53/34 chainrings??

dubbs2009
dubbs2009 Posts: 310
edited September 2014 in Workshop
Any advice on whether changing the small chainring on my standard cranks (e.g. 39T) to a compact (e.g. 34T) will be a good idea / work well without needing new mechs/chain etc?

Comments

  • majormantra
    majormantra Posts: 2,094
    If your cranks are 130mm BCD then you won't able to go below a 38t.

    Also, a 53/34 would probably shift really badly and might well exceed the capacity of your rear mech.
  • dubbs2009
    dubbs2009 Posts: 310
    OK thanks - thought it would probs be a bad idea... just mulling things over in my head...
  • marcusjb
    marcusjb Posts: 2,412
    Major Mantra has it right - you need a compact crank to fit a 34T inner ring on. You can get large outers that will fit on a 110mm BCD compact crankset, so you could have a 53/34 setup in theory (but if you are able to push a 53T, you shouldn't be needing a 34T to climb!). But yes, you'd be way beyond the specification of the front mech (16T on most Shimano front mechs). You could maybe mess around with using a triple front mech with bigger capacity. Might work.

    But then you'd have to look at the capacity of the rear mech.
    Stuff about riding a bike a long way
  • majormantra
    majormantra Posts: 2,094
    Indeed, I should have said the capacity of both mechs. The rear is more often overlooked.
  • marcusjb
    marcusjb Posts: 2,412
    MajorMantra wrote:
    Indeed, I should have said the capacity of both mechs. The rear is more often overlooked.

    Don't worry, I wasn't having a go - both mechs would have to be run (roughly) within capacity - but the front mech in this case wouldn't be able to handle the vertical difference between 34 and 53. I reckon a triple mech could work - but it would probably be a right faff to get it setup correctly.

    If the OP is a strong rider who can make the most of a 53, they really shouldn't need to be looking at a 34 inner as a generalisation. Swap the whole crankset for a 50/34 compact if you are really needing that 34. Most riders won't spin out a 50/11 on anything other than big descents, so it's not a big deal to lose the 53 to gain the 34.
    Stuff about riding a bike a long way
  • cycleclinic
    cycleclinic Posts: 6,865
    If you are strong enough of a 53T you can handle a 39T inner.
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • dubbs2009
    dubbs2009 Posts: 310
    Thanks guys - the 53/39T chainset was what came on the winter bike I purchased - was a good deal on a lovely bike so I was not too worried about the standard cranks vs compact - not taken it out on the hilly terrain of the Cotswolds yet - but turboed on it last night and with the TT on full resistance spinning in 4th gear at 90rpm was 16.5mph so the lowest gearing of 39T / 23T (as per current setup) is gonna be a killer on the 20% grad hills round here... I am gonna stick a 12-27T cassette on and see how that works out... if it proves to much pain for not enough gain then will change the cranks to compact. If I do change the cranks will I need a new front mech? I would imagine it will need moving down on the tube yeh?
  • keef66
    keef66 Posts: 13,123
    "I would imagine it will need moving down on the tube yeh?"

    Yes, so the front mech cage clears the teeth on the large chainring by 1-2mm
  • dubbs2009
    dubbs2009 Posts: 310
    keef66 wrote:
    "I would imagine it will need moving down on the tube yeh?"

    Yes, so the front mech cage clears the teeth on the large chainring by 1-2mm

    cheers - Running Ultegra 6500 BB so I think that will likely need replacing? cheap 9 speed double compact here > http://www.ebay.co.uk/itm/Shimano-Sora- ... 46128a0e03

    Will this all work OK?
  • keef66
    keef66 Posts: 13,123
    6500 BB is Octalink, so yes, you'd need to replace it with any Hollowtech II BB to work with that chainset.

    eg http://www.chainreactioncycles.com/shim ... -prod67221

    68mm / English thread usually (depends on your frame / BB shell)
  • keef66
    keef66 Posts: 13,123
    Or you could just slap this chainset on your existing BB if it's still smooth

    http://www.chainreactioncycles.com/shim ... prod109701

    Might save on buying the HT II BB tools
  • greg66_tri_v2.0
    greg66_tri_v2.0 Posts: 7,172
    Have a look at a 52/36 set up - so called semi compact.
    Swim. Bike. Run. Yeah. That's what I used to do.

    Bike 1
    Bike 2-A
  • dubbs2009
    dubbs2009 Posts: 310
    keef66 wrote:
    Or you could just slap this chainset on your existing BB if it's still smooth

    http://www.chainreactioncycles.com/shim ... prod109701

    Might save on buying the HT II BB tools

    Keef66 - you leg end! I had not seen that chainset... that is what I'm after... then can keep BB as it's very good still... can then switch back later to standard if I wanted with just a movement of the front mech... awesome!

    this chainset says its 8 speed though? I am running 9 speed... this an issue?

    What tools will I need to remove existing chainset and install new one?
  • keef66
    keef66 Posts: 13,123
    Hmm, not sure about 8 speed chainrings / 9 speed chain. Anyone with any practical experience?

    As far as I know the Shimano Octalink stuff used self-extracting bolts; when you undo the thing first it loosens the bolt, then as you unscrew it further it becomes harder as it starts to pull the crank off. So all you'd need is the right size hex bit / allen key with an extension bar.
  • keef66
    keef66 Posts: 13,123
    Sheldon thought it would be OK:-

    "Chain. As you go to more sprockets on the cassette, you need a narrower chain. However, using a chain one size narrower than standard rarely presents any problem. Thus, you can use a "9-speed" chain with a 7-speed or 8-speed system, or a "10-speed" chain with a 9-speed system. This is not the ideal approach -- shifting may not be quite as smooth -- but it's workable.
  • dubbs2009
    dubbs2009 Posts: 310
    OK thanks Keef66 - sounds like it should work then. I will first stick a 27T cassette on and see how that works when climbing on the 39T inner big ring... then if that is still not suitable - I will look to get this new compact chainset and see how she works... Cheers for your help here
  • tomallen
    tomallen Posts: 34
    thecycleclinic wrote:
    If you are strong enough of a 53T you can handle a 39T inner.

    Sorry but this is nonsense.
  • meanredspider
    meanredspider Posts: 12,337
    tomallen wrote:
    thecycleclinic wrote:
    If you are strong enough of a 53T you can handle a 39T inner.

    Sorry but this is nonsense.

    I'm glad you said it because I was thinking something similar.

    I run a standard double on my bike that I use in NL. I also run a close ratio 12/23 at the rear. It's flat.

    On my Highland bike I run a compact and 11/28. It's not flat.
    ROAD < Scott Foil HMX Di2, Volagi Liscio Di2, Jamis Renegade Elite Di2, Cube Reaction Race > ROUGH
  • andy_wrx
    andy_wrx Posts: 3,396
    dubbs2009 wrote:
    What tools will I need to remove existing chainset and install new one?
    keef66 wrote:
    As far as I know the Shimano Octalink stuff used self-extracting bolts; when you undo the thing first it loosens the bolt, then as you unscrew it further it becomes harder as it starts to pull the crank off. So all you'd need is the right size hex bit / allen key with an extension bar.

    No, you'll need a crank puller
    topeak-universal-crank-puller.jpg

    Having removed the bolt from your 6500 crankset, you'll need to screw the puller in to get the cranks off the BB
    Notice that the one above has a blank/plug - as the Octalink BB has a hollow axle you'll need this in it for the puller to push against.
    If your puller doesn't have one, you can buy the Shimano-official one
    eg http://www.chainreactioncycles.com/shim ... lsrc=aw.ds

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