Conversion Kit BB specs
- Thread starter Vargas
- Start date
Anonsequitur
Member
Sofrider BB upgrade: Shimano BB-UN26, 68x123mm
Charles Plager describes on his blog that he has performed a crankset and bottom bracket(BB) upgrade using the following parts":
"For those fellow Sofriders out there, I used Alivio M411 Hybrid Crankset (Black 170mm X 48/38/28) with BB-UN26 cartridge BB, JIS - 68x123mm bottom bracket. "
http://recumbentquant.blogspot.ca/2012/03/new-crankset-installed.html
Charles Plager describes on his blog that he has performed a crankset and bottom bracket(BB) upgrade using the following parts":
"For those fellow Sofriders out there, I used Alivio M411 Hybrid Crankset (Black 170mm X 48/38/28) with BB-UN26 cartridge BB, JIS - 68x123mm bottom bracket. "
http://recumbentquant.blogspot.ca/2012/03/new-crankset-installed.html
Doug Burton
Zen MBB Master
Bottom bracket requirements
Bottom brackets are designated by their body width, axle width, and taper type in the case of square taper bottom brackets.
68 x 115 JIS taper = 68mm wide bearing body (which the conversion kit uses) x 115mm axle width, Japanese Industrial Standard taper, which defines the angle and dimensions of the taper for the square ends of the bottom bracket. Campagnolo uses the ISO standard taper, which fits poorly with crank arms other than Campagnolo or French cranks.
The axle width, in combination with the drive side crank arm type, determines the chainline dimension, which in turn determines how the chainrings align with the cassette. Axle width will differ depending on how many chainrings your crankset uses; the objective is to center the chainrings in the cassette width to make sure the chain is minimally deflected in any given cassette gear. Generally we are looking for a 47 - 50mm chainline dimension for conversions. Chainline is measured from the center of the adjustable front tube to the center of the center ring's teeth on a triple, and to the midpoint between the rings on a double chainring crank.
Additionally, road cranks tend to sit farther down on the BB axle taper than MTB cranks. So a bike using a road crankset may use a wider BB axle width to obtain proper chainline than an MTB crank on the same frame.
Charles is using a "trekking" crank (typically defined by the 48/38/28 chainring tooth counts), and these can follow either the road or MTB convention, with most in the MTB camp. If the crank you buy has a recommended BB, purchase that also or identify its specifications so you can match the BB to the crankset.
Folks tend to think of bikes as simple machines. My experience is the simpler the machine, the more subtle important things tend to be.
Cheers,
Doug
Bottom brackets are designated by their body width, axle width, and taper type in the case of square taper bottom brackets.
68 x 115 JIS taper = 68mm wide bearing body (which the conversion kit uses) x 115mm axle width, Japanese Industrial Standard taper, which defines the angle and dimensions of the taper for the square ends of the bottom bracket. Campagnolo uses the ISO standard taper, which fits poorly with crank arms other than Campagnolo or French cranks.
The axle width, in combination with the drive side crank arm type, determines the chainline dimension, which in turn determines how the chainrings align with the cassette. Axle width will differ depending on how many chainrings your crankset uses; the objective is to center the chainrings in the cassette width to make sure the chain is minimally deflected in any given cassette gear. Generally we are looking for a 47 - 50mm chainline dimension for conversions. Chainline is measured from the center of the adjustable front tube to the center of the center ring's teeth on a triple, and to the midpoint between the rings on a double chainring crank.
Additionally, road cranks tend to sit farther down on the BB axle taper than MTB cranks. So a bike using a road crankset may use a wider BB axle width to obtain proper chainline than an MTB crank on the same frame.
Charles is using a "trekking" crank (typically defined by the 48/38/28 chainring tooth counts), and these can follow either the road or MTB convention, with most in the MTB camp. If the crank you buy has a recommended BB, purchase that also or identify its specifications so you can match the BB to the crankset.
Folks tend to think of bikes as simple machines. My experience is the simpler the machine, the more subtle important things tend to be.
Cheers,
Doug
Charles.Plager
Recumbent Quant
Hi,
On the Sofrider, I
Hi,
On the Sofrider, I needed a 123mm bottom bracket for the M411. The 113 was too short and there wasn't enough space between the granny gear and the frame. I'm willing to bet the same is true for the M431.
Cheers,
Charles
On the Sofrider, I
Hi,
On the Sofrider, I needed a 123mm bottom bracket for the M411. The 113 was too short and there wasn't enough space between the granny gear and the frame. I'm willing to bet the same is true for the M431.
Cheers,
Charles
Charles.Plager
Recumbent Quant
Hi,
For what it's worth, I
Hi,
For what it's worth, I went with 170 since it was closer to the original 165mm cranks. I really didn't notice much (if any) difference between 165 and 170 mm cranks, I'm very happy with my 170mm cranks, but I couldn't tell you not to try 175mm cranks either (others with more experience may be able to do just that).
Doug's right: If you can figure out by visiting the Shimano website which bottom bracket goes with which crankset, that's the best thing to do. I don't know that the M431 is any different than the M411 and if they aren't, then you should be golden with the 123mm bottom bracket.
Let us know how it turns out.
Cheers,
Charles
For what it's worth, I
Hi,
For what it's worth, I went with 170 since it was closer to the original 165mm cranks. I really didn't notice much (if any) difference between 165 and 170 mm cranks, I'm very happy with my 170mm cranks, but I couldn't tell you not to try 175mm cranks either (others with more experience may be able to do just that).
Doug's right: If you can figure out by visiting the Shimano website which bottom bracket goes with which crankset, that's the best thing to do. I don't know that the M431 is any different than the M411 and if they aren't, then you should be golden with the 123mm bottom bracket.
Let us know how it turns out.
Cheers,
Charles
