Help! BB advice

[Stressed]

Says 24 on the BB. Perhaps it is just badly made.

Could be! Just to clarify- when you say it's 'too short', does that mean the chain rings are hitting the chainstays?

 

[BarneyRubble]

I've got a nearly new 73mm, 122.5mm Shimano UN55 in the garage if you want it (£12 + postage). By 'nearly new' I mean that it was fitted and used for less than 100 miles, then removed.

Thanks. As it's the second one I've brought for the bike, I'll see if I can get a refund or replacement. I may be in touch!

 

[BarneyRubble]

Could be! Just to clarify- when you say it's 'too short', does that mean the chain rings are hitting the chainstays?

Yes

 

[Stressed]

Could be that it's JIS rather than ISO standard- taper/spindle end is narrower so the crank will be closer...

 

[BarneyRubble]

Could be that it's JIS rather than ISO standard- taper/spindle end is narrower so the crank will be closer...

I didn't know there were different tapers? Jesus what a pain. So my BB that fits the frame has a taper that's too small?

 

[BarneyRubble]

I didn't know there were different tapers? Jesus what a pain. So my BB that fits the frame has a taper that's too small?

The RPM one says JIS on the label...

 

[Stressed]

I think this'll explain the issue:
"ISO and JIS are very similar – the angle of the taper is the same, but the ISO spindle ends are a little slimmer. In a pinch, you sometimes can use a JIS spindle with an ISO crank. To compensate for the wider JIS taper, select a spindle that is about 1-2 mm shorter. The other way around doesn’t always work: A slim ISO taper can extend all the way through the larger hole of a JIS crank, so you cannot tighten the crank."

 

[BarneyRubble]

I think this'll explain the issue:
"ISO and JIS are very similar – the angle of the taper is the same, but the ISO spindle ends are a little slimmer. In a pinch, you sometimes can use a JIS spindle with an ISO crank. To compensate for the wider JIS taper, select a spindle that is about 1-2 mm shorter. The other way around doesn’t always work: A slim ISO taper can extend all the way through the larger hole of a JIS crank, so you cannot tighten the crank."

OK thanks. I think the RPM one would be wrong even if I could fit it. Almost certain that BETD will be making the RS7 cranks to ISO standard. I've never had a problem with them on a standard shimano BB in the past.

My god I just wish bike and component companies could agree on some actual "standards".

 

[Stressed]

All good though: CassidyAce'll sort you out

 

[BarneyRubble]

All good though: CassidyAce'll sort you out

Just checked and the cranks are JIS taper, so maybe the Shimano BB is ISO.