Thanks for reminding me, Martin:
I should've mentioned that the constraint behind my choices of chainring tooth counts is those that take Chaingliders, which are simply too useful to give up for some notionally "perfect" gear ratio; there is always another way to skin a cat.
And equally, I aim at cruising at my comfortable cadence of 40rpm on the level in gear 11, which is a 1:1 ratio, saving overdrive gears 12, 13 and 14 for fast downhills. Not that I'm on the flat all that often, but if you set up a Rohloff so that 11 is your most used gear, a lot of other possibilities fall into place -- for instance, after I fitted an electric motor, I could avoid the Rohloff's lower 7 gears by using the motor's software "gears" if I wanted to, though I don't.
You may ask why I worked up a complicated table for myself with a cadence of 60rpm when I'm comfortable at 40rpm. The answer is that 60rpm multiplied by 60 minutes in an hour has a red notch on a pilot's slide rule, and I'm comfortable working mental arithmetic on a base of 3600. For instance, 40rpm is 2/3 of 60rpm, so I eyeball a number, say a speed, on a different table and can instantly see how realistic it is; or I could argue that 2/3 of 3600 is 2400, which is pretty close to a quarter of 10,000, actually 9600, close enough for a first approximation or a check that you're working in the right direction; you can see that it makes mentally shifting the decimal point a lot easier. Martin's cadence of 90rpm is one and a half times 60rpm, so the result should run in the other direction, an easy division by two and then adding the product back to the base, result same as multiplying by 1.5. To be clear, I don't have the eyes any more for the small print on slide rules or the rotating slide rule bezel around a few of my watches, but I don't really need to see them; from long use I effortlessly picture them in my mind's eye. I fondled my pocket Pickett a bit and then slid it back into its leather sheath.
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BTW, Martin, a central motor installation isn't all that much more expensive than a front motor. It's the bigger battery you need when you go from a lower power front motor to a beefier mid-motor that raises the comparable cost appreciably. Also, the front motor that I had, despite its reputation as the Little Hill Climber, seemed more lightweight than the central motor, in every aspect but especially the control electronics, which were clearly not an in-house production in the case of the front motor. It might be that the front motor was built light to earn its title on the hills. Don't get me wrong. The front Bafang motor lasted lonhrt than any of my Nexus boxes, and the central Bafang motor seems likely to see me out, so I don't have any complaint about value received; I'll buy Bafang again, if necessary. But, if you're planning to make a permanent installation in the first instance, I suggest the central motor would be more satisfactory in the long term. The reason I made a sacrificial front installation was because there was very little known about these motors at the time (except for power-crazy Americans building electric motorbikes), so I was educating myself, but that no longer applies. There's a lot of experience of electrical motors on bicycles on this forum and elsewhere.
