Chalo said:
DNP freewheels are pretty junky and failure prone.
Tell me about it. I've destroyed two of them! The big gear in each of them bent over like a toothless Texas truck stop lot lizard who just got into the passenger seat of a V12 Peterbilt with the methed-out operator in the driver seat, happy as can be.
That said, it was two of them in about 35,000 miles of use between them plus a free used Shimano 32-14T freewheel given to me from a local bike shop(still usable, unlike the DNPs), but still... one of the DNPs went out within the first 4,000 miles of use while I was spinning up a 20% grade at 8 mph in a 22T front chainring, before ever installing a motor.
There's another concern when setting up gearing on a rear hub motor, which is the tendency of the freewheel thread to break out of the sidecover when pedaled too exuberantly. There best way to mitigate this problem is to use the largest sprockets that will give you the ratios you want, thereby lowering the chain's operating tension. So rather than using an 11 rear sprocket to get a tall gear, you'd bump up the chainring size. 66/14 is the same ratio as 52/11, but 79% as much chain tension for the same power.
Duly noted. I like the 11T in the rear because I need the widest possible gearing range I can get, and currently don't have the funds to justify a Schlumpf drive up front yet. There's also the issue of the KMX frame not being compatible with a small rear gear larger than 11T, forcing me to lock out last gear if it is larger than 11T due to chain clearance issues. I don't find myself using the 11T gear more than about 5% of the time since I cruise around 30-35 mph, but sometimes when I want to go downhill at 45+ mph, the 11T comes in very handy. I can do 46 mph on flat ground, also in the 11T, using my current 46.8V 10.5AH 1500W pack. Once I upgrade to a 72V 21AH 5 kW pack, that top speed could improve to 60+ mph even though I'd be pedaling like a madman to do it as a 52/11T combo is at my sustainable-for-more-than-a-few-seconds cadence limit around 55 mph with a 26x1.5" rear tire.
I tried a countersunk bolt for the seat stay mounting post with a freewheel that had a 14T small gear and it did not solve the issue, as I needed an extra 0.2-0.3mm or so of side clearance still when using a freewheel with a 14T rear gear. Going to an 9-speed chain may be just enough to clear it, but that is an expense I am not currently prepared or willing to make when I have a perfectly fine 7-speed chain with no indication of stretch yet at about 4,500 miles, cheap as a 9-speed chain may still be(I've been living on the financial margin as it is, and have been keeping this thing running for dirt cheap doing 30-40 miles a day, although if I get this new engineering job, my mom won't lose her house and I won't be looking at the possibility of having to live out of this thing in the near future either).
I might go to a 6-speed freewheel setup in the future to free up some axle space on the next motor I order, as there are 6-speed grip shifters available, and I can find high-quality 6-speed freewheels that are 34-14T and 30-13T. With a Schlumpf drive, I could have a more than adequate gearing range for my needs, while deleting the 7th gear should free up enough space for the chain not to get snagged on the seat stay mounting bolt.
I could see the cycles of impulse causing metal fatigue. So you're saying each tooth on the sprocket engaging and disengaging with the chain causes pulses in the amount of torque transmitted to the wheel?
