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The drivetrain of my trekking bike ( http://archive.breezerbikes.com/2017/Breezer/liberty-3r3 ) has worn down and is finally in need of replacement. I was wondering if it would make sense and be possible to convert my current 3x9 gearing to a single chain ring and an 11-speed cassette. I would like to keep using Shimano, but SRAM would be an option too as I heard. In any case, if someone has a recommendation for a 1x11 group set that would fit with the frame bearings and would be a small upgrade from Altus/Deore it would be much obliged.

Current group set:

  • Front Derailleur - Shimano Altus 9-Speed, 34.9mm
  • Rear Derailleur - Shimano Deore 9-Speed, SGS, Shadow Design
  • Shifters - Shimano Altus 27-Speed (3x9)
  • Cassette - Shimano HG-300 9-Speed, 11-32T
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  • What is the problem you're trying to solve with this 'upgrade'? Sep 5 at 16:47

2 Answers 2

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TLDR: it is straightforward if you consider that not having the ratios that you currently have on the largest chairing is fine. If you like to keep the ratios that you have on the largest chainring, it's doable with some cranksets with removable chainrings.

It's something I keep investing but there no simple answer yet. Trekking components are "based" on MTB standards, but have diverged recently. MTB have been going to single chainrings and large cassettes, trekking remain almost unchanged. Also, the use of cassettes with 10T sprockets has allowed to shrink the chainring size. Trekking groupsets have ratios that are closer to gravel bikes, but gravel groupsets are not usable on trekking bikes, because bottom brackets have different widths.

If you prefer to keep your current wheels (if you still have the stock wheels, it's very unlikely that you can just swap the freehub body, so you'll need a new freehub, replacing the whole wheel makes more economical sense that just replacing the hub) and still have high ratios, you will basically need a 40T or 42T chainring (the ratio will still be lower than what you have now, but that's not a bad thing). But on MTBs, mainstream brands are selling 36T at most (sometimes 38T, but you'll find them in catalogs but not in stores).

I haven't found at this stage a modern crankset with a 40T-42T that would work with a 73mm bottom bracket. Even exotic cranks like garbaruk are not selling chainrings that would fit on MTB cranksets with more than 38T. But if you bike has removable chainrings, you can probably order a compatible chainring at garbaruk. Make also sure that you can fit a larger chainring at the position of the middle one.

That being said, what I wrote is valid only if you want to keep "gravel ratios". If you are OK with the compromise of having smaller ratios, the most straightforward option is a 36T MTB cranksets, then standard MTB derailleur at the rear, but with a cassette that has a 11T smaller sprocket. If you enjoy riding without the large chainring, that will work.

Recommendation are usually not appreciated, because they are only valid at one point in time. In "deore price points", SRAM seems to have a bad reputation (no personal experience). A Deore M5100 (11-speed) would be highly recommendable. Or a M6100 with a non Shimano cassette (because of the 11T sprocket).

Note that 73mm bottom brackets are arriving on gravel bikes. But now, it's still problematic: only SRAM does it, but compatibility is an issue.

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Another thing to be aware of when going from 3x9 to 1x11:

It's not just about the top and bottom gears - the jumps between all the available gears in between can matter too.

You will lose a lot of gears. And that might matter, especially for a trekking bike if you're hauling gear on long rides.

If you like pedaling at 85 to 90 RPM for a long climb, it's usually not hard to find a gear that would allow something in that range when you have a 3x9 setup. With a 1x11 you will find yourself in situations where you can't ride at your preferred cadence because a wide range cassette must have relatively large jumps between gears in order to get that wide range.

A 1x11 will have gearing something like 11-13-15-19-21-24-28-32-37-42. The jumps in gearing there average about 15% or so with larger jumps towards either end, so if you like spinning away at 90 RPM, you might find yourself in a situation where you have to choose between low 80s or high 90s if you want to maintain the same power or speed in your climb.

Just something to be aware of.

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  • I disagree that you lose a lot of gears switching to 1x, wide range systems. You lose several redundant gears, and a couple of useful gears.
    – Paul H
    Sep 5 at 14:00
  • @PaulH A 53/42/30 crankset and an 11-12-14-16-18-21-24-28-32 cassette gives 27 gears. Per sheldonbrown.com/gear-calc.html, in gear-inches and sorted from smallest to largest, they are 25.3, 28.9, 33.8, 35.4, 38.6, 40.5, 44.7, 45.0, 47.3, 50.6, 51.1, 54.0, 57.9, 59.6, 63.0, 67.5, 68.1, 70.9, 73.6, 79.5, 81.0, 89.4, 94.5, 102.2, 103.1, 119.3, and 130.1. You have to really expand any definition of redundant gearing to even get close to 10 redundant gears - IMO there are 22 useful distinct gears there. So you're probably going to be losing 10+ useful gears. Sep 5 at 14:17

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