Technical advice on compact crank

Discussion in 'Road Cycling' started by cyclintom, Dec 4, 2019.

  1. cyclintom

    cyclintom Well-Known Member

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    I presently have a Redline Conquest cross bike. It has an "oversize" shell width (73 mm). Presently it has BB-MT800 cups on it. I like the idea of a 24 mm crankset shaft but the Reynold's compact crank I tried to install was too narrow.

    I guess that the Ultegra has a shaft diameter of 24 mm but is it long enough to fit through here? I really can't remember if they had a spacer that you would install for a "normal" (68 mm width shell) so that you could use the cranks in either case.

    Can anyone give me some advice on this? Damned if I have been able to discover this sort of information anywhere and on other groups I end up getting a ration instead of knowledge.
     
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  2. BrianNystrom

    BrianNystrom Active Member

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    The 73mm BB shell was actually the standard for mountain bikes with threaded bottom brackets, back before the explosion of different BB types. There are many threaded BBs that come with a pair of 2.5mm spacers for use on 68mm BBs, and you just need to leave those out. I don't have a specific crank recommendation, but if you search the web for "bottom bracket compatibility chart", you'll find information on all the major brands. It will probably take some time to weed through it, but it will be worth the effort. If you go with a crank with external cups, either a 24mm or 30mm spindle will work, so don't limit yourself to 24mm. It's possible that you may end up with an MTB crank.

    BTW, contact Redline and ask them for crank recommendations. Look at other bike models in their line to see what they use.
     
  3. cyclintom

    cyclintom Well-Known Member

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    Thanks. I bought an almost new Trek Emonda and fit a normal Ultegra 8000 cranks. The off-size of the crank appears to strike the chainstay slightly and there isn't a spacer in the box. Now the crank can be mounted slightly outwards enough and still be further on the s;plines than on the Redline which has a 6800 crank, but it can move back and forth slightly on the bearing races and touch the stay. Is there supposed to be a spacer here that wasn't included in the new crank?
     
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