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Currently upgrading my old steel mountain bike for commuting. I need some advice on what drive-train to go with. Current setup is 3x7. I will convert to either 1x9 or 1x10 with new rear wheel/hub. I am prepared to pay a bit extra for quality as this is my favorite bike which I enjoy riding. Prices are NZD.

Option 1:

Sram GX 2x10 rear derailleur $143 (Will 2x10 work with my 1x10 setup?)

Sram GX 2x10 X-Actuation trigger shifter $82

any 42 tooth chainring you recommend?

I would like a 11-42 cassette or close to that range, maybe Sunrace MX3? Is it compatible?

Option 2:

Shimano Deore M5120 10/11 speed rear derailleur $100

Shimano Deore M4100 11-42 cassette $89 or Shimano Deore CS-HG500 11-42 Cassette $70

Shimano Deore M5100 2x10/11 speed shifter $49

Option 3: Any Box 9 speed drivetrains, it has 11-46 or 11-50 9 speed cassette options https://boxcomponents.com/collections/prime-9-filter around $449 Long term durability? I'm not too concerned over large jumps with 9 speed 11-46/50 cassettes.

Option 4: https://www.mtbdirect.co.nz/sram-nx-eagle-dub-1x12-groupset Its a 1x12 speed groupset with an 11-50 Sram cassette. It fits 8,9,10 speed hubs. $610

Thank you for any help you can provide me, as you can see I have a few different options and am having a tough time deciding what to go with. I don't want entry level but cannot afford high end so in between is ideal. Thanks again!

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    This is likely to be closed as shopping as well as opinion-based, sorry. Consider Bicycles Chat for a less-rigid structure.
    – Criggie
    Nov 13 '21 at 23:19
  • GX 10 speed is super old. Will be hard to find replacement parts I think.
    – MaplePanda
    Nov 14 '21 at 0:42
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I think a more general question is: what should I consider in converting an older 3x7 mountain bike to 1x9 or 1x10 drivetrain?

Some thoughts:

  1. Old frame's compatibility with bottom bracket for new crank. It's likely your older MTB has an English-threaded BB shell either 68mm or 73mm wide. If so, decent-quality square-taper cartridge BBs are varied and inexpensive. In addition, you could likely use a technically-superior and not much more expensive external-bearing BB such as Shimano's Hollowtech II range. There are many 1x crankset choices which will fit with one of the above BB types.

  2. Old frame's compatibility with new wheel. Your frame probably has 135mm rear dropout spacing ("OLD") and uses 26" wheels. It also likely uses V-brakes rather than disc brakes. Thus, you will need a new 26" rim-brake-compatible wheel with hub matching your new rear cassette. Off the shelf good-quality 26" rim-brake-compatible rear wheels are becoming more scarce these days, so you should consider ordering one from a wheelbuilder.

  3. Availability of older used or "new old stock (NOS)" parts. Older components designed for 1x10 or similar drivetrains when those were current may be cheaper or better-suited than current components (e.g. 1x12 drivetrain components).

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  • Oops, 7-speed hubs are more likely to have 130mm or 126mm OLD than 135mm OLD! So I think the plan won't work unless the frame is steel, in which case it can be cold set.
    – juhist
    Nov 14 '21 at 13:17
  • @juhist You're right that we don't know for sure in this case. From what I've seen, MTBs back to 1990 or so have at least 135mm OLD, but I am not an expert. Also in my experience, 3x7 drivetrains were often used as cost-cutting measures on lower/entry level models long after MTB frames had switched to 135mm OLD.
    – Armand
    Nov 14 '21 at 20:01

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