BB Help

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  • Hello,

    I have a question if anyone can help,

    I have an old Sugino Messenger spider that i would like to potentially put on a 90s MTB build?
    However as you know the chain stay on a 90s MTB is wider than a road bike etc.

    I don't know if this is a stupid question but would it work if i used the longest axle that shimano UN55 make?

    Current BB Shell length: 73mm

    Thank you for your help.

  • Just checking the obvious... The Sugino Messenger is a single speed crank and can only handle one chainring. You're intending to build a bike with a single front chain ring, right?

    If so, using the Sugino Messenger with a 103mm BB will give you a 45 mm chainline (apparently, according to some Googling).

    Sheldon Brown's article on chainline says that triple MTB chainline should ideally be 47.5 mm (i.e. the middle chainring is 47.5 mm outboard from the centre of the seat tube). So to achieve that you'll need to add 2.5 mm on each side, meaning +5 mm to the BB length... 103 + 5 = 108 mm BB

    So don't choose the longest BB because I think, for Shimano UNxx, that's actually 122 mm ish. Way too long.

    Just another note... That crank was originally intended for 1/8" thickness chainrings but you'll need to put a 3/32" ring on there for use with gears. Just in case you were about to buy another Sugino ring.

    Of course, if you want more than one chainring up front then best procedure is to sell this crankset and buy a double/triple chainset/crankset.

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BB Help

Posted by Avatar for Throughbeingcool @Throughbeingcool