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Swapping Cranksets - compatibility and chain length

dee4life2005dee4life2005 Posts: 773
edited February 2018 in Workshop
I have three bikes with Ultegra 6800 ... a CX bike with 46/36, a road bike with 50/34 and a road bike with 52/36.

My commute is largely flat, so I was planning on swapping the older road bike to 53/39 ... and having this gear combo would then give me three options across the two road bikes.

What I'm wondering is ... would the road cranksets work on my CX bike as well (Cube Cross Race Disc Pro - if it makes a difference) ? I tried searching google for hours for an answer but couldn't come up with anything.

Also, does anyone know how many links I'd likely need to add when switching from 50/34 to 53/39 (11/28 cog at rear).

Ta.

Posts

  • The RookieThe Rookie Posts: 27,802
    Links first, if the chain is currently set spot on you will need to add 1 pair of links (53-50 is 3, but the chain only wraps round half the chainwheel so that is 1.5, round up to 2).

    As for fitting the the 53/39 on the older bike, well it will probably be fine, just make sure there is enough space as some bikes flare the chainstays a bit close to the rings (or just 'behind' them), easy enough to tell by eye.
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • milemuncher1milemuncher1 Posts: 1,472
    The 53-39 with an 11-28 combo will be just fine with a 114 link chain ( it’s what I use on my 6800 equipped bike with that combo). As long as the CX bike has the correct spindle diameter / BB for the Chainset you want to use, there’s no problem with swapping to a bigger Chainset, as long as your rear mech cage is long enough / has the capacity it needs, to cope with the the bigger chainrings, adding to the chain ring / cassette sprocket difference. If you’re going to a bigger Chainset, you’ll almost definitely need to raise the front mech up a bit, you may not have enough cable to do so, and if not, you’ll have to get a new inner cable ( preferably inner and outer ) for the front mech.
  • Thanks for answers.

    I have been sizing my chains spot on, so I was expecting to have to lengthen - just didn't know by how much, so wanted to be sure the new chains I have in the shed were long enough (114links). Nothing worse than buying new kit and then realising you'd overlooked something and had to wait on another component before being able to ride it. (already have spare cables).

    Had completely forgotten to consider the possibility that the chainstay design may cause an issue. The PlanetX Pro Carbon does have fairly flared chainstays, but I think they start to flare out far enough from the bottom bracket area to allow the chainset to fit without interference.

    The only chainset I'd planned to swap to the CX was the 50/34, to give me a slightly lower bottom gear for the winter - as the bike gets rather heavy and sluggish going up hill with all the extra clothing and Marathon Winter tyres. Tend to only use it on road in winter so the 50T instead of 46T big ring isn't so much of an issue there, and would come in handy for the rare occasion the 30+mph wind is at my back instead of in my face, lol.

    Will need to check spindle length is compatible then ...
  • milemuncher1milemuncher1 Posts: 1,472
    Thanks for answers.

    I have been sizing my chains spot on, so I was expecting to have to lengthen - just didn't know by how much, so wanted to be sure the new chains I have in the shed were long enough (114links). Nothing worse than buying new kit and then realising you'd overlooked something and had to wait on another component before being able to ride it. (already have spare cables).

    Had completely forgotten to consider the possibility that the chainstay design may cause an issue. The PlanetX Pro Carbon does have fairly flared chainstays, but I think they start to flare out far enough from the bottom bracket area to allow the chainset to fit without interference.

    The only chainset I'd planned to swap to the CX was the 50/34, to give me a slightly lower bottom gear for the winter - as the bike gets rather heavy and sluggish going up hill with all the extra clothing and Marathon Winter tyres. Tend to only use it on road in winter so the 50T instead of 46T big ring isn't so much of an issue there, and would come in handy for the rare occasion the 30+mph wind is at my back instead of in my face, lol.

    Will need to check spindle length is compatible then ...

    Sounds like you’ve got it sorted. As you’ve said, make sure your spindle diameter is compatible ( a PF 30 BB is no good for a Hollowtech 2 Crank, for example, without reducer shims). And make sure that your B.B. shell is wide enough / not too wide for your chosen Crank set.
  • imposter2.0imposter2.0 Posts: 11,964
    Let's not confuse things with talk of spindle diameters or PF30 reducers. If all three of your bikes are fitted with 6800 HT2 chainsets, then they will all be interchangeable. Simple as that.
  • All three bikes have ultegra 6800 hollowtech2 chainsets ... although the CX one is a slightly different design for 46T outer ring.

    Two of the bikes (The CX and PlanetX) have SM-BBR60 bottom bracket with external cups - but my more expensive Giant has a BB-71 press-fit - same internal spindle diameter of 24mm though.

    Looks like I should be good to swap at will, just taking into account the chainlength and moving the front derailleur up/down as needed.

    Thanks for the help.
  • milemuncher1milemuncher1 Posts: 1,472
    All three bikes have ultegra 6800 hollowtech2 chainsets ... although the CX one is a slightly different design for 46T outer ring.

    Two of the bikes (The CX and PlanetX) have SM-BBR60 bottom bracket with external cups - but my more expensive Giant has a BB-71 press-fit - same internal spindle diameter of 24mm though.

    Looks like I should be good to swap at will, just taking into account the chainlength and moving the front derailleur up/down as needed.

    Thanks for the help.

    That should work fine.
  • cyclecliniccycleclinic Posts: 6,865
    going from 50T to 52T chainring add 0.5" to your chain length or half a full link. you cant add that so if your mech is stretching alot in big big then fit a new chain. If not then you will be o.k.

    Each tooth tot the cassette or the chainring add ~0.25" to chain length. So rookie your advise is incorrect about the chain length
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • cooldadcooldad Posts: 32,599
    I would still always measure a new chain properly rather than counting links.
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  • cooldad wrote:
    I would still always measure a new chain properly rather than counting links.

    True, that’s always prudent.
  • Turns out the chain was ready for a change anyway, just dropping into the 1.0 on the chain guage. The bottom bracket had also gone with the bearings shot on both sides ... how I didn't notice that before I don't know - the constant mud-splatter, desite daily cleaning, must have been masking the noise.

    Took the opportunity and replaced the BB, and fitted a new chain which I sized properly ... checked the chain line after linked and fed through the rear derailleur and spot on. Shifting sweet on the new 53/39T set up. Didn't even need to swap out the front derailleur cable, as there was just enough tail to use, and no fraying ... so I just re-clamped it in the new position, after moving the front derailleur up to its new higher position on the seat tube.

    Result.
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