SRAM AK2 freewheel

[cycle tramp]

Fair enough...

... perhaps the biggest benefit is that this two of everything transmission can be fitted into a frame design which uses a stub axle and only has a mono rear stay... and you could wrap both chains in an chain case/ oil bath for maximum chain life.

[Steve O'C]

Reminds me of the Hirondelle Retro-Direct. Not that I have ever seen one in the flesh.

https://onlinebicyclemuseum.co.uk/1935- ... -directes/

Steve

[rareposter]

Fair enough...

... perhaps the biggest benefit is that this two of everything transmission can be fitted into a frame design which uses a stub axle and only has a mono rear stay... and you could wrap both chains in an chain case/ oil bath for maximum chain life.

Yep - benefits are that it doesn't need a specific or specialist hub, just one that can take a freewheel. No shifter or cable (I appreciate that for normal "around town" use, that's rarely an issue but it's a definite extra source of problems on a bike of this nature being used in rural Africa!). Plus it's super cheap - the article linked to said the bikes were being sold at $180 which is about the price of a new SA hub on its own.

I'd suggest that adding an oil bath is unnecessary and simply extra weight and complexity - it's basically just 2 SS chains, there's no shifting, they're running in line so there's not a lot to need dousing in oil.

Clever bit of kit!

[Brucey]

except in special cases, I'd expect at least one of the chains to benefit from a tensioner

[rareposter]

Thread bump:

https://youtu.be/NnSWDKfT7FQ?si=Fl3sBFn47jQnDEOx

15-minute video going through the details of the new bike, the 2sp freewheel and some of the community stuff it does in Africa. It's both fascinating and inspiring!

except in special cases, I'd expect at least one of the chains to benefit from a tensioner

That gets addressed in the video, about 6'50" in.

[CJR18]

A couple of articles on World Bicycle Relief / Buffalo bike over on bikepacking.com :

WBR Kenya:
https://bikepacking.com/plog/inside-wor ... ief-kenya/

Touring on the S2
https://bikepacking.com/plog/bikepackin ... o-bicycle/

[rjb]

We need to see the freewheel dismantled so we can see how it works.

[CJR18]

https://patents.google.com/patent/US116 ... q=11655004

[st599_uk]

Or why not get 2 separate lightweight single speed bikes, say 9 kg apiece, one with a high gear and one with a low gear. Lash them together with a couple of cross members and struts and jump on whichever one suits for the terrain. This to me is similar engineering.

Presumably because a lightweight single speed bike can't carry 100kg on the pannier rack.

Buffalo bikes (for which this drivetrain was designed) are designed to be used in rural Africa, carrying goods to market, allowing girls to carry a days water supply quickly so they can carry on with their education etc. whilst being maintained with primitive tools.

[rogerzilla]

So.a proprietary component with no track record, and unnecessary weight and dirt-attracting chain. I thought AW hubs were pretty well understood in Africa, and they rarely go wrong?

[st599_uk]

So.a proprietary component with no track record, and unnecessary weight and dirt-attracting chain. I thought AW hubs were pretty well understood in Africa, and they rarely go wrong?

Is it proprietary? From what I read SRAM designed it but gave the design away to World Bicycle Relief.

[st599_uk]

...fair enough... I hope they supply the UK with their product as well... i might buy one

I think they were talking about making them available, but you may have to buy 2, one of which is given to a teenager in Africa

[rareposter]

So.a proprietary component with no track record, and unnecessary weight and dirt-attracting chain. I thought AW hubs were pretty well understood in Africa, and they rarely go wrong?

Watch the video I linked to a few posts up, it explains it all in detail.

These bikes have been in use for over a year now, they're at least as reliable as the previous generation Buffalo, if not more so.

And it got mentioned somewhere else on this thread - the price of an IGH, even a basic one, is more than the cost of this entire bike! ($180).

[Brucey]

except in special cases, I'd expect at least one of the chains to benefit from a tensioner

That gets addressed in the video, about 6'50" in.

not really. The chains being equally slack when new is one problem; that they stay that way as they wear is quite another. The chains are extremely unlikely to wear evenly. It probably makes most sense to tension whichever is the slower-wearing chain (probably the low gear one) normally, then to use a spring-loaded tensioner on the other one. The tensioner need only have one pulley if it is implemented in the right way.
BTW the cost to bike manufacturers who use a 3s hub in place of a singlespeed hub is about ten quid.