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  1. #1
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    Brompton Bottom Bracket/ Crank Upgrade

    Hi....anyone upgrade their Brommie bottom bracket and crank with lighter and more refined components?

  2. #2
    Bromptonaut 14R's Avatar
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    My BB was fine, but I did get an FSA crankset with 53 chainring for my Brompton.

  3. #3
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    More refined is easy, lighter is more difficult than you might think.

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    Hi
    I donít know if Mercís and Bromptonís respective parts weigh the same, but with Merc itís quite easy to save about 100g even without going for titanium or carbon parts. Mercís bottom bracket + left crank + right crank with 53 chain ring + chain guard = 1010g. Pedals were removed. I made a comparison with FSA bb + crank-set with 2 chain rings (50 and 34) and the weight saving was about 130g.

  5. #5
    Bicycling Gnome
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    Quote Originally Posted by maranen
    Hi
    I donít know if Mercís and Bromptonís respective parts weigh the same, but with Merc itís quite easy to save about 100g even without going for titanium or carbon parts. Mercís bottom bracket + left crank + right crank with 53 chain ring + chain guard = 1010g. Pedals were removed. I made a comparison with FSA bb + crank-set with 2 chain rings (50 and 34) and the weight saving was about 130g.
    To be honest, I probably carry 130 grammes of lose change in my pocket. I'd rather just leave that at home and not spend money buying new parts.


  6. #6
    Part-time epistemologist invisiblehand's Avatar
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    Quote Originally Posted by maranen
    Hi
    I donít know if Mercís and Bromptonís respective parts weigh the same, but with Merc itís quite easy to save about 100g even without going for titanium or carbon parts. Mercís bottom bracket + left crank + right crank with 53 chain ring + chain guard = 1010g. Pedals were removed. I made a comparison with FSA bb + crank-set with 2 chain rings (50 and 34) and the weight saving was about 130g.
    Would you use both chainrings or dump the 34?

  7. #7
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    Quote Originally Posted by invisiblehand
    Would you use both chainrings or dump the 34?
    I intended to use them both, but I will probably have to go for some other components because the axle length is not enough Ė bike will not fold Ė matter of 2mm. Otherwise itís very nice set FSA Gossamer Megaexo Compact with 50 chain ring same as K-Force Ė grooves and pins for better gear change. I had a chance to buy it quite cheaply and made a foolish thing not to check the folding first. The axle is integrated with the right crank. Actually weight saving would be 140g.

  8. #8
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    Brompton's cranks are lighter than the Merc's. The chainline and folding problems eliminate most of the lightweight options. Sticking to a square drive BB gives more freedom in that regard. As well as the chainring/spider clearing the frame when folded, another trap for the unwary player is ensuring the end of the cranks clear the folded swingarm. If you have this problem, you have to have the crank in a certain position before folding, which can be a real pain in the neck (refer Birdy and others).

  9. #9
    SeŮor Mambo
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    Quote Originally Posted by LWaB
    ...another trap for the unwary player is ensuring the end of the cranks clear the folded swingarm.
    I can confirm 165mm cranks work without having to position the cranks before folding. It also helps if your pedals fold, or can be removed outright.

    Also, 60T chainrings seem to be about the max size before the teeth and chain start rubbing against the chainstays.

  10. #10
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    What happens with a 170mm long crank?

  11. #11
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    Quote Originally Posted by delwong
    What happens with a 170mm long crank?
    Stock Brompton cranks are 170 mm. The problem is getting the same lateral offset from the chainring to the back of the crank at the pedal. Greater offset results in a wider fold, lesser can hit the folded swingarm.

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