Agreed. A splined freehub that takes even 11T sprockets and is less than 10mm in width would be awesome
Lets see if we can find such a thing. It should be possible, since the downhill people who even use 15mm half axles can use 11T cogs.
Still I see now reason for using freewheels smaller than 13T: They fail too often, chain is waste very fast.
Or bigger than 15T: Uses too much space. To gain a 3:1 pedal to Jackshaft overdrive even with a 16T BSA FW you need a 48T chain wheel. Imagine how that looks If you want a 4:1 overdrive which isn't that absurd.
Got no answer form the factory this morning :? I'll post as soon as I now the new prices and the shipping date
With the chosen design we can have the following gearing range, without using the 4-arm 64mm interface adapter and using only MTB standard chainwheels:
Smallest: 32T Chainwheel, 15T FW, 16T ouput sprocket,
2.13 pedals->jackshaft overdrive, virtual chainwheel size:
34.1T
Largest: 48T Chainwheel, 13T FW, 23T output sprocket,
3.69 pedals->jackshaft overdrive, virtual chainwheel size:
84.9T
when using the 4-arm 64mm interface adapter:
Largest 48T Chainwheel, 13T FW, 28T output sprocket, virtual chainwheel size:
103.4T
What I aim for my QBPM setup: 42T chainwheel, 13T ACS 3/32" freewheel. So we will see with the 6:1 plenatery gear: 42/13x6= 19.38 motor to cranks reduction. At 85rpm crank speed we will see
1650rpm motor speed which is still fine for the Bafang QBPM. I'd like to have a cranks->wheel overdrive ratio of 5 (4 is MTB standard) in highest gear and I want to use a 15T-34T cassette, so I'll use 23T IGH output sprocket. The virtual chain ring size is
74.3T. This unique setup would just not be possible using the common freewheel crank setup.
When using the slowest 34T gear we still see the additional 6/5 increase in gear ratio due the planetary hub gear-> middrive conversion, so we gain a 34T/23Tx6/5=
1.77 increase in torque. The QBPM feels like spoked in a 14.65" rim instead of the rear 26" rim. In highest gear, it feels like a 33.22" rim. If we now enter this into the ebikes.ca we can see how it will perform both in highest and lowest gear.
on the flat
and on a 20% hill
The highest gear has 47.8% efficiency at 16.4kph max on that hill, the slowest has 79.4% at 22kph. What a huge difference!
BTW, I chose a battery voltage and wind that has 2200rpm no load motor speed, so 2200/5= 440rpm rim-no-load-speed, so the motor runs efficiently at the 1650rpm loaded (thats 75% of 2200rpm). As we can see this still is geared a bit too fast at 80.4% max efficiency on the flat road. With a gearing that has 29" wheel size I gain best efficiency of 82% for this battery-and-motor-wind setup.
So I should maybe use 20T output sprocket instead of a 23T and a 48T instead of the 42T chain ring to gain the same overdrive ratio.
That may be pushing it a bit, but will keep a eye out.
