biknbrian

I need to replace the BB on one of my bikes. The installed BB is Shimano square taper 110mm. However the place from which I'd like to order (due to needing many other things) is temporarily out of stock of this size. Also I've noticed that my left crank arm is slighlty father from the frame than the right arm. I'd like to correct this if possible.

What effect would using a different BB width have on crank arm positon? Would a shorter (108mm) BB move the left crank arm in slighlty as I seem to think for some reason?

Ex Pres 

110mm Shimano BB = 107mm Shimano + (oddly enough) 3mm on the non-drive side, so buy a 107mm

biknbrian

Thanks, but I'm still trying to understand the issue. Where can I find this information?

I've looked at Sheldon Browns site, but it claims my Doere crank requires 110mm to 113mm. I seem to recall that old cone and cup spindles usually moved the left crank out as size increased which is whay I thought cartridges were the same.

What I'd reall like to be able determine is how far the left and right spindle ends move from size to size. A nice reference point would be from the right face since it is essentially fixed once it bottoms out. Then I'd be able to determine that the if right end spindle protruded some length for nice chainline what size overall cartrigde I'd need to put the left spindle end exactly the same distance out.

San Rensho 

The BB size determines how far out your right crank is, and thus it defines your chainline. I believe that the distance of the left hand crank from the frame is the same for different size BBs.

So if you want to maintian your current chainline, get one that is the same size as the one currently on the bike.

However, measure your current chainline, if its off a little, you may be able to use another size and actually get a better chainline.

Nashbar has a 110 BB in stock.

biknbrian

So you're saying that a longer BB moves the right arm out, but the left arms stays the same? Bob says that a 107 shimano moves the left arm in versus a 110 shimano while the right stays the same. If Bob is right then my current problem is solved, but these two pieces of information conflict.

I've replaced a few BBs size for size, but I've been having problems dealing with making a size change. Also I've got a frame I'm going to be building up, and I do not know exactly what size BB I need. It is claimed that if I have a new crankset then I should be able to just look up the size I need, but this is not true. Plus I'm using an old crankset anyway.

The width of the this old Fuji frame at the bottom bracket is different from my Iron Horse Commuter MTB which also uses a square taper, not a lot but enough to effect arm position. A wider frame is going to shift the right spindle outward and the left inward, narrow means the opposite.

I can easily slap in an old known size BB, mount the diesired crankset, and determine that I need to move the right crank ???mm and the left crank ???mm. The problem I'm having is figureing out how to use this info to determine the cartridge I need. I do realize the a compromise may be necessary, but with the right info I could pick the best available size.

Do I really have to run amok at the LBS with a micrometer cataloging right face to spindle end measurements? I'll do it if I have to.

Ex Pres 

In many cases you are correct that a wider spindle moves the right (drive) arm out further as the spindle gets longer, while the left stays fixed. The 107mm vs. 110mm Shimano BB is very much an oddball.

As far as a chart that shows symmetric vs any asymmetry on all model numbers - please post one when you find it.

operator

Just slap on some bb in the neighbourhood of the right answer and eyeball the chainline.

Bill Kapaun

Is the current BB a cartridge type, or adjustable cup/spindle type.
If the latter, many were built with an offset.
My 86 Rock hopper & 91 Trek 820 both have a spindle with a 3MM additional "length" on the drive side. (3P)
Sheldon has a chart for "equivalent" symmetrical cartridge types.
About 1/2 way down the page, look under"
Old-style Cup-and-Cone Bottom Bracket Parts"


https://sheldonbrown.com/harris/bottombrackets.html

biknbrian

Thanks, that's basically what I was asking for. Your info on the 107mm will solve my current problem and allow me to order from JensonUsa.com which is the only place that has all the things I want right now. In the future I may just have to go to the LBS with an old BB or some measurements and ask for one that's a bit longer here, or shorter there, or whatever I need.

biknbrian

I happened to have a "Nahsbar" 113 mm BB that I was going to use for something else.

If anybody cares, it is made by Tien Hsin is actually only 1 mm longer than my 110mm Shimano UN40. It adds 2mm to the right spindle, but shortens the left by 1mm versus the UN40. It still kills me that you can find out all about darn near every rim and hub every made in order calculate spoke lenghts, but no one seems to have BB measurements.

I'm going to start compiling a list of measurements of the ones I come across. If anyone wants to they can send me measurements if they know or can measure them. Of course I'd need make and model plus claimed length, actual length, and measurements from the right face where the cartridge would contact the frame to each spindle end.

Ex Pres 

One of the C&V guys has some info that will add to your quest. I don't remember who, but post a thread there with an enticing title