Spindle length
 

What's wrong with this picture?


https://cimg2.ibsrv.net/gimg/bikefor...0c40e7ca17.jpg

I have a 2x9 on my Sirrus. Crankset is FSA Vero. It was getting noisy so thought about replacing BB with UN55. From my research, the current BB was RPM, 110.5mm. I also read that 110 was common for 2 ring, and 113 common for 3 ring. That is why I bought the 110mm version of the UB55. When I removed the BB it was marked 113. Measurements indicated it was in fact 113mm.

Why is the UN55 measuring 112mm? What would the 113 mm version UN55 measure? Are these numbers more arbitrary than we make them to be?

Manufacturing tolerance and/or miss labeling. But I'll add that a chainline changing by about 1.5mm shouldn't be any big deal. Unless you're already at the limit of chainstay clearances and that 1.5mm is in the wrong direction. Andy

It is not unusual to see a spindle on Shimano bottom brackets not be there length printed on the cartridge... But it doesn't seem to effect anything.

This may be a photo problem.

The spindle does not appear to be symmetrical. The left side appears to be longer than the right because there is no round section showing on the right side. This used to be normal - the driving side was longer than the non-driving side. In this case, it appears that the non-driving side is longer.

That is the way it is made. Also, the angle of the shot makes it more apparent.

If you think about it, it doesn't really matter where the end of the spindle is- (imagine the taper continuing to a point....)
It's the length where that "magic dimension square" is that stops the crank arm from further travel when properly torqued.

Not much to those who follow these things. Shimano's bottom brackets don't always measure exactly per the nominal length. My hunch is that it's to make sure everything clears: Shimano UN54 Cartridge Bottom Brackets Relative Chainline ? Harris Cyclery Blog

There's more to it than the crank position relative to the taper. There's the question of whether the crank or chainwheel will clear the chainstay. Although, there's the question whether the crank and spindle tapers match (ISO vs. JIS). That's a couple of mm clearance in either direction.

https://cimg1.ibsrv.net/gimg/bikefor...da3fa29285.jpg

Here's are Campy's bottom bracket clearances. A 110 mm length spindle is for a single speed. Campy typically had the shortest spindles and tightest clearance between chainstay and crank/chainwheel.

https://cimg4.ibsrv.net/gimg/bikefor...307620a6df.jpg

Here's a typical chainline diagram.
If the driving side is too close to the bottom bracket, then the crank or chainwheel won't magically clear the chainstay, as it does in this diagram. N.B. the chainstay is crimped to give smaller chainwheels clearance for doubles and triples.

That's why I'm puzzled why the non-driving side is longer than the driving side. Look at the dimensions, when non-symmetrical spindles were the order of the day. The driving side was longer to insure the clearance. Putting the spindle in backwards and not having chainwheel clearance was a rookie mistake.

Until I see a better photo (without the drive side taper partially hidden) I won't say this spindle (actually axle as it is the rotating element) has off set tapers. The drive side "cup" flange hides the base of that side's taper from view.

As I mentioned in my first post there's some manufacturing tolerance WRT the ends of the taper. As always the best way to find the best BB axle length/fit is after test installing. Andy

Left and right side are symmetric.

RPM spindle length was dead on at 113, which it was marked as. 2mm error on 110mm spindle for a machined part is very poor precision. If a UN55 113mm version has that imprecison, then what is the point of having both 110 and 113 mm models, as one 110mm sample may be equal to a 113mm sample? Or are all UN55 110mm models 112mm?