Hi all, I'm planning to "resto-mod" an old 70's frame with, most likely, a new 10-speed group. I'm probably just going to get a matching crankset for whatever groupset I go with, but I do quite like the appearance of some of the old fluted cranks that were common in the 70's or early 80's.
I was looking at some, and in many cases it appears the cranks have a BCD that isn't really compatible with wider-range gearing; many can't fit a smaller chainring than like a 40t. They're a bit uncommon but occasionally you can find a crank with a smaller BCD that theoretically could run a small chainring, such as the SR Apex in the first two photos I'll attach. However, it seems that you'd have issues getting the chainrings close enough that the chain might not get stuck between them. Are there any solutions that are feasible? Attached are photos of similar style cranks.
by gregn8r1
6 Comments
I think this is what you are looking for: https://velo-orange.com/collections/cranks/products/drillium-fluted-110-double-crankset-34x48t?variant=50648797127
There are surely five-arm cranks in that style with 110 BCD, which will allow you to run a relatively small rings (50/34, is the norm). In addition to that, there exist [these rings](https://www.ebay.com/itm/153939988775) which I have on my own bike, and let me use a 110 BCD square taper crank with my favorite chainring combination – 46/30.
You’d probably have to have shims of some sort between the crank spider and the big chainring, assuming the BCD even allowed for newer chainrings
Keep in mind that cranks of this era had little or no offset, so they are more likely to rub your ankle and are also likely to require a longer spindle.
Out of curiosity I went and measured the thickness of the chainring bolt tabs on the spider of my 10-speed 5-bolt 110BCD SRAM GXP crankset using a boley gauge/caliper, and the tabs are 3.5mm thick. That’s what I’m running on my 2×10-speed road bike with Tiagra 4700 shifters paired with Ultegra R8000 derailleurs using a standard 10-speed chain (SRAM PC-1051) and it works very nicely.
If the chainring bolt tabs on the cranks with 5-bolt spiders in your photos are 3.5mm thick or close to it (I’d say less than a quarter of a mm), they should work just fine with 10-speed 5-bolt chainrings if you can find the chainrings with the BCDs to fit the cranks.
It’s a shame new or new-old-stock Shimano-branded 10-speed 5-bolt 110BCD chainrings are getting harder and harder to find these days. Those shift nice and that’s what I’m using on my SRAM GXP crankset. https://matrix.redditspace.com/_matrix/media/v3/download/reddit.com/aizufgk35q5b1
Out of the pictures of cranks you posted, only the last one is something I’d consider for use with more modern derailleurs and chains. That one has a 110mm BCD, so the minimum chainring size for the inner ring is 34 teeth. That combines with a 50 or 48 big ring to give a range suitable for cassettes starting with an 11 tooth small cog, and a 1 to 1 ratio with a 34 tooth large cog.