Bicycle Mechanics - BB length

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dedhed
02-14-10, 12:23 AM
I need to replace the sq taper cartridge BB (9spd Deore triple crank) on my Raleigh C500 hybrid rain commuter.
The original cheesy Chinhaur is 68mm X 111mm English. I plan on replacing it with a Shimano UN54.
The shimano comes in 110 and 113mm lengths. Would the recommendation be to go 1mm shorter or 2mm longer? The granny ring is almost never used. It "appears" that either will not interfere with the frame etc. I'm also assuming I'd need to adjust the FD (lx) stops after too.

AEO
02-14-10, 12:29 AM
for a triple and a frame that can fit wide tires? 113mm is the safe bet.
operator
02-14-10, 12:48 AM
I need to replace the sq taper cartridge BB (9spd Deore triple crank) on my Raleigh C500 hybrid rain commuter.
The original cheesy Chinhaur is 68mm X 111mm English. I plan on replacing it with a Shimano UN54.
The shimano comes in 110 and 113mm lengths. Would the recommendation be to go 1mm shorter or 2mm longer? The granny ring is almost never used. It "appears" that either will not interfere with the frame etc. I'm also assuming I'd need to adjust the FD (lx) stops after too.

Before we get anymore guesses you should tell us whether that 111mm is symmetrical or not. That will greatly affect the correct answer.

dedhed
02-14-10, 01:43 AM
Measurements of the spindle end to cup face with the NDS adjustable cup bottomed on the cartridge. DS (R) = 17+mm NDS (L) = 19mm

With adj cup removed spindle to bearing face NDS = 25+mm
Torchy McFlux
02-14-10, 03:34 AM
According to this:
http://bike.shimano.com/publish/content/global_cycle/en/us/index/tech_support/tech_tips.download.-Par50rparsys-0032-downloadFile.html/05%29%20Crankset%20and%20BB%20Combination%20Chart.pdf
Either a 110 or a 113 will be OK. (It is an FC-M510, right?) A 110 would give a better chainline, but a 113 might be a good idea if you have a 35.0mm diameter seattube and/or 73mm wide bottom bracket shell.
dedhed
02-14-10, 08:59 PM
Thanks for the chart. Yes, FC-M510 crank.
Here's what I did. Reassembled drive side. Measured ST @1.25". Measured from far side of seat tube to middle ring 2.56". minused .625" for ½ of ST dia for 1.94" chainline X 25.4 = 49.3mm chainline (as well as I could eyeball caliper to ring). According to the chart 50 mm chainline should use the 113mm length. I'd also lean toward the longer given the low use of the granny especially granny big combo. Does this make sense?