"One valid test is worth a thousand expert opinions." - engineering proverb

One issue that VegasJen has not yet considered is how would a new contemporary crank (either the inexpensive 12-speed one I linked above or an 11-speed model) work with her existing 9 or 10-speed drivetrains. Lots of variables there.

For example, I use 10-speed Shimano chain rings with an otherwise 11-speed Shimano drive train without issues, but she needs something else.

nonissue imo. Nothing sticks out as a real concern. LBS would unlikely support such setup.. it's not cookie cutter nor would all the part numbers be associated. Pretty much anything that the bicycle was never OEM fitted with would be backed by a retailer.

Nope-
Rear Admiral Grace M. Hopper
https://www.linkedin.com/pulse/one-a...pinions-hansen

So, you think, for example, that a 9-speed chain would work with a 12-speed crankset? I am not disagreeing, I just don't know; I had thought that the gap between chain rings in a 2x crankset is somewhat dependent on the chain.

I also don't know. But higher speed systems have everything thinner (and thus less durable, given the same material quality). So an older system like a 9 chain on 12 cogs and chainrings, I think the wider outside width of the 9 chain may be a problem on a 12 cassette with noise and possible unintended upshifts, and the wider inside diameter may be a problem on a 12 chainring as it may be less stable, may want to twist slightly.

No way is a 9speed chain fitting a 12speed cassette. There's a >1mm difference in chain width.

edit: I need to read more carefully.

if it were an eight speed cassette, I'd paint a different picture with my thoughts.
9+ cassette with 11 speed crank, i expect that it'll be ok. I haven't put raw numbers together to establish a professional data sheet, but even then a real world test can reveal different outcomes that calculated data might not factor.

I'd look on sheldon brown. The site has all the "official" data, but also tons of macgyver options, such as how to put 8 on a 7 speed freehub by using thinner 9 speed cogs, spacers and chain (IIRC), etc, and many more scenarios; I think if it can be done, they have details if it works and how to do it.

https://cimg9.ibsrv.net/gimg/bikefor...b9189cca0.jpeg
https://cimg0.ibsrv.net/gimg/bikefor...eb78c15f5.jpeg

on the subject of the Shimano bonded cranks - comparison of the bonded vs bonded / machined etc - great article on 6800 vs 5800 cranks - includes pictures and weights :

https://handsonbike.blogspot.com/201...o-105.html?m=1

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Yes, a 9 speed chain will work on a 12 speed crankset. The distance between rings on a crankset aren’t narrower, although the ring itself is narrower. The width of a chain is dependent on the cassette spacing, not on the crank.

I was only asking about using a 9 or 10-speed chain with an 11-speed or 12-speed crank (and chain rings), not the other way. I assume that VegasJen would keep her existing chain to maintain compatibility with the rest of the drive train. I understand from using 10-speed chain rings with an otherwise 11-speed drivetrain that cassette and chain must match.

​​​​​​​Even so, would the greater inner width of a lower speed chain allow the chain to slide laterally across the thinner teeth of the high speed chain rings, thus leading to faster wear?

You do look slightly over-extended in that shot, but I know triathletes do things differently to help the transition to running. 150 mm isn't crazy short, it's only 3/4 of an inch shorter than you're riding now. I expect many of us are thinking "I could sort this out for one of my clients", like I could slap on a used crank just to try, that might not work brilliantly (poor front shifting, noisy chain) but would give you a feel for the difference in pedal action, so you were confident in choosing a good solution.

I don't know anything about tandems, but if they follow bike fitting theories for road bikes, it would appear that the frame is too small for your wife. Is a longer seat post not possible?

Weren't 6 inch cottered cranks pretty standard issue on ladies' bikes up to the 1960s, along with 590 mm rims?

Her left leg appears to have reasonable extension in the 6 o'clock position.

If there was a lack of provision for female cyclists, it was all for their own protection from bicycle face

Nope. The tandem is the proper size for her. In fact, I was rather surprised that tandems came in a stoker size that was actually her size. She rides a 43cm road bike with 700C or 26” wheels. This frame is the same size. She has about as much seatpost showing as I do and the captain frame is exactly my size.

Don’t know. I haven’t run across any if they were. There’s lots of short Ashtabula cranks but it’s not like those can be used on that many bikes.

Superb article, thanks. My only questions are:
- For the ultegra spider, outer shell bonded to inner part, are they both aluminum parts or is one steel? If both aluminum, I can't see the advantage of bonding two parts together, versus the one-piece 105 spider, with both appearing to be same finished shape, especially at such small mass difference.
- Both ultegra and 105 outer rings show significant "depth of section", thicker, versus traditional rings. I wonder if it's to allow them to be lighter (ultegra is hollow, 105 uses a composite ribbed construction), or they did it to make the rings laterally stiffer (versus traditional rings), for greater shift precision?

The spider is steel iirc. Spindle is aluminium to save weight.

edit: nope, the other way round.

Good edit. :) That's typical. I just can't figure out why they would bond two pieces of aluminum together, to get the same net shape and near identical mass as the 1-piece cast aluminum 105 spider and crankarm. UNLESS... it's 2-piece to make the arm hollow? But it's only 9 grams lighter. Maybe the ultegra came first to market with that style, then later with the 105, they decided to be a bit less clever, make it 1-piece?

somewhere along the life cycle way, someone determined a penny could be pinched.
would like to see a CNC/waterjet cut aluminum assembly made using a thicker spindle shaft [ I.D. increase] that allows for two crank gears to be affixed to it using titanium hardware. would not want to see that price tag though!

For the crank length:
The amount you shorten the crankarms, you will need to raise your saddle a similar distance. This will also change the rest of your fit.
at 5'4" 150-160mm should work for you. It's all about the inseam.
Closer to 150mm for road and closer to 160 for MTB
You'll likely notice a higher cadence and less hip sway and maybe less saddle sores
Gearing might have to be adjusted depending how picky you are.

I'm only slightly taller than you and went from 170 and 175 and shortened them to 150 and 155. Later adjusted to 160-165 when I upgraded

I was going to go on a rant about crankarm shortening but the engineering nerds covered most of it, and it looks like you don't need it.

Final note:
If anyone uses BMX cranksets use caution
The chainline is usually around 43-45mm and not really suitable with most ROAD and MTB frames.

I did not know that! (thanks!)

Thanks for the info. I like that direction; For a press-fit into an aluminum bottom bracket, what happens if the press loosens over time, or is damaged somehow? Pressing into steel cups which are threaded, to me, makes a whole lot more sense, is more robust and serviceable, and if for some wild reason the press diameter becomes loose, you just replace the cups.