9/10 speed chain with vintage 2x5 crankset

Question

I have an old crankset from an 80s 10-speed (2x5) bicycle with downtube friction shifters. The chain currently in use is marked as "6/7/8 speed," but works fine on the 5-speed freewheel. For a multitude of reasons, one being the need for more gears, I have decided to replace the rear wheel and 5-speed freewheel with a freehub system and cassette sometime in the near future.

I know from riding the bike that the current 8 speed chain presents no problem to the front chainrings, but I would like to fit a 9 or 10 speed cassette onto the rear hub, which will necessitate a narrower chain. I would like to avoid having to replace the front crankset.*

I've read safety warnings online of using many-speed chains with few-speed chainrings, but given that my crankset was designed with a 2x5 system in mind (not 2x9 or 2x10), I'm especially worried about using a narrower chain.

Would a vintage 2x5 crankset be okay with a narrower 9- or even 10-speed chain? Or should I keep the 8-speed chain and "only" upgrade to an 8-speed cassette?

*Tangentially relevant: 9- or 10-speed square taper double cranksets don't seem to exist at all! Replacing my current 52/42 setup with a more modern 10-speed Hollowtech, or converting to a 1x system isn't out of the question, but I'd like to save as many of the original parts as possible while still keeping the bike usable by modern standards -- which means binning the old 14-26 freewheel.

EDIT: I want to thank @MaplePanda for explicitly wording my biggest concern in a comment:

For learning purposes: I’ve heard you run the risk of the chain getting wedged between the chainrings if you run a high speed count chain on a low speed count crankset. Is that an actual possibility? – MaplePanda

To be clear, this is precisely the safety issue I was referring to in my question above. I am not aware of any other potential issues with crank and chain compatibility, though I am of course open to learn.

Answer 1

Usually doing this on random old road cranks works without issue. You may find it's necessary or helpful to go to a front derailleur that matches the chain width. The reason is that if you run an FD that has a cage inner gap width that's much wider than needed for the chain like you would if you're pairing a 5/6 era FD with a 10 speed chain, you can run into the issue where for example by the time you have the FD high limit out enough for it to shift smoothly onto the big ring, the gap on the other side is too great and the chain can drop. Personally I would skip right to doing a matching front derailleur.

The chainring spacing doesn't really matter in almost all cases when it's a friction shifter like this. It does mean it might not work if you went to STI etc, between the spacing being weird and also no shift aids on the rings.

If you want to do this and know you don't need to mess with anything on the crank/FD end, just do an 8-speed cassette since you're already happy with how the crank and FD are working with an 8-speed chain. The other thing to consider there is how happy you're going to be shifting friction on the various options. Friction 9 and 10 speed isn't necessarily a problem and it can work okay, but it's not to everyone's taste. It also depends on how easy it is to make small adjustments with your particular friction shifters. The best ones are good about that (Suntour Power Ratchet is the poster child) but many will have you moving it in bigger chunks to overcome the stiction than you want for that purpose.

Answer 2

I successfully use a triple crankset with chainrings from a 15 speed (3x5) with a 9 speed rear cassette and mech. The chain is a 9 speed, and it all works well enough as a 27 speed, (3x9)

Remember all bicycle chain you're likely to find is 1/2" pitch so 5 speed through 13 speed is all the same spacing between rollers. Where it varies is the width between the outer plates.

If your cassette and rear mech are 9 or 10 speed, you should run 9 or 10 speed chain because fatter 5 or 6/7/8 speed chain may not fit between the cogs properly.

At the front end, the Front Derailleur pushes the chain around from the outside so a thinner chain simply needs the cage to move a little further. This can mess up indexed left-hand shifters to the point they need overshifting to compensate, or you can compress the cage's spacing carefully. You can even use a 9 speed front derailleur if you have one, but I wouldn't buy a 9 speed FD unless the other solutions don't work.

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Your current use of nominally 6/7/8 speed chain is fine with your 5 speed parts - all three are very close in width to each other because 6/7/8 speed cassettes simply got wider, rather than cramming more cogs in the same space like 8~9~10 etc did.

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As for the freewheel, yes the design becomes poor at 7 speed and unworkable at anything higher. The drive-side bearings are in the hub, and the downward force is on the dropout. So there's a longer lever arm of unsupported axle which is prone to bending under load.

Cassettes eliminate this by having the drive-side bearing much further to the right, inside the cassette.

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For your bike, keep all the takeoff parts. Clean and lube them, and store them well-labelled and together. This lets you revert to "original" later on if you choose to.

Your minimum upgrade would be a cassette-based rear wheel, the new 10speed cassette, new 10speed chain, a suitable derailleur, and right-hand shifter.

I'd suggest using new gear cables too, and possibly redoing the outers. You might choose to replace the left-hand shifter to make them both look the same, but that's personal preference. I've got a working bike with indexed rear shifting and a completely friction front shifter.

Good luck!

Answer 3

Short answer: you can't combine your 80's 5-speed crank set with a modern 10-speed rear cassette. The chain you need for the one does not work on the other. When I needed a new rear wheel in my 70's bike 12 years ago, I decided to just buy a new bike. The old bike is now in a museum.

Answer 4

I have 50+ years of bicycle touring experience. I found that standard distance between crank sprockets worked fine regardless of how many freewheel cogs were used. I may add, however, that it's never wise to go from inner (smallest) crank sprocket to outer (smallest) freewheel cog. That combination will wear your chain and sprockets out pretty quickly. It causes the chain to wear out (i.e. stretch) the quickest. I used to ride my bicycles around ≈14-18,000 miles per year. I also rode my loaded touring tandem (≈500 lbs.) for ≥14,000 miles in 1981-1982. A heavily loaded touring tandem will wear chains and sprockets out very quickly.