Bicycle Mechanics - Bottom Bracket Length
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I ride a Redline Mono 9 and the original spec says the bottom bracket is 68mm x 108mm. Will a 68mm x 113mm make that much difference in chainline? 113mm seems to be the most common ISIS length.
07-29-09, 08:50 PM
Yes it will make a difference but one of the catches is that the chainline often isn't what the specs say it is so a different axle length is called for. Now the problem is that the most common error is that the chainline is WIDER than spec so the last thing you need to do is to deliberately make it wider still.
Measure it to see where your at. Measure from the centre of the seat tube or down tube to the chainring. I'm assuming it has a single ring on front? If its a double you measure to halfway between the two rings and if its a triple you measure to the middle ring.
07-30-09, 09:09 AM
Are you changing cranks? The crankset is the most significant single factor in determining the proper BB spindle length.
07-30-09, 09:20 AM
I've figured out why manufacturers use that stupid 43.5mm to a point in between the chainrings, that can't be measured. It's far easier to check to the tip of a tooth on the little ring when the FD is in place. That should be very close to 40mm. The big ring would be in the 47-48mm range. Measure from the side of the seat tube and add half the diameter.
I'm not changing cranksets and yes it just has a single ring in the front. I think I can figure it out from here. Thanks for the help.
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