Hello all
I'm (still) re-building my old 26" wheel bikes and last year I grabbed a good deal on a Shimano XT FC-M8000 2-ring (36-26) crankset on ebay. After much stalling and consideration, I am now persuaded by this modern concept of going single-ring on the front.
1) Am I able to convert this 2-ring FC-M8000-2 ( https://bike.shimano.com/en-EU/product/component/deorext-m8000/FC-M8000-2.html) to single-ring? By this I mean if neither the 26/36 rings on there at the moment feel right, could I get a 30/32/34 CRM81 ( https://bike.shimano.com/en-EU/product/component/deorext-m8000/SM-CRM81.html) and just bolt it on instead? Or can I only use those separate chainrings with the single-chainring FC-M8000-1?
The chainrings are just bolted on to the arms so I _assume_ a new CRM81 ring of appropriate size could just be added onto the arms instead:
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2) My cassette is 11 speed 11t-42t so what sort of single chainring size should I be looking at with 26" wheels? This first bike will be mostly used for hacking around town, bridle-way mincing and some non-technical fireroad/woodland blasting... all mostly on the level. I appreciate gearing ratios are highly subjective, which is why I'm going to give it a go with the 26/36 chainrings I have first.
Cheers, B
You should be able to put a single ring on that, it doesn't have to be a shimano ring just one with the holes in the right places. The key measurement is the BCD (bolt circle diameter). I'd imagine somewhere in the 32-36t range depending on fitness, local hills etc. Make sure you get a narrow wide ring though as this will help the chain stay on.
The M8000 crank arms are the same for 2x and 1x so the CRM81 will fit just fine. You might find that longer bolts and some chainring spacers can help with the chain line - putting the single ring somewhere between the inner and outer positions.
Here's the exploded diagram with part numbers for bolts. I was looking at it this morning as a mate is planning on converting to 1x on his bike and running a CRM81 ring.
This is great info - thanks all.
Doh - I absolutely should have checked the exploded views.
I was assuming/hoping that these crank arms were basically the same between the 1x11 and 2x11 models. However in my research over the last few months of modern (anything more recent than ~2010) MTB trends then all bets are off as far as which components can be swapped around. My recent discovery this weekend was that the fluid reservoir of my new Shimano M8100 brakes stops them being mounted next to my old XT 9s shifter as it obstructs the top trigger.
These XT cranks are well over-spec for this clunky old daily-grinder hardtail re-build, so I'll eventually swap them on to my LTS re-build once I get the shock and pivots cleaned-up.
I am a noob when it comes to estimating gear ranges, since my last drivetrain shopping was about 20 years ago (eek!) but with the help of https://howto.bike/gears/ I have been able to get a good idea of how a 1x11 or 2x11 would compare to my old 3x9 and I reckon a 34 size is probably my sweet-spot for a 1x11. Since I'll probably be running this hardtail more on road/gravel then having emphasis on top speed rather than granny-ring-style grinding makes sense.
Cheers, B