[slyfink]

So the old school BSA ball retainer bottom bracket and cranks on my son's Commençal keep coming loose. I was looking to replace it with some proper cranks, but couldn't find any MTB cranks that are short enough (I'm looking for a 150mm or 155mm).

Then my research brought me to these: https://am.sourcebmx.com/collections/bmx-cranks/products/jet-bmx-square-taper-race-cranks?currency=cad. They seem available, and in the right length. But I know nothing about BMX parts. Does the square taper fit MTB square taper BBs? As BMX cranks, I have to assume they're burly enough for trail riding. The bonus is I have a bunch of 104 BCD narrow-wide rings still left kicking around... So if this fits, the price is good...

Anyone know about BMX standards and can advise me on this? As I recall @jonKranked has (or used to have) a BMX, and could potentially be going down the same rabbit hole for his kids in the near future...

 

[CrabJoe StretchPants]

Says in the description they fit any standard JIS square taper....so I'd say you're good to go.

 

[stoney]

Components | Spawn Cycles

Spawn Cycles

spawncycles.com

I have Haley on a set of 130mm, iirc.

 

[jonKranked]

So the old school BSA ball retainer bottom bracket and cranks on my son's Commençal keep coming loose. I was looking to replace it with some proper cranks, but couldn't find any MTB cranks that are short enough (I'm looking for a 150mm or 155mm).

Then my research brought me to these: https://am.sourcebmx.com/collections/bmx-cranks/products/jet-bmx-square-taper-race-cranks?currency=cad. They seem available, and in the right length. But I know nothing about BMX parts. Does the square taper fit MTB square taper BBs? As BMX cranks, I have to assume they're burly enough for trail riding. The bonus is I have a bunch of 104 BCD narrow-wide rings still left kicking around... So if this fits, the price is good...

Anyone know about BMX standards and can advise me on this? As I recall @jonKranked has (or used to have) a BMX, and could potentially be going down the same rabbit hole for his kids in the near future...

Square taper is square taper, regardless of discipline.

All my bmx stuff is 3 pc.

There are short crank options out there, most of them are probably bmx.

 

[CrabJoe StretchPants]

Square taper is square taper, regardless of discipline.

All my bmx stuff is 3 pc.

There are short crank options out there, most of them are probably bmx.

Not entirely true.....JIS vs. ISO. Apparently not compatible.

I'm not going to pretend I always knew this....I just googled it.

 

[jonKranked]

Not entirely true.....JIS vs. ISO. Apparently not compatible.

I'm not going to pretend I always knew this....I just googled it.

If you have to resort to square taper you have bigger problems

 

[slyfink]

If you have to resort to square taper you have bigger problems

Yeah, I thought of that. But then I thought it's for a 55lb kid. Should be ok for at least a couple of years...

 

[chuffer]

Watch the "q-factor" / crank to chain stay clearance. If you are using an mtb spindle, you should be good to go. I found that using bmx spindles (profile) on an mtb required a super long (by bmx standards) spindle...

 

[slyfink]

Watch the "q-factor" / crank to chain stay clearance. If you are using an mtb spindle, you should be good to go. I found that using bmx spindles (profile) on an mtb required a super long (by bmx standards) spindle...

good to know. First I was going to scrounge through my parts bin to see if I had an old square taper bb, but then I figured I'd probably be better off with a new one. When looking online, I discovered there are several widths of 68mm square taper bb. Took me a few seconds to figure out that the spindle can be longer or shorter, despite the cups staying at 68mm apart. Anyways, it also seems they are only available in one width at the moment, so perhaps it's a moot point?