I'm looking to convert a 1x10 Mtb of mine into to a 2x10.

The gear ratio im intent on is 36/24 with an 11-40 cassette. I owned another bike years ago with this gearing and im looking to replicate it as I really enjoyed the spread. It was great for touring up climbs and had juuuust enough tallish gears for the type of descending I'll be doing. The rear mech was 2x10 sram GX, but im open to others.

Ive built several bikes over the last 4 years, but they've all been 1x, or road doubles. So I really dont know much about the older mountain double world and ive been having trouble finding reliable information which coordinates with products still available today.

This project doesn't need to be low budget, I'd be willing to spend what I need to get some longer lasting parts if anyone has strong feelings. This project is for purposes of remote dirt touring, so reliability + compatibility are my priority.

If I can't find a 36/24, Im willing to get a 36/26 assuming the crankset is available with a 24t ring I could purchase separately. Ive been struggling to confirm compatibility for this online.

The frame im working with is a 2019 Niner Sir9 which ( according to niner) will work with a double. Its boost spacing.

The BB on this Sir9 frame is press fit, so a 2 piece crank would be ideal, but I believe I could also run a wheels MFG adapter to enable a square taper if I needed to. Im currently running a wheels MFG sram dub adapter and its been problem free for years now.

I dont have weight concerns but im always willing to pay more for something a little lighter.

If anyone can recommend a 36t Mountain double crankset that has compatibility with a 24t small ring and a reliable double 2x10 group for a flat bar id appreciate it. I like 2x10 for this project, I'd like to avoid going 11 speed.

I've been considering running friction thumbies which would probably open options up even further, but I haven't decided if I want to do that just yet.

Thanks in advance.

PS - where do people put the dropper post lever on a double?

2 Answers 2


I want to avoid product recommendations as these are off topic. Could be worth looking at Microshift for this project.

First problem to solve is the front derailleur mount and cable routing - do you mind the cosmetics of running full length outer and 'cable ties'?

Standard MTB 2x use a 104/64 BCD - you will be able to go down to as small as a 22 ring if you want on any crank.

10 speed Boost spacing cranks in 2x is still available (e.g. Shimano Deore), but not in top end lineups. You may be able to pick up older XT in 2X boost.

Dropper post you have a couple of options - old school - droppers were popular before 1x, original levers were designed to sit beside the shifters. You can still get these as after market, or some posts come with an option if supplied with an 'under grip' lever. An option to consider is a grip shifter for the front derailleur.

  • Right on. Thanks! Yes the frame has external cable routing. Good to know about older droppers. I'm thinking I might go with Sram GX 2x10. It's still available and it's very affordable. I've owned Sram GX 1x12 kit, and it was plenty durable. So im hoping the older sram GX 2x10 stuff is also. Commented Oct 21, 2023 at 1:15

172.5 cranks are almost totally in the realm of Road.

It is possible to put together a fully compatible system with everything you desire but I only know one manufacturer that has the goods. Therefore this is somewhat like a product recommendation but is really an example of how I would achieve your request.

Middleburn in the uk produce a chainset system that can be used to make up your ratios in the required crank length. You could select the road RO2 crank arms but specify a spindle length appropriate for your mountain BB (which will be 5mm+ longer than road generally), then select the spider that works with the two rings you want to use and gives appropriate chainline. It's some work, but you end up with exactly what you want.

The other routes I can think of involve some level of compromise but there are a couple of other posibilities.

  • Thanks for the response. the crank arm length isn't a big priority. I probably should have left that out. Im pretty used to 175 on my current 1x MTB crankset. Good to know about middle burn though. Commented Oct 21, 2023 at 1:18

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