Bottom Bracket Length question
 

I'm a newbie to the forum and want to get an opinion about a slight bottom bracket length mismatch.
My learning project bike is an '01 Diamondback MTB (curbside find treasure). The bottom bracket was dry and noisy so I pulled it. Its a square taper measuring 16.4 mm. The choices for replacement were 15.5 and 17.5 mm. I opted for the 17.5 which actually measures 17.8 mm. The entire 1.4 mm difference is on the drive side.
My question is whether that 1.4 mm is likely to give problems adjusting the FD and with shifting?
Thanks in advance and for the other great information presented here in the mechanics forum.

Well, the good news is that everything will clear. My preference is to run as short of a bottom bracket as I can get away with -- this minimizes the "Q factor" and allows the big ring to work with more of the cassette/freewheel. Most of the bikes that came my way had room to come in a little.

if you were only speaking of 1.4mm change on the drive side that would be fine.

But reading your post I suspect you have the wrong units and your measurements are actually in cm. If that's right, 1.4cm or 14mm is way too much difference, and you need to find a better match.

Oops. Guess I haven't successfully migrated to the metric system. A 17.5 mm BB would be a short one indeed.
Probably better go back and get the 15.5 CM BB. Thanks FBinNY and ThermionicScott for the helpful responses.

EDIT: Man, I need to get my head right. Dimensions were actually 116.4 and 117.8 mm, so 1.4 mm difference looks OK.

Aha, that sounds much better! :thumb:

Man, it's a good thing you're not cutting down a fork.

Yeah, that operation is a little more critical. ;)

The measurements in the OP confused me, but I figured he was measuring the length of the axle outside of the cups or something like that, where 1.4mm would indeed be a small change.

I love to pick on folks who make these UOM errors, but in all fairness the good folks at NASA crashed a lander into Mars the same way.