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  • Shimano UN300 Bottom Bracket




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Genuine Brompton Bottom Brackets are great but just don't have the seals of a Shimano unit. The Fantastic Shimano UN300 is what our mechanics would replace a Brompton Bottom Bracket with here at Curbside.

Used and installed by 80% of the world's bike shops, this is a tried-and-tested unit that will have you pedalling smoothly for years to come. This model has a 68mm shell and a 118mm Axle which is a direct swap out for the Brompton unit.  

This bottom bracket is only compatible with the Brompton Spider Crank. The previous generation Stronglight crank with the integrated chainring used an ISO bottom bracket which is no longer available. If you have a previous generation crank and need a new BB, then you will also need to upgrade to a Spider crank.

  • Shimano UN300 Bottom Bracket
  • JIS Taper suitable for Brompton spider cranks
  • Durable, hard-wearing sealed cartridge bottom bracket with square tapered spindle fitting
  • Lightweight hollow spindle
  • Maintenance-free sealed cartridge bearing assembly keeps out dirt, mud, and water for long bearing life
  • Installed using a standard 22 tooth Shimano Bottom Bracket Tool
A BIT ABOUT BROMPTON: If you were to walk into the store and look at a Brompton we would say there are three things you should look for in a folding bike. All of them are fairly obvious. One, the bike should ride well - and, on a small wheeled bike that's tricky because there's a fine line between maneuverability (which is a virtue) and twitchiness (which is a vice). Two, the bike should fold well - otherwise you're blood pressure will rise and you'll curse the day you bought it. Third, it should be transportable, or highly storable - because that's the whole point, right?

Brompton is the only company we've seen that answers all three criteria - and believe us, we've tried every brand out there. The reason others can't compete is because Brompton has answered a fundamental engineering problem. If a bike is going to unfold to a large footprint (which takes the twitch out) then it is unfolding to a bigger bike - and by all logic, a bigger bike unfolded would be a bigger bike folded. So, it's pretty much true that for most folding bikes they either have great rideability but poor transportability or vice versa. And nearly all of them are a mess to fold.

Not Brompton. Brompton has designed the Platonic form of all folding bikes. The bike folds to the smallest size on the market, unfolds in a highly precise and easy manner, and has the same axle-to-axle footprint as a hybrid bike. How did they do this? By not only designing a clever frame, but also designing some 1200 proprietary parts that make everything fit - and fit perfectly. Oh, and nearly all of this is made in England. No wonder this bike has a cult following.


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