (in comparison with a 1950s Sturmey Archer) and with equal percentage steps between the fourteen ratios.

For Interest, this is where I bought my 'Remarkable Swing Arm'.

Fix Free Drives
Brockhurst
Bagpath
Brimscombe
Stroud, Glos.
GL5 2SJ
Amberley (0453)873541

[beardy]

That must have been a long time ago with that phone number!

[Brucey]

New boy alert! My first post so please be gentle - I am not yet familiar with your protocols.

Fix-free drive made (perhaps still make) 'the incredible swing arm' that enabled the use of a double or triple chainset with hub gears. Comprised a steel clamp to attach to the chainstay, a slotted alloy tension arm for the two jockey wheels which were furnished with alloy chain guides and could be adjusted along the slots. There was some side float of the jockey wheels to allow the device to work for all three chainwheels and the thing worked very well. I rode from St Davids (Pembrokeshire) to Titchwell (Norfolk) and back using one in cahoots with a Sturmey 5. A nice system.

shimano make similar parts to use with their Alfine hubs, to further extend the gear range etc, but the tensioner is at the rear of the chain run not the front.

Big G is probably right for most solo use but there isn't a hub gear built that will (by itself) handle a gear range big enough for many pedal-drive applications.

cheers

[jimlews]

Love it - whatever were they thinking?!

In its day the Osgear was at the 'cutting edge' of bicycle technology. But even in its day it was a refinement of several pre war forerunners. It must be extremely difficult to come up with anything new AND effective.

In case I am thought to be a 'know it all' I recommend Frank Berto's Book THE DANCING CHAIN history and development of the derailleur bicycle.

[scottg]

Osgear works pretty well, first with indexed shifting.
The problem these days is finding 3 speed freewheels.

It is much easier to shift then the later Campy Cambio-Corsa or Paris-Roubaix mechs.