Bicycle Mechanics - rear triangle and BB

Hi,
If I spread a rear triangle (according to SB) should I replace the BB with a longer spindle? In other words, if I open the rear triangle let's say 6mm, should I get a BB with a longer spindle equal to that length?

No. Rear wheel will still be centered between dropouts with 3mm of spacers on each side.

Actually, that's an interesting question.

The rear chainline is measure to the center cog of the sprocket cluster, which would be located 6mm/2 = 3mm farther from the center of the dropouts if the cluster is the same width as the old one. So it would seem that the front chainline should be moved out 3mm to match. Otherwise,

chainline difference = (spread/2 - (cluster width difference)/2)

I'd like to see that demonstrated by measurement, though, before I acted on it.

Yeah, assuming the reason you cold set the frame is to use a different, wider O.L.D. hub, you've probably changed your optimum chainline some. One of the main ideas behind bb spindle length is to get as close to optimum chainline as possible, so it seems likely you might need a slightly longer bb spindle for the best chainline.

No. Rear wheel will still be centered between dropouts with 3mm of spacers on each side.
Fixed Gear thinking.^^^^^^^:o


well biked is right if you are going from 130mm to 135mm. or some other spacing variation(geared)

thanks

All the pale bike rider needs is a suntan. :)

:
All the pale bike rider needs is a suntan. :):roflmao:

Hi,
If I spread a rear triangle (according to SB) should I replace the BB with a longer spindle? In other words, if I open the rear triangle let's say 6mm, should I get a BB with a longer spindle equal to that length?

It depends on the centerline of the rear cluster you are installing vs. the centerline of the chainwheel set. Need to properly spread the triangle so centered and then check chainline to see what is needed. See Sheldon for chainline info - redundant to go into it here.