Betsy
Old School Grand Master
Excuse the thread jacking.. I've got similar Q's a bit of summing-up, some musings and occasional ramblings.. so why not keep it all in one place
I'm removing a Middleburn crank with 2x chainrings from my RC200 and replacing it with a CBR RSR with 3x chainrings.
The existing BB is Shimano JIS x 113mm spindle.
All tapers are nr perfect, the Middleburn crank arm when pushed (by hand) onto the JIS taper sits like this
The CBR sits like this
Re- Middleburn.. the distance from the thread recess to the end of the spindle is 2.2mm (we'll call this distance A) it was probably closer to 1mm before i pulled the crank.
Same distance on the CBR (we'll call this distance B) is 4.5mm so it does seem that @M-Power is right and the RSR should be mounted on ISO or preferably their own BB
There are so many conflicting viewpoints around the interwebs!!.. even checking this thread it looks like the CBR crank sits a lot further down the JIS taper than mine does... not sure if this is RSR version or not?
Now here's the fly in the ointment.. obv's i need a different BB and measuring the chainline a 127mm spindle length should work (a'la MP) but when the 113mm BB was in situ, i pushed the CBR crank onto the spindle until the smallest chainring hit the frame, 'distance B' measured 7mm so 7mm +7mm +113mm = 127mm so if i used a 127mm ISO BB the smallest chainring could be hitting the chainstay, if i used a 127mm JIS BB the spacing would move the chainline out but give the clearence needed to move the chainring away from the frame.. BikePro recommend 122.5 ??
With the smallest chainring hitting the frame i have a 49mm chainline at the front and 45mm at the back.. which looks about right.
Here in the UK i can buy a 127mm Shimano UN-300 for £20 from LBS but i'm struggling to find a 127mm ISO BB, i don't mind paying for a decent BB if i'm 100% confident that i've got the sizing right..
Folks are running CBR RSR on RC200's so what BB are they using??
Bonus crank shot
Opinions welcome?
I'm removing a Middleburn crank with 2x chainrings from my RC200 and replacing it with a CBR RSR with 3x chainrings.
The existing BB is Shimano JIS x 113mm spindle.
All tapers are nr perfect, the Middleburn crank arm when pushed (by hand) onto the JIS taper sits like this
The CBR sits like this
Re- Middleburn.. the distance from the thread recess to the end of the spindle is 2.2mm (we'll call this distance A) it was probably closer to 1mm before i pulled the crank.
Same distance on the CBR (we'll call this distance B) is 4.5mm so it does seem that @M-Power is right and the RSR should be mounted on ISO or preferably their own BB
There are so many conflicting viewpoints around the interwebs!!.. even checking this thread it looks like the CBR crank sits a lot further down the JIS taper than mine does... not sure if this is RSR version or not?
Now here's the fly in the ointment.. obv's i need a different BB and measuring the chainline a 127mm spindle length should work (a'la MP) but when the 113mm BB was in situ, i pushed the CBR crank onto the spindle until the smallest chainring hit the frame, 'distance B' measured 7mm so 7mm +7mm +113mm = 127mm so if i used a 127mm ISO BB the smallest chainring could be hitting the chainstay, if i used a 127mm JIS BB the spacing would move the chainline out but give the clearence needed to move the chainring away from the frame.. BikePro recommend 122.5 ??
With the smallest chainring hitting the frame i have a 49mm chainline at the front and 45mm at the back.. which looks about right.
Here in the UK i can buy a 127mm Shimano UN-300 for £20 from LBS but i'm struggling to find a 127mm ISO BB, i don't mind paying for a decent BB if i'm 100% confident that i've got the sizing right..
Folks are running CBR RSR on RC200's so what BB are they using??
Bonus crank shot
Opinions welcome?
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