Short crank arms for bbshd

[Recumbentrx]

After looking all over the net for 155 crank arms for my bbshd’s I finally decided to solve the problem myself. After my second knee surgery I tried to ride my recumbent trike, (Terratrike Gran Turismo), two wheeler, (RANS Stratus Xp) and my semi recumbent crank forward mountain bike (RANS Dynamick), all fitted with a bafang bbshd mid drive motor mated to a 26” rear wheel laced to a nuvinci N380 cvt internal hub and a Paul’s components chain tensioner. After lots of trial and error, I found this setup to be the perfect setup for a recumbent commuter and former recumbent shop mechanic. That’s a topic for another discussion but I can say with upmost confidence that this setup works flawlessly. So on to the main topic here- what to do about replacing the garbage flimsy crank arms that came with my motors. First off, 170 cranks are too long for most cyclists but again-a different topic. So because I needed shorter cranks here is what I did:
First, I took an old set of cranks that we’re good candidates to shorten. They had enough flat metal where I needed to drill and tap new holes. I picked up a park tools pedal tap kit, drilled 33/64 holes through them at 155 mm, tapped the threads in and first tried to mount them to my bafang. No luck. They interfered, especially on the drive side. So I went on eBay and bought a pair of Promax SQ-1 single speed cranks ($58 free shipping) to experiment with so I didn’t have to make another mess in my shop drilling and tapping! This time before anything else I bolted them on to make sure they would work and the did. They fit and cleared on both sides no problem. Of course being mechanical minded, I took them off, cut off the chainring spider on the right side and trimmed a little bit off the left side where the base of the cranks were a little close to the motor housing. After grinding the aluminum down, wet sanding it to 1200 grit and cleaning them with alcohol, I sprayed the cut areas with automotive primer, paint and clear coat before re-installing them. You can’t tell they were brutally assaulted with my gringing tools! They are now on my long wheelbase two wheel bent and it worked out so well, I bought two more pair, one for my trike and one for my crank forward! As soon as I figure out how to post pictures here I will (I can build a bike or a house from scratch but can’t figure out technology, I know!!)

 

[markz]

As soon as I figure out how to post pictures here I will (I can build a bike or a house from scratch but can’t figure out technology, I know!!)

Thats exactly what I was thinking

Pictures or it did not happen :wink:
Why that phrase, well its a fishing jab and well its fishing weather today :wink:

 

[amberwolf]

As soon as I figure out how to post pictures here I will

There is an Adding PIctures thread at the top of every forum thread list, which includes a number of ways.

 

[Balmorhea]

First off, 170 cranks are too long for most cyclists but again-a different topic.

That’s complete nonsense. That length was settled upon because it works best for cycle racers, who average significantly shorter than the population as a whole (if you’re not talking about a population of Filipinos). Most adult men would be better served by longer cranks, not shorter.

If full length cranks don’t work well for recumbents, that’s indicative of a problem with recumbents (one of many that make such bikes very unpopular), not with adult length cranks.

That said, 6” or 152mm unicycle cranks are a direct swap for BBSHD and BBS02 cranks, and are often very inexpensive. I have installed them in the past to help pedaling cadence keep pace with motor RPM.