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why aren't there any 2x5 groupsets? (slrpnk.net)

submitted 3 months ago by vomitaur@slrpnk.net to c/bikewrench@lemmy.world

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As a novice, I come seeking wisdom.

I have an old Rockhopper that I'm looking to strip down to the frame and rebuild into a commuter. I've been learning a lot about gearing and all that, and have been researching parts. I see that there are a lot of 1x10 groupsets and a very small number of 2x9, but nothing really with a lower number of gears on the cassette.

To my untrained mind, a 1x10 would introduce more stress and flex on the chain than a 2x5 would, especially while riding on the extremes. And, with a 2x5 setup, you could (probably?) have better ratios - I'm thinking it should be possible to set it up in a way where one chainring is better suited for climbing, and the other for higher speeds.

Yet, I don't see any 2x5 or even 2x7 sets out there. What am I missing?

Another question: would it even be feasible to custom-build my own drivetrain with a 5-gear cassette, to use with 2 rings on the front, and if so, how complicated would it be?

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[–] JayleneSlide@lemmy.world 2 points 3 months ago

There are 2x5 components out there. But nobody is really making anything 2x5 because bicycle frames are no longer built with the spacing for the old 2x5 freewheel and hub. Frames of that era were built with 126mm over-locknut dimension (OLD) rear spacing. Then frames went to 130mm, 135mm, 142mm, and up. This is in part to accommodate those enormous cassettes and in part to provide relaxed angles in the rear triangle (more stiffness and strength with less material).

So, parts for those old bikes are the domain of niche designers such as Velo Orange, and NOS experts like Yellow Jersey.

2x5 or even 2x7 sets out there

There are no 5-speed cassettes. That technology started with 7-speed. And you need to have at least 130mm OLD for that technology. There are 5-speed freewheels.There are also plenty of contemporary 7-speed cassettes, shifters and derailleurs, although you will mostly be consigned to friction shifting.

I'm thinking it should be possible to set it up in a way where one chainring is better suited for climbing, and the other for higher speeds

This is the entire design intent behind 2x and 3x drivetrains since the about the mid-70s. I'm hand-waving past some other designs in there, such as half-step. That's a topic for another day.

Another question: would it even be feasible to custom-build my own drivetrain with a 5-gear cassette, to use with 2 rings on the front, and if so, how complicated would it be?

5-speed cassette: no. See above. 2x5/6/7 freewheel? Absolutely. Verify your OLD on that frame. If it's 126mm, you have to go freewheel. If you're 130mm, things get a bit more gray area, because your hub selection goes down. But you can have cassette or freewheel. At 135mm, you got lots more selection, but also can't do any of the 5-speed stuff.

You're wandering into some of the more esoteric and borderline archaeological aspects of wrenching on bikes.😆 There's some base knowledge holes we'll need to fill for your project to continue. There's a lot here, and I'm trying to avoid writing a novella on my phone. So ... what parts of that don't you grok? We can work from there.