Hoping that the hive mind of Bromptoneers (is that a word?!) can help me here. I am about to embark on a significant upgrade to my S3L by fitting Shimano Dura Ace 170mm cranks, overkill I know, but I have them, so why not 🙂 The cranks came with a BB-MT800 and were previously fitted to a Brompton. The BB feels "OK" but if I am going to the effort of fitting it, I thought for £20 or so, I might as well fit a brand new BB as I have no idea how many miles are on this one (and one side feels "different" to the other).
Easy I thought, just Google "BB-MT800" and press "Buy"! Then I realised that there are more than one, and I want to make sure I get the right one!
I know the Brompton is a 68mm size, but which of these should I go for? One says its for the BMX type, but also comments that its with a "short sleeve". The pictures on the websites are all the same, I just want to make sure I get the right one….!
Any advice/help gratefully received 🙂 PFA below…
by WhichArtichoke1169
3 Comments
I think this post has answered my own question – just the standard BB-MT800 will be fine. I have the 7800 Dura-Ace cranks too…
[https://handsonbike.blogspot.com/2017/08/brompton-m6r-shimano-crankset-and.html](https://handsonbike.blogspot.com/2017/08/brompton-m6r-shimano-crankset-and.html)
be VERY VERY aware that the threads on older brompton BBs are not concentric and are quite crooked in most cases. If you are going to install external BB cranks then make sure you have the threads chased and the BB shell faced before installation or axle won’t fit or the bearings will wear out very quickly.
This reminds me of my journey of trying to find a fitting 160mm crankset.
I have very short legs and wanted to fix my kneepain while riding.
I don’t have anything useful to contribute except: mind the difference in Q factor of the pedals.
The original are asymatrical because the BB is offset.