John, great write up. Thanks very much. I've just posted this as a reply to your write up and will copy it here:
I've just bought a new one this week (August 2020). I've been riding/building/modifying tandems and folding bikes all my life and have 35 years tandeming under my belt. Here is my take on gears:
Yes the current models come with the 14-28 freewheel and now a 36T chainring. This is a drop down from the 42T chainring on John's older bike. I assume this was to generate a lower hill climbing gear because, as we know, tandems do not climb so well. Trouble is, this gives a gear range of 25.71" to 51.43". This is fine uphill but useless anywhere else. Basically at 51.43" top you are really spinning at 9mph and have to coast at 10mph until speed drops. No good on a tandem. This is not a criticism of the product which is built to a price remember. So, what to do? Well I've considered ALL possible options and have concluded there is only one perfect upgrade for the bike which retains the very low hill climbing gear a tandem needs alonsgside an acceptable top gear for decent cruising speed. I have ordered the parts and will update here when complete and tested. First up is to ditch the 36T drive chainring and go with a 46T instead (yes there is frame clearance, just). This is a simple £13.72 upgrade from
Ebay. Next is an 11-34 freewheel (Megarange) similar to John's cassette. If you can not go above 46T chainring (which you can't) on a 20" folder then you NEED an 11T sprocket, anything else is a pointless upgrade. Such freewheels are very rare and no longer made by Shimano because of the propensity to use a modern cassette. Of course, as John describes, a cassette needs a new hub and wheel re-build so a suitable freewheel is preferable if one wants a simpler solution. They can be found if you hunt around. Better still DNP make one especially for E-bikes with extra heavy duty freewheel components to handle the incredible torque generated by an electric motor. This is ideal for tandems that also generate double the torque of a normal bike. Said freewheel retails for £40 but is currently available on Amazon under DNP's new brand name of Drift Maniac for just £25.72 with free delivery. This is a bargain (e-bikes use standard freewheel hubs of course). Current link here:
Amazon product ASIN B07XZ64MJ8View: https://www.amazon.co.uk/gp/product/B07XZ64MJ8/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
This combination of 11-34 freewheel and 46T chain ring maintains the very low gear for steep hills of just 27.06" whilst giving a decent top end cruising gear of 83.64". This range is ample for a 20" wheeled bike that has to manage on what is effectively only 6 speeds with an extreme 'granny gear' for when needed.
As for chains you should change this too. If you increase anything you should increase the chain length to match. The existing chain may work but only by over tensioning the rear gear pullies which in turn causes the chain to jump when on the biggest sprockets. The existing chain is 107 links and seems correctly sized so my upgrade to 34 tooth freewheel and 46 tooth chainring requires a new chain length of 115 links so a standard 116 link chain is an ideal option.
Hope this is of use to other Ecosmo buyers. The result is a good all-round compromise at a bargain price that means I have a tandem that folds in seconds and fits, would you believe, into the boot of an Astra hatchback with all seats raised!
