One thing that doesn't seem to be have discussed :

- What effect does using a worn chain sprocket, chainring have on the transmission efficiency ? To me, a new chain and sprocket "feels" more efficient than a worn transmission, but some of that is probably psychological.

👍

But better if I could have added it to Dan’s post!

What I meant, George, was that after seeing how badly worn the sprocket was that PH posted (which was obviously in use) that perhaps we all change them too soon.
A 1:1 final drive is much more tolerant of wear than a derailleur system……where almost invisible sprocket wear can give problems as different sprockets will have different amounts of wear so some will not mesh with the chain.

Agree.  As noted above, I have started to put worn out chains from my derailleur bikes onto my Rohloff bike, depriving my Rohloff bike of having newer chains.

That exceptionally worn out sprocket that PH showed the photo of had 16 teeth, an even number of teeth, you can see that several teeth were broken off but in that case those broken teeth were every other tooth.  I mentioned above that Rohloff hubs are usually fitted with a 16 tooth sprocket when new if you did not buy it on a bike from Thorn.

I also think that Thorn bikes that use a eccentric bottom bracket may be more tolerant of wear than ones that use a spring loaded chain tensioner.  With a very worn chain on a very worn sprocket, as you pedal, each chain link will climb up each tooth as the wheel rotates, causing more tooth wear.  The limiting factor on how high a chain can climb up a tooth with a spring loaded chain tensioner is the spring, thus if you pedal harder the chain could skip over the teeth.  (Like happened last summer on one of my derailleur bikes, the chain was not yet at 0.75 percent elongation but some sprockets on the cassette were sufficiently worn that the chain skipped when pedaling hard.)  But with the Thorn eccentric, as long as your chain is not too loose, it won't skip because there is only a limited amount of extra slack in the part of the chain that is normally loose as you pedal.

I might have mentioned above that I am going on a tour in the near future, not sure which chain to put on my Nomad Mk II for that trip.  I anticipate a bit over a thousand miles on that trip.  And I expect it to have more wear than normal as the bike will be carrying a heavier load, expect it to be exposed to wet weather more often, and probably will get less lube than typical.  But I do not want to put a chain on that has so much wear that I could be asking for trouble.  The chain currently on the bike has the eccentric near the maximum for amount of chain tightening that can be applied.

I found one chain in my collection of used chains that has a bit over 0.5 percent wear from a derailleur bike, I think that is the one that I will put on for my trip.  It should still have plenty of life left on it, so it should not be troublesome on my trip.  Maybe I should swap chains today, and measure my old one for percent elongation before I discard it?

The 👍 also helps reduce posts basically being duplicated by others.

Due to poor health, I am reluctantly offering this exceptional tandem for sale. It has been a much-loved vehicle for our family, and I hope it brings its next owner as much joy as it gave us. Personally ordered from and built by Robin Thorn (Serial No: 200312006), this "Long/Short" aluminium frame is the ultimate setup for a tall captain and a child or petite adult stoker.
Key Features:
•   Child-Back Style: 16.5" rear seat tube, adjustable stoker stem, and specialized 150mm short-reach rear cranks for a perfect, safe fit for smaller riders.
•   Maximum Gearing: A "wide as possible" 3x8 (24-gear) range controlled by intuitive GripShift on flat bars—conquers any hill.
•   Premium Comfort: Upgraded with genuine Brooks Sprung Leather saddles (small profile on rear) and high-volume Schwalbe Hurricane 2.1" tyres for a beautifully cushioned ride. Brooks Flyer saddles front and (Short) rear tensioning tool included.
•   Heavy Duty: 36-spoke wheels for maximum strength and reliability.
•   Touring Ready: Includes high-capacity Thorn front and rear pannier racks.
Condition:
Very Good condition throughout. Professionally serviced with brand new chains and a new rear derailleur; it has been ridden only once since.
Sizing:
Front Seat Tube: 21" (32" Standover) | Rear Seat Tube: 16.5" (27" Standover).

•   Extras: Thorn high-capacity racks (F+R), adjustable stoker stem.
Service History:
Major service 2 years ago including new chains, brakes and rear derailleur. Only one ride since. Very Good condition.

Offers over £600.

I can supply photos, just tech glitch won't allow it on here today!!!!

Location: West Sussex (Local collection)
Contact: Richard Broadhurst (muddypair@icloud.com / 07724807380)