38x16 without a motor.
38x16 with a slightly underpowered motor.
44x16 with a motor putting out enough torque.
For anyone interested in the decision process:
The cog on my Rohloff bike was 16T throughout; it has been such a success that the spare I laid in is also 16T. Sixteen teeth is Rohloff's default supply unless some other tooth count is specified by the buyer. The 17T cog SJS offered as a default must thus have been a special order.
The first crankset was an Indian Amar 38T steel job, popular as a budget set in Germany, which I ordered to replace the default Utopia Velo arms that I thought aesthetically sub-optimal, while I considered what would really go with my bike. The cheap Amar 38T crankset was in fact on the bike, inside a Utopia Velo Country fully enclosed chain case very much like the Chainglider but considerably more fussy in construction and rather fragile too, for some considerable time. (The Country is described in my tour through the varying chain cases on this forum.) The Amar was replaced when I spotted some rust spots on the back of the cranks at about the same time as I found acceptable cranks; the Amar chainring had hardly any paint worn off it in a couple of thousand miles, partly because of the spot-on chainline and high quality chain (KMC). Almost simultaneously the Country self-destroyed, and I decided to give the Chainglider a go.
The second chainring was the well-known Surly Stainless Steel, also 38T, chosen because it would fit inside the Chainglider and would presumably last forever, because I was already thinking about what was required on a zero or near-zero maintenance bike.
The Surly never got a fair trial. It was unmarked when it was replaced at 3600 or so kilometres because it couldn't be made to fit on my new mid motor when the front motor's electronics "asymptotically fishtailed towards their consummation in the final conflagration" (a description of one of my novels by the late John Blackwell, editorial director at my then London literary publishers of record). I do believe though that the Surly stainless chainring will make tens of thousands of kilometres.
The choice of steel rings after the Surly was exactly one. First of all, the chainring had to fit over the axle in the integrated bottom bracket by which the Bafang BBxx midmotor mounts into the bottom bracket shell. And, of course, the chainring had to be thin enough to fit the Chainglider, which eliminated the only custom-made chainring available, a thick ali job; presumably there are now more custom options, perhaps even including stainless steel, but I have enough suitable chainrings to see me out and I'm not embarrassed by a plain steel chainring, so I haven't been looking. After my good experience with the Amar plain steel, I had no hesitation in ordering all the Rohloff/Chainglider-capable and -approved tooth options for the Bafang motor with it. There wasn't a 38T option because it couldn't be made to fit the motor. On arrival and fitting and experimentation with the motor's torque curve in the software, after a while the 44T chainring stayed on the bike as the best match to the motor and to my requirements. It has given good service; even though I think expecting stainless steel-like longevity would be unreasonable, I am confident that these steel chainrings will prove to fit into my minimal service/maintenance concept, certainly far better than any aluminium chainring thin enough to fit into a Chainglider.
I keep a few tables of various transmission cog setups with a Rohloff at
http://coolmainpress.com/BICYCLINGHebieChainglider.html
