how to make a 30-46 cyclo cross chainset

karnali
karnali Posts: 703
edited December 2009 in Workshop
mu commuter andcx bike currently has a 34 50 chainset, i spend most of the time in 34 when commuting although some time in 50as well. I live int eh lakes so not many cross races buts lots of options for mixed training rides. The only race it gets used for is the 3 peaks. HAd 34 32 on for that and could have done with a lower gear.

I'm thinking a triple road chainset and remove the 39 and 50 and ut ona 46 t ring ( ithink i will need to buy and outer ring will this fit ok on the mile position.

a mtb set up and use either 29 on the inner or more likely 32 and buy a 46 outer and get a 34 cassette. Will this be award to get a good chainline. 68mm bb shell

or a middleburn duo set up of 29/30 and 44 ithere biggest outer , what lenght bb axel would i need on the isis or square taper

cheers

Comments

  • maddog 2
    maddog 2 Posts: 8,114
    both the mtb setup and the middleburn will have a large Q.

    The road triple will be better I suspect, but obviously not as narrow as a double/compact. And if you only run the inner two rings then it'll look a bit odd, if that matters.

    Some say a wide Q is no big deal but with the mtb/middleburn setup the chainline is poor and it's simply too widely spaced IMO for anyone who doesn't ride a horse regularly. I ran a Duo with a 107mm square taper for a while and it's well made but the Q is too big and the shifting is rubbish, in a word.

    If you want to run say, 32/46 with decent shifting and a roadie chainline then the only way to do it IME is to use a TA Carmina chainset with a 4-bolt spider, on a 107mm square taper BB.

    This way you can run 4-bolt MTB rings - so shifting is good, and you get a proper roadie Q and chainline. I run this setup on the wife's bike. Not cheap though.

    Having said that, a standard road compact will go down to 33t and paired with a 11-34 cassette will go pretty low (26.2 inches). And if you run 10speed you could also go with the new SRAM XX on 11-36...

    See dotbike for the TA Carmina stuff.
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • karnali
    karnali Posts: 703
    hi where can i get a 33 ring from ?
  • maddog 2
    maddog 2 Posts: 8,114
    http://www.dotbike.com/ProductsP2466.aspx
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • W_J
    W_J Posts: 1
    I'd agree that using a mountain bike chainset on a cross bike will make the Q-factor too wide given the width of typical cross stays (mtb cranks put the pedals about 20mm further apart). The 50mm chainline on mountain bike chainsets doesn't work well with a road front mech. Middleburn are bringing out road cranks soon by the way.

    I've used a road triple with 28-44 fitted on the inner two rings combined with a road front mech successfully. (double road mechs are designed for 43.5 mm chainline, a road triple has a 45mm chainline but if you only use the inner two rings it's 42.5mm) On my carbon frame I couldn't get the front mech quite low enough for perfect shifting as the rear chainstay clashes with the mech cage. This should be ok on a steel or aluminium frame though.

    I used the above with a sram 11-28 10sp block in the 3 peaks and got good use of the 28-28 bottom. If you've got a 9speed rear it's easier just to put a 11-34 block on and a mountain bike rear mech.

    http://www.sheldonbrown.com/chainline.html has info on chainline. Wiggle and sjs cycles have a good range of rings.

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