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My daughter was given a 26" hardtail with a slightly weird setup to use as a utility/commuting bike by a guy whose hobby was to build up bikes from old but unused parts... the crankset & mechs are Deore M510 / M590 3x9, but the cassette is a 7-speed, with matching 7-speed shifter & 7-speed chain. I don't know how much difference it makes having the slightly fatter chain on a crankset designed for a 9-speed, but she's definitely never got the hang of a 3x system, crosschains like crazy and doesn't think to change down a chainring 'til she's standing hard on the pedals. The result has been some pretty dramatic failed shifts, jammed chain and broken teeth on the big chainring after about 200-300 miles.

Obviously I could swap to a 9-speed cassette, shifter and chain, replace the big chainring and whatever part of the problem is caused by the mixed system goes away. But I'm thinking this probably leaves the bigger problem, and changing it over to a 1x system might be a good idea.

If I do the latter, I would be thinking to put a narrow-wide chainring of suitable BCD on the middle position of the current triple crankset, remove the other two along with the front mech & shifter, and upgrade the rear mech to a clutched, 11-speed setup to give a very similar range of gears as the current 3x7 setup. It seems like the current FH-M756 hub will work with an 11-speed Shimano MTB cassette, but not 12-speed.

So the questions:

How big an issue is the current mix of 7- and 9- speed bits likely to have been? If I blame that for poor shifting, and believe she'll get the hang of the triple if it works smoothly, fixing the 3x9 saves ~30% compared to a change over to 1x11... the frame is entry-level, so I don't want to spend more than I need to on this bike.

Is there anything else I need to consider in converting to 1x... I assume the middle ring position is the best chainline option?

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    Welcome to the site - Is your daughter still growing? Is this a long-term bike or just enough to get to the next size ?
    – Criggie ♦
    Nov 19 at 23:22
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    This is a great illustration of why 1x makes sense for many cyclists, especially newer ones. I agree with mattnz that it is probably not objectively worth it to convert the bike, though.
    – Weiwen Ng
    Nov 19 at 23:26
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    @Criggie she's pretty much stopped growing - definitely to the point where only minor adjustments in seat height will be needed. I'm thinking she might take the bike to uni in a couple of years as the budget frame branding and unfashionable style might be less appealing to bike thieves who love UK universities, while sorting the drivetrain out should make it a robust and reliable ride.
    – Saes
    Nov 20 at 8:01
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    Although it’s a shopping recommendation, maybe investigate a Microshift 1x9 or 1x8 group. This situation is a great match in terms of need and relative input cost.
    – Warren Burton
    Nov 20 at 8:53
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    @Criggie - bolted
    – Saes
    Nov 20 at 9:47

3 Answers 3

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Cost wise it is probably not a great investment to change the front of the drive train. At some point it becomes a better value proposition to sell the bike and use those funds, plus what it would have cost to upgrade, to invest in a new (to you) bike. If you have a local bike coop could be worth visiting and seeing what they can do to help.

The 7speed chain on a 9speed crankset, being wider, might rub on the front derailleur cage, and might catch the ramps on the chainrings easier, requiring more accurate adjustment, but overall, it should not be a problem. You could try a 9speed chain on the setup if you think the extra width is the problem. Rear shifting might be a little compromised, but it should work OK.

I would suggest leave the front as is. If you get a wide enough range on the rear, she won't ever need to shift the front. If needed, remove the cable from the shifter and set the front derailleur to the middle ring with the L screw (may need a longer L screw, if that does not work, could use a length of shifter cable and barrel adjuster) - effectively 1x'ing the bike without the expense.

On the rear, you probably want to replace everything - decide on the cassette range you need and then the number of gears. 11-36 is common 9speed and will be cost effective if that give the range you need. Realistically the choices from there cannot be dealt with in a Q&A such as this - it is far too broad a problem (What range, how many speed, what brand, what price point).

Cost wise you want to be very careful. You will quickly get into the "it is just a little more to..." (10 speed instead of 9, 11-40 cassette instead of 11-36)

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    Thanks for the considered answer. The cost escalator is definitely something I'm aware of... Or at least thought I was - fixing this bike to stop myself looking at all the options for a replacement :) Since the big ring got mashed and the small ring is ignored she's kind of at your suggestion for the front, but feels the biggest ratio (now 32x11) is too low... I can extend the lower range at the rear, but feel I have to do something to get the top ratio back up, so repairs/changes at the front, lead to thinking about 1x, etc.
    – Saes
    Nov 20 at 9:45
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    32/11 at a cadence of 90 is 30km/h, more than respectable commute speed on a MTB. Is she really needing a larger gear. As her cycling experience improves, she will learn to spin faster (its more efficient than 'mushing' at slow cadence - watch the pros). Consider how often is she topping out, how much enjoyment she loses being topped out, and how much time would it save her? Is it worth the expense?
    – mattnz
    Nov 20 at 19:39
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    I don't disagree. But I know a teenager who does. We've done whole rides discussing the relative merits of all sorts of riding techniques, including immediately prior to the chainring massacre, but sometimes doing it wrong on the bike they will ride is worth a lot more than the better technique on the bike that they won't get out of the shed.
    – Saes
    Nov 20 at 20:26
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    one of the big arguments against 32/11 is how fast it wears out. And the inefficiency of using a chain at an angle so much. Perfect if you only ride off road. 40t is a better consideration for on-road use. @Saes
    – Noise
    Nov 20 at 20:59
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    The compelling argument for 32/11 in this case is that it is much easier to ride the bike you have than the one you want to have.
    – mattnz
    Nov 21 at 22:00
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What I'd do, on a budget, is lock the front mech in the middle ring, disconnect the cable, and fit the widest range 7-speed cassette I could find online (11-32 or 12-34 is common, 11-34 available, 11-36 maybe). That means only buying a cassette.

Slightly more refined would be to do the same but with a 9-speed cassette, shifter, and chain. Then you can get 11-42 which might be out of spec for a typical derailleur.

Given what you say in a couple of the comments, I'd look at replacing the middle ring with a 34 or 36 tooth on the same BCD as well.

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    Shimano now make a derailleur and cassette for 8sp 11-40t. Not expensive parts and solve alot of these questions in the way you describe with minimal investment.
    – Noise
    Nov 20 at 21:02
  • @Noise I didn't think to look for 8-speed, but of course 1 step difference are normally workable. My beater bike near work has a real mess of a setup - a "6 speed" hub, 7 sprockets of an 8 speed cassette, and the 2 smallest off a 9-speed, all with an 8-speed shifter. Works pretty well for a quick bodge,but I avoid the smallest sprocket as it doesn't engage the splines properly
    – Chris H
    Nov 20 at 21:05
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    Depending on the 7sp shifter, some of them can be converted to 8. Save a penny!
    – Noise
    Nov 20 at 21:09
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A 7 speed cassette is a rare thing now days. I use them on my wet-day road bike and no bike shop stocks them. Check its not a 7 speed freewheel instead of a cassette.

A 6, 7, and an 8 speed cassette all use about the same width of chain. They get more gears in the cassette by being wider but the cogs have the same spacing. So a 7 speed wheel might only take a 7 speed cassette, or it might have some spacers stacked up behind the 7 speed cassette (hopefully this!)

I'd check first that the rear wheel can take an 8/9/10 speed cassette and have the lockring engage securely before you start contemplating upgrades. Any 8/9/10 speed cassette will do for a test - you're not actually riding on it.

The crankset generally won't really care about the chain width - I have a triple crankset for a 5 speed rear, that works fine with 9 speed chain. So, if you can get a narrow-wide chainring that fits the middle spider mounts and has the same BCD, then you're good.

Optionally, use the limit screws to lock the front derailleur in place on the middle, and potentially remove the front cable and left-hand shifter.

In the end, there's a good chance this bike will get stolen or similar especially if it has to be parked/locked outside. Don't spend excessive money on it, and consider whether you'd even claim insurance if it was lost.

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    Thanks - definitely a cassette on a hub that the Shimano website says can go up to 11 speed. As I say, it's a bit of a weird mix of parts!
    – Saes
    Nov 20 at 11:16
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    @Saes I predict there are multiple spacers under the cassette. That gives you a lot of options - if the hub was 7 speed wide, then it would require a new hub or new rear wheel too.
    – Criggie ♦
    Nov 20 at 19:48

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