Bottom bracket spindle lengths

[rrarider]

After many years, my bottom bracket became noisy and I replaced it. The model that was worn measured 127.5 mm, so that it is the length of the replacement that I fitted. The replacement is fine; only a slight amount of twiddling with the limit screws was necessary and the inner chain ring clears the chain stay by an adequate margin.

I think I will get a spare bb in case of future failure and I see that 127mm and the 127.5mm are common options - almost de facto standards. I can't imagine that a 127mm version on my bike, with a quarter of a millimetre length difference on each side, would make any performance difference, so I may well buy a 127mm version.

It prompts me to ask the question here : "why would 2 length options, so close together, be so commonly available?"

 

[Hugh Manatee]

127mm is exactly 5 inches, (I looked it up). I can only think parallel systems ending up being very close. Although why you would go for the extra 0.5 on the metric is anyone's guess. Perhaps on paper, 127.5 gives the perfect solution.
Like you say though, 0.25mm either side isn't going to make any difference at all.

This whole post is a guess/theory. Quite an old chainset is it?

 

[rrarider]

This whole post is a guess/theory. Quite an old chainset is it?

It's a Sugino GS chainset as supplied with a 1984 Raleigh lightweight.