this post was submitted on 18 Apr 2025
8 points (83.3% liked)

bike wrench

1004 readers
1 users here now

A place to ask bicycle repair questions, and for bike shop monkeys to share advanced non commercial wrenching resources (no YouTube self promotion). This is only for repair related topics.

!bicycles@lemmy.ca

!micromobility@lemmy.world

founded 2 years ago
MODERATORS
j4k3@lemmy.world
8
why aren't there any 2x5 groupsets? (slrpnk.net)
submitted 2 months ago by vomitaur@slrpnk.net to c/bikewrench@lemmy.world
15 comments fedilink hide all child comments
 

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?

top 15 comments
sorted by: hot top controversial new old
[–] litchralee@sh.itjust.works 7 points 2 months ago (1 children)

From a complexity perspective, a 1x10 setup has fewer moving parts than a 2x5 setup, due to not needing a front deraileur, its cables, its shifter, and its rubbing surfaces against the chain. Yes, a 10-speed chain might be narrower and thus have to be stronger for the same loads, but roller chains are already very robust compared to finicky derailleurs in normal service. What sort of "riding on the extremes" do you plan for this commuter bike?

From a ratios perspective, a 1x10 gives you 10 non-overlapping ratios. Whereas a 2x5 is likely to have some ratios that overlap, unless the two sprockets in front are absurdly wide, at which point there's a concern if it can shift reliably.

There may be other reasons, but those are the two that immediately came to mind.

[–] vomitaur@slrpnk.net 2 points 2 months ago (1 children)

that makes a lot of sense, thanks for explaining it so well!

riding the extremes

by that i meant on the lowest gear and highest chainring, for example. my rockhopper has the original biopace on it, 3x7, and the chainrings are warped; when I'm on the outermost ring and almost any of the gears, it always rubs somewhere, and I can practically feel the chain flexing.

[–] litchralee@sh.itjust.works 1 points 2 months ago* (last edited 2 months ago)

Ah, I see what you mean now.

I am not an expert at building or specifying whole bikes from the frame up -- though I have built wheels before -- but my understanding is that provided that the rear cassette, the chain, and the front sprocket are all compatible w.r.t. teeth width and spacing, and there is adequate clearance for both derailleurs from the frame and to the ground, I can't see why you'd be prevented from fitting a 2x5 or 2x7 setup into the space where a 3x7 used to be.

That said, when it comes to replacing non-like-for-like parts, you'll have to consider what your design priorities are. For example, would you want to keep the same "width" of ratios as you had with the old 3x7. That is to say, the final crank-to-wheel ratio in the new lowest and highest sprocket combinations would roughly match that of the existing sprockets.

I'm not entirely sure what style of bike a Rockhopper is, but the name suggests it might be geared like a mountain bike, so possibly lower ratios than a commuter might have. Then again, maybe you prefer a faster crank cadence and are fine with that ratio at higher speeds.

You should take time to evaluate what exactly you want from your drivetrain, and that will indicate what you would replace those components with. If you can find modern bikes with something similar to your wants, that would also work as a reference (eg parts, ratios, etc).

For example, I personally find that my 3x8 acoustic bike realistically could have been a 1x6, because I basically always leave it in the 2nd front sprocket and use only the even numbered rear sprockets, except for substantial grades that need the largest front sprocket.

Alternatively, for my Class 3 mid-drive ebike which is configured with a 1x9, I also only use every even sprocket, because the motor has a fixed cut-out time for every shift, so I might as well shift two sprockets at a time when accelerating from a stop.

I can practically feel the chain flexing

Supposing you were able to fit a 1x10 into your existing frame -- and it might not be possible unless you have a new rear wheel with a narrower hub -- the driveline could theoretically -- I'm guessing -- be optimized to prefer either the higher or lower ratios. In that way, you could minimize chain flex when in the most common ratio, although I wouldn't necessarily obsess about this too much unless you find proof that it's actually wearing away your chain or sprockets faster than expected.

Basically, sketch out a design, try it out, and let us know how it goes!

[–] jrwperformance@lemmy.world 6 points 2 months ago (1 children)

Theres a benefit gained from ditching the front derailer. One-by systems use a narrow wide chainring on the crank to better hold the chain. Paired up with a clutch in the derailer, you'll never have the chain come off in rough riding.

I'm a large (6'4" and 280lbs) and pretty powerful rider and my 12 speed Sram/Shimano systems hold up very well.

[–] JayleneSlide@lemmy.world 1 points 2 months ago (1 children)

12-speed generally can't fit in an old bike spaced at 135mm OLD + QR rear fork ends. There might be an HG-11 hub such as the Halo Retro that might do the trick, but that's getting into bike arcana and some dark spells.

[–] jrwperformance@lemmy.world 2 points 2 months ago (1 children)

The 12 speed was mostly an example to say it's a durable system. I also have a Resto-Modded Schwinn road bike from the 80's with a modern 11 speed Shimano set up.

[–] JayleneSlide@lemmy.world 1 points 2 months ago* (last edited 2 months ago)

Restomod, you say? I have such a nerd-boner for modernizing old school bikes. Tell us more! Can we see a pic?

I was given an 83 Rodriguez last summer, and the last of the parts for that rebuild arrived yesterday. So excited for that build. I just need to figure out which beer goes with the build.

[–] Showroom7561@lemmy.ca 3 points 2 months ago

Overlap, and large jumps between gears would make a 2 x 5 feel awful.

[–] JayleneSlide@lemmy.world 2 points 2 months ago (2 children)

I debated editing my comment for some additional resources, but decided that a separate comment might be better.

If you're just starting out wrenching on your own bikes, the late, great Sheldon Brown is a fount of knowledge and wisdom that we can all aspire to be: https://sheldonbrown.com/

Velo Orange is a great source for the intersection of retrogrouch and modern hotness to keep your old bike running: https://velo-orange.com/

Rivendell is the original retrogrouch bike company: https://www.rivbike.com/

Yellow Jersey for all your NOS needs (antediluvian website warning): https://www.yellowjersey.org/

Modern freewheels from one of my favorite LBS, which just happens to have a strong internet presence: https://www.universalcycles.com/shopping/index.php?category=1665

You're going to have trouble finding chainrings for 5-speed. If you're willing to deal with a reduced shifting experience, you can go with chainrings designed for single-speed. The ring is has teeth that are unprofiled, and there is no contour or shifting ramps. This is what I do with the middle ring on my 3x9 setups. Since I'm almost always in the middle ring, the beefier middle ring needs replacement far less. And secret pro-tip: monitor your chain wear, and replace your chain well before it reaches 100%. The rest of your drivetrain will last much, much longer.

If you have 130mm or 135mm spacing, check out Microshift Sword Black. Yes, it's 9-speed, but you can get a proper gear range with that. Also, Shimano CUES Linkglide might have a combo that can work for your bike.

[–] vomitaur@slrpnk.net 2 points 2 months ago

thanks for the extra extra. I've been cycling for my whole life, and have always done the basic maintenance myself. only recently have i felt like tackling the stuff i used to leave to the LBS.

it's got 135mm, so i'm sure i can fit a 9-speed cassette, i've been biasing more and more to a 1x9 since reading your other comment - the end goal of this rebuild is a commuter, and my route is fairly flat and asphalt, so I don't need a lot of range in the gearing. what's currently on it is a 3x7, and I'm in the middle ring most of the time as well.

thanks again, i'll check those resources out

[–] limelight79@lemm.ee 2 points 2 months ago (1 children)

I love how much Velo Orange is getting mentioned in these comments. I built a gravel bike out of a Velo Orange Pass Hunter frame a little over a year ago.

But I used a Di2 group because that's what I wanted. Blasphemy, I know.

[–] JayleneSlide@lemmy.world 2 points 2 months ago* (last edited 2 months ago) (1 children)

I used a Di2 group because that’s what I wanted. Blasphemy, I know.

Nah, no blasphemy in sight. I think Di2 is pretty amazing. Electronic shifting eliminates so many issues inherent to high gear count, cable-actuated shifting. It's not for me and the way I ride, but the reasons for its popularity are plain as day.

Edit to add: built up a 1st gen disc Pass Hunter, which I very stupidly sold because I didn't ride it for a year. Live and learn.

[–] limelight79@lemm.ee 2 points 2 months ago* (last edited 2 months ago) (1 children)

Heh. I converted my CAAD12 to Di2 last year, but then I bought a used Supersix Evo that again has mechanical shifting (albeit with hydraulic disc brakes, not rim brakes like my CAAD12). I miss the electronic shifting, though I will admit that group does work pretty well. But the Di2 is still better, and I miss the buttons in the hood for controlling the computer. I intend to upgrade that bike to Di2, maybe over the winter.

No regrets on my gravel bike, but I also haven't taken it on any tours.

What bag is that?

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

The bag is a Carradice Nelson Longflap, mounted on a Bagman QR Expedition rack. In that pic, it's about 12 years old and is now 22 years old. Still going strong. The transverse saddle bag is my preferred carry method for everything other than self-supported loaded touring.

The longflap aspect of the bag lets you do some ridiculous stuff.

[–] JayleneSlide@lemmy.world 2 points 2 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.