New BB.crank setup

The Rookie
The Rookie Posts: 27,812
edited May 2010 in MTB workshop & tech
My Daughters Scott (no idea of model, its been resprayed!) has knocked out its BB, its Truvative ISIS, but her axle is 123mm and the cheapest I can find is £70 which its just not worth having (118mm would have been OK)

So we are figuring on getting a whole new front end setup, however the bike has very fat chain stays, even with the 123mm axle the cranks run within 2mm (probably less) of them, so if I'm looking to get a whole new setup, what 'measurement' do I need to look at to make sure the cranks don't hit the chain stays? Is there a 'theroretical' gap across between the crank arms (assuming one crank fitted 180 degrees out as such) that I can ask for? We are looking at the Deore Hollowtech on CRC for £50.

http://www.chainreactioncycles.com/Mode ... elID=40496

Tech specs http://techdocs.shimano.com/media/techd ... 677251.PDF

I do still have to check the chainline as 50mm, but I can't see a measuremnt to help with my concern!

Simon
Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.

Comments

  • nicklouse
    nicklouse Posts: 50,673
    what are/were the cranks_

    truvativ what?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
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  • The Rookie
    The Rookie Posts: 27,812
    Sorry,
    Front says Truvative ISIS Firex, markings on the rear are FX3CAF.

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • supersonic
    supersonic Posts: 82,708
    WIth the Firex on, what is the measurement for your front chainline?
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  • The Rookie
    The Rookie Posts: 27,812
    Front Chainlne is 54mm to the 'middle' ring (as its running 2+bash its actually the new outer).

    For info if you create a virtual ring where the rear of the crank arm circles they need to be at leat 14cm apart to clear the chain stays.

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • supersonic
    supersonic Posts: 82,708
    That is known as the Q factor.
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  • The Rookie
    The Rookie Posts: 27,812
    Brilliant, thanks SS, so obviously it can only be quoted for a whole assembly? Shimano don't mention it in their tech docs.

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • supersonic
    supersonic Posts: 82,708
    It is usually a roadie thing as it effects efficiency.

    Seems like you have an oddball frame.
    GT ZASKAR CARBON TEAM

    VOODOO CANZO

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  • The Rookie
    The Rookie Posts: 27,812
    OK, but when looking at a setup, how do I know if it will fit? The Shimano docs for example (as linked to above) don't list it!

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • supersonic
    supersonic Posts: 82,708
    Not easy to. Very often keeping to the same chainline is close enough.

    Narrow Q factor cranks. are usually stated.

    My advice is to get a square taper crank and BB that is 8mm longer than usual.
    GT ZASKAR CARBON TEAM

    VOODOO CANZO

    Come and see me at https://www.facebook.com/biketyke/
  • The Rookie
    The Rookie Posts: 27,812
    OK thanks SS, that won't please the Daughter, she's trying to keep it 'classy' and wants something better than square! In fact she's just got an XT rear mech to replace the Deore on there!

    I guess the other option is to talk to my local MTB breaker and see if he has a combo that will fit and be suitably up market, the daughter better get that Job (Halfords BikeHut) she has the interview for tomorrow!

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.

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