Originally Posted by
joefelixj
Hi guys,
I recently bought the low end Specialized Sirrus 2018 for use riding around the city. I'm super happy with it so far however I want to make some modifications.
I've realised I only ever use the big chainring (48t) as the city is fairly flat - and my cassette goes up to 32t which seems to be a more than low enough gearing for my needs.
Given this I thought I would convert the bike to a 1x with a single 48t chainring at the front. (I also think it will be fun to have a little project, and learn a bit more about bicycles).
I was originally going to start by just removing 2 of the chainrings from the crankset. However I realised they were welded together. Then I was going to just replace the chainrings with a single one from a company like Stronglight, but then I realised they were welded to the crankshaft! I'm not surprised as all the components are Shimano Tourney which is bottom of the range.
So now I've arrived at the decision to replaced the whole crankset. This should also give me a bit of a lighter bike - and hopefully be more rigid for power transfer too.
I've had my eye on the Stronglight Mygal Messenger and the Stronglight Track 2000. They both have 48t configurations available, are not too expensive, and people seem to trust them.
On their website they say "Reccomended bottom bracket: JP 400 with aluminium cups 103 mm lg. (conical square JIS)".
Now my bottom bracket is described as "BSA, 68mm, square taper".
I believe that 68mm and 103mm are describing different things. I think 68mm is referring to the width of the if the bb - whereas 103mm is referring to the length. However I'm not sure.
So my question (finally) is - do you think that these cranksets will fit on my bb?
And if not - do you think a Stronglight bb e.g. JP 400 AL will fit in my frame? (it says " 68 mm and 70 mm frame boxes (BSC/ITAL)" but mine is supposedly BSA...)
links to everything I mentioned:
I wanted to link to all the products I mentioned but as it's my first post I can't.
However the product ids on the stronglight website are: 397, 222 and 210
And my bike can be found on the specialized website with the url-ending "/us/en/mens-sirrus-alloy---v-brake/p/129091"
Thanks everyone!!!
Im actually trying to do the same exact thing with a 2015 Specialized Sirrus and you are correct that when they recommend a bottom bracket they are likely referring to the spindle/axle length (103mm #) while specialized is referring to the width (68mm #). The Square taper BB currently on there has a spindle thats probably / will be too long as its designed to handle a 3 ring chain ring. If you just mounted that crank set on that bb the chainline would be too wide so i was planning on replacing the BB as well when i convert mine, just having some trouble figuring out which spindle length to go with (Shimano UN55 looks to be a good square taper bb). im not an expert and someone will probably have more insight but thought id give my 2 cents
are you planning on leaving the front derailleur on there? I want to take mine off so ive been making sure any chainrings i look at are narrow wide ones so the chain doesnt fall off but not sure if that is overkill for a commuter