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I've got a good deal and bought a new bike with full Shimano XT groupset and 2x Drivetrain which I am not fully satisfied with, it has 34/24 and 11-42 setup.

I would prefer 1x more but not going to invest in transformation at the moment.

My question is - as it's not a good general practice to combine lowest-lowest and highest-highest rings (I'm coming from Roadies world), will it be bad to use 34T in front in combination with 42T on rear?

I'd rather not to use the front derailleur at all (would be happier with dropper instead).

swolfish
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    Does this answer your question? Why is cross chaining 'bad', but 1x is OK? and a dozen others covering world ending events caused by cross chaining. – mattnz Jun 08 '20 at 21:44
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    IMO "crosschaining is bad! Don't do it!" is nothing but hysteria and totally irrational. The difference in angle is very small. I've done races with a cassette chosen so that I could stay on the outer chainring the entire race and do all climbs crosschained - with no problems. I've done long training rides with the chain on the inner chainring and have to crosschain on the faster portions - with no problems. Heck, these racing/training techniques were taught to me by some of the better racers on my team. – Andrew Henle Jun 08 '20 at 23:09
  • (cont) The point of staying on the big chainring for a race is to avoid shifting the front - which is when chains get dropped. That even happens to pros in the Tour de France. Leaving the chain on the small ring on a training ride is a good way to keep your power low for long aerobic base rides while forcing you to expand your cadence power band if you really do want to go fast. – Andrew Henle Jun 08 '20 at 23:12
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    What is it about the 2x that you are not satisfied with and what about 1x do you prefer? – mattnz Jun 09 '20 at 07:55
  • @AndrewHenle Yeah, I prefer to stay on big chainring. Rather to wear it little more than change everything. – swolfish Jun 09 '20 at 17:17
  • @mattnz I'm not satisfied 'cause 24T is too small and have no need to use it except on some very steep hills. In my case, 38/28 would fit me much better than 34/24. – swolfish Jun 09 '20 at 17:17

2 Answers2

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The same rules apply to mountain bikes as they do with road bikes when it comes to crosslining the chain. You can agrue it's even more important on mountainbiking as the chain bounces more on rougher terrain.

When you change to a 1x system, the front chainring should have a chainline in between the current 24/34. So the crossline is not as extreme as with 2x systems, when you are at the lowest and highest cogs on the back.

So the answer would be, it's not good practice. But it might be fine. You might experience more chain wear and possibly more chain drops.

To turn into a 1x, all you would need is remove the front shifter, the front mech, the 24/34 chainrings and replace with a 1x narrowwide chainring. Which chainring you need depends on your crankset, the number of gears on the rear, the rear hub spacing.

Also see this disscussion on 1x system crosslining

abdnChap
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    A proper 1x system will use a dedicated 1x crank, that positions the chainring between where the two 2x rings sit (as you said), putting a narrow-wide ring on a 2x crank will create the cross chaining condition that should be avoided. – Argenti Apparatus Jun 08 '20 at 11:21
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    That's not necessarily true, you can get chainrings which conpensate for the chainline difference from a 2x or 3x cransket by being offset – abdnChap Jun 08 '20 at 11:22
  • I always thought those should exist but have never seen them. Can you link to any examples? – Argenti Apparatus Jun 08 '20 at 11:24
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    https://absoluteblack.cc/oval-104bcd-chainring.html – abdnChap Jun 08 '20 at 11:27
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    From the page "important:

    *32T chainring has build-in 2mm spacers and threaded holes (M8x0.75) to accommodate this size on spider. Other sizes have regular 10mm holes.

    *30T chainring has build-in 2.5mm spacers and threaded holes (M8 / M5) to accommodate this size on spider. It also comes with bolts and spacers in the package: 2x M8 aluminium bolts T30 torx, 2x M5 steel bolts T25 torx and 2x eccentric spacers. This is a patent pending solution."

     – abdnChap Jun 08 '20 at 11:28
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    I use the version of the for the XTR m9000 2x crankset. Works no problem. – abdnChap Jun 08 '20 at 11:29
  • Also https://cdn.shopify.com/s/files/1/0230/9291/files/XT_m785_and_SLX_m665_Double_Compatibility_v4.pdf – abdnChap Jun 08 '20 at 11:31
  • '...it's not good practice' is now a controversial statement. – mattnz Jun 08 '20 at 21:49
  • @mattnz Contoversial how? – abdnChap Jun 09 '20 at 08:46
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Definitely get a dropper post, but there's no good reason to get rid of that front derailleur. Don't do it. I've been writing this a couple of times already lately; there seems to be a common misconception around but: 2× is superior to 1×.

What's nice about 1× is that it allows for better rear suspension design (useful in hard-hitting enduro bikes), saves a couple of grams (useful in road racing and cross country) and removes one item that needs maintenance as well as one cable to the handlebars. But I wager that none of this is really very relevant for you, and anyways you wouldn't fully reap the benefits if merely changing a 2× bike to 1×. It's no good just removing the front mech, the chain would jump off way too often, so you would either need to fix it in one position or get a dedicated chain device. (Modern 1× systems prevent this through narrow-wide chanrings, but that requires the entire system to be built for it.) And even then, the design burden that this derailleur brought on your bike is already committed.

On the flip side, 1× requires significantly larger and more disruptive gear jumps, moves more of the weight to the (unsprung!) rear axle, all the while still not offering as big gear-ratio span as a 2× system.

I have an inexpensive Shimano ... think it's also XT with similar specs ... 2×10 on my hardtail, and whenever I ride that bike I'm delighted by the buttery smooth shifts compared to the fancy but clunky 1×12 SRAM Eagle on my Enduro bike.

leftaroundabout
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  • I mean. This is super subjective. – abdnChap Jun 08 '20 at 18:06
  • @abdnChap the only thing that's subjective here is whether you value the æsthetic perks of 1× more than the ergonomic advantages of 2×. – leftaroundabout Jun 09 '20 at 01:29
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    While I agree with the premise that there is no good reason for going 1x and OP is much better investing in a dropper, the answer needs tidy up to remove subjective statements and address several 'statements of fact' that may not be true. (e.g gear range of 10-51 is amply wide enough for a vast majority of riders. Comparing 1x Eagle to 2x XT, then stating the difference is because of the 1x is an argument falacy) to – mattnz Jun 09 '20 at 07:52
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    If you value weight above mechanical benefits, then 1x is superior. If you value ease of maintenance above mechanical benefits, then 1x is superior. Amongst other arguments. So stating the "2x is ubiquitously superior" IS SUBJECTIVE. – abdnChap Jun 09 '20 at 08:43
  • @mattnz I didn't say 1× doesn't offer enough range, I just said it doesn't offer as much as 2× despite using a huge cassette with big gaps. I mean, it's just comparing numerical ratios, how much more objective can it possibly get? (For me personally, the 10-50 of my Eagle is enough, in fact it's about exactly the range I use, but no reserves.) – leftaroundabout Jun 09 '20 at 09:45
  • @abdnChap sounds like you're looking for a fixed-gear track bike. –Seriously though, I did mention weight and maintenance in the answer, so I don't see what you're so upset about. Of course the “superior” statement is opinion, that word is basically almost subjective. But it's an informed opinion based on the objective arguments in the following, and it's directly aimed against the non-informed opinion of many riders currently that 1× is ubiquitously superior just because all better new bikes come with it. – leftaroundabout Jun 09 '20 at 09:54
  • Haha sounds like you're taking this to heart. The OP already states that they want 1x. The question is about cross lining. NOT about what is better. And you do state that it's a "there seems to be a common misconception around but: 2× is superior to 1×" As if it's a final statement without alternatives. Which is obviously not true – abdnChap Jun 09 '20 at 10:06
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    @abdnChap fair enough. But I didn't read the question this way, to me it seemed like the same “oooh, those awesome new bikes all have them shiny 1× systems, that surely means front derailleurs are useless?” I've been seeing so much lately. To which my answer is, no they're not useless, although the reason has little to do with cross-chaining which seemed all the OP was worried about. – leftaroundabout Jun 09 '20 at 10:16