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I currently have a Shimano drive-train and am approaching replacement for the chain and cassette. All parts are Deore XT M780 Series except my cassette which is a HG500-10 11-25 I usually run a Shimano chain to match, although right now I have a Taya e-DECA-101 which I am not to happy with so will go back to something like the XT CN-HG95. Crank-set is a FC T871 - 170mm 48-36-26 and mech is a RD T780.

Most of my riding is commuting ( 15 KM each way ) and non competitive leisure/exercise rides ( <100KM ) on relative flat ground. For how I use my bike the 26 ring is pretty much useless and the 36 is only marginally useful. I am almost always on the 48 and the rear is usually on one of the top 4 sprockets. Given all this I have been looking for option to lift the range at the top end and perhaps make the smaller front rings more useful. Searching I find references to a Shimano 105 Triple 30/42/52t crank-set but am not knowledgeable enough to know if this is compatible.

I am open to changing to a two ring setup and changing shifters but have flat bars so seem to have limited option there even if I can find a compatible crank-set set.

I guess my question is whether the 105 crank-set is compatible with my the rest of drive-chain, if not do I have any other options ?

EDIT: I should mention that I ride a trekking bike not a mountain bike and almost exclusively on paved surfaces.

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  • Being Deore XT, you're probably on an MTB, so while "might" work I would rule out 105 which is a road group set. Also considering that your primary use is commuting, would consider XT pretty over the top. Perhaps you might be better off looking a Deore (Non XT) or CUES group set. Would think if Cassette & chain are due replacement, then possibly Chain rings are due, maybe chance to go for 1x with larger chain ring?
    – Hursey
    Commented Jul 26, 2023 at 4:56
  • @Hursey Thanks for the input but I have a trekking bike not on a MTB. The XT was what came with the bike and I find it performance to be excellent. Looking at Deore and CUES neither seem to have any option with larger chain rings and switching to a 1x with a smaller ring would be a step away from what I try to achieve.
    – Domoninic
    Commented Jul 26, 2023 at 11:58
  • More accurately, you are on a bike that uses MTB style cranks. These are wider than road cranks.
    – Weiwen Ng
    Commented Jul 26, 2023 at 12:41
  • @Hursey I don't really see why XT would be "over the top" for a commuter - if the commuter is not a beater bike, obviously. Maybe the ratio durability/price is not the best for consumables, but you can use a Deore chain/cassette on an bike having XT. Derailleurs and shifters last very long and are nicer to operate (and remain nice to operate over time), so I don't see a reason to "downgrade" because the bike is used to commute. My only reserve (my commuter has a 1x12 XT), is about the cassette - when commuting, I use the smaller half, but I can in fact buy the small sprockets separately).
    – Rеnаud
    Commented Jul 26, 2023 at 12:59
  • @Renaud, wasn't meaning ditch XT and throw it away, just suggesting that if replacing parts there are cheaper options. Being a commuter, I wouldn't expect there being any real noticeable gain going XT over cheaper group sets. In no way meaning shouldn't use XT if that what you like
    – Hursey
    Commented Jul 26, 2023 at 20:39

2 Answers 2

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To fit a road crankset on a trekking bike, I'd see two potential blocking points:

  • the bottom brackets. Trekking bikes components derive from MTB standards, that require 73mm bottom brackets (part on which the bottom bracket is mounted). But trekking bikes can have 68mm shells (standard width for road), and in that case they use MTB bottom brackets with spacers to account for the shell width difference. If the shell is 68mm wide, you can get to next step, if it's 73mm, the 105 crankest won't be compatible.
  • frame clearance: space between the chainrings and the frame to fit larger chainrings? If yes, then the 105 derailleur could fit on the bike. You'll need to change the bottom bracket and the possibly the front derailleur as well (the shape of the cage depends on the chainring sizes) — take into account that road chainrings are bigger and closer to the frame.

Note that the trend now on higher cadences (pedaling faster with less effort), so it's very hard to find non-road chainrings bigger than 48T (and even 36T in simple chainrings).

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    Thanks for the informative reply. For reference this is my Bottom Bracket and Crankset Looking at my Bottom bracket there appears to be two spacers about 2.5 mm thick on each side. It looks like the shell is 68 mm so onto the second part... I am pretty sure frame clearance is good but will do a little more research there. Provide that is all Ok then I will would also need a bottom bracket to suit the 105 crank. Assuming that is all possible do I need worry about my shifters or are 10 speed Shimano cross compatible ?
    – Domoninic
    Commented Jul 26, 2023 at 18:58
  • @fatoms so indeed a road bottom bracket would be required. As far as I know, pull ratios are the same between road and MTBs for front derailleurs, so your shifter should work... but I just remember that road shifters (the integrated ones at least) have a feature called "trimming" (moving the front derailleur a bit less that half a shift) to avoid chain rubbing. Not sure that "road shifter for flat bars" have it, it might be worth asking a new question for that.
    – Rеnаud
    Commented Jul 27, 2023 at 6:43
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It looks like the M780 crank takes standard 104mm 4-bolt chainrings, so in my opinion the best solution would be replacing just middle and large rings with larger ones. There are third party manufacturers such as Specialites TA that make a full range of replacement chainrings up to 50 teeth.

As explained in the other answer, replacing a MTB crankset with road one can run into clearance and alignment problems.

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