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Hi, a few days ago I only knew where my bottom bracket was, now I know about BB92, BB71 (same thing?!), spindle diameters etc etc.

But I'm confused, firstly I'm finding it next to impossible to find a crankset for my BB92. The bike is a RM Thunderbolt with a 92mm shell.

Eg, go to https://www.jensonusa.com/Cranksets?MultiValueCrankBBInterfaceType=BB92 one is $500 and the other is boost.

I saw this https://www.bikesandbeyond.ca/product/shimano-slx-crankset-52345-1.htm which apparently is BB71 which is the same as BB92?! But isn't 71mm a shell size?

It just seems really hard to shop for cranksets because there's no easy way to filter based on shell size (the one thing that cannot change).

I hope that doesn't read like a rant, I suppose what I'd like to know is, what's the trick for finding cranksets and is BB92 just not catered to anymore? I gather BB30 might fit, but is the spindle length of the crankset going to be right?

Thanks
 

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Bb92 is your bottom bracket type. You just need a crank with a 24mm spindle. Or dub, but then you need a dub bb too.

Look at Shimano cranks. They sell them in different arm lengths, and that's it. They fit whatever bottom bracket you have.

Raceface cranks have weird spindle lengths to fit fat bikes, but that's something else.
 

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^^^ yeah. It is kinda complicated. You can BB92 bottom brackets to fit 30mm spindles too, so really anything from 24/22 GXP, 24 through (Shimano et al), DUB, and 30mm through. The bearings are pretty thin on 30mm spindles. I just got one for my power meter cranks. Most all mtb specific cranks have the appropriate length spindle for normal MTB spacing.

Here's a decent explainer. Scroll below the video:

https://www.worldwidecyclery.com/blogs/worldwide-cyclery-blog/what-size-bottom-bracket-do-i-need

Go to the Wheels Manufacturing website and check out different BBs.

https://wheelsmfg.com/bottom-brackets.html
 

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BB71 isn't a bottom bracket standard. It's Shimano's item number for a specific bottom bracket.

https://www.amazon.com/SHIMANO-SM-BB71-41B-PressFit-Bottom-Bracket/dp/B007FOR200

BB92 doesn't require anything special from the crank side of things. It's basically the pressfit version of the venerable threaded bottom bracket from a width standpoint (92mm is the width of a threaded bb shell plus the bb cups).

All Shimano and SRAM mtb cranks will work fine with it. Cranks with 30mm spindles can work with it, if you have the right bottom bracket. But as Lone Rager says, there are limitations.

Boost spindles complicate matters some. SOME frames with boost rear hub spacing will work with a standard chainline. Others won't, because of frame clearance issues (I have one of these). Some manufacturers like SRAM make all their mtb cranks with the same spindle length, and achieve boost chainlines with chainring offsets. Shimano doesn't do it that way. Shimano uses the same chainrings, but the cranks get either standard or boost spiders to adjust the chainline. Some companies like RaceFace can use either boost chainrings or boost spindles, or can further fiddle by flipping the chainrings over.

For you, OP, to keep things simple, just buy either a Shimano or a SRAM crank and a pressfit bottom bracket to fit the crank from the respective company. If your frame is new enough to have boost hub spacing, then buy the boost variant. If not, buy the standard version. This will probably make the chances of encountering incompatibilities about as small as they possibly can be.
 

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Even considering boost, that's usually in the chainring spacing.

There's a lot of acronyms, but it's mostly for the bb.

30mm cranks in bb92 scare me. I know it's out there, but damn. That's a tiny tiny bearing.
 

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Even considering boost, that's usually in the chainring spacing.
Everybody does it differently. you're thinking chainring offsets because that's how SRAM does it. I was wrong about shimano doing it at the spindle. Up until the current generation of cranks (12spd, direct mount), Shimano has done it at the spider.

30mm cranks in bb92 scare me. I know it's out there, but damn. That's a tiny tiny bearing.
I have thousands of miles on such a setup. Not all of the compatibility bb's are worth a damn. IMO, the only one worth using is the flanged bearing that presses directly in the frame that can be bought from a variety of companies like Enduro, Hope, etc (it's the same bearing, though). Eliminating the cup typical to BB92 systems allows for the bearing to be more or less normal-sized.
 

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I personally have not seen any BB92 x 30mm BBs that have sleeves. RaceFace, Hope, Wheels Mfg, Enduro, E13 all have flanged bearings that press in directly. Some, if not all, are dual row bearings. But, yeah, tiny balls.
 

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I personally have not seen any BB92 x 30mm BBs that have sleeves. RaceFace, Hope, Wheels Mfg, Enduro, E13 all have flanged bearings that press in directly. Some, if not all, are dual row bearings. But, yeah, tiny balls.
who was talking about sleeves?

Race Face's bb92x30 bottom bracket has cups and bearings pressed into the cups. TINY balls. They also use a sleeve between the cups to seal out moisture, though I didn't find it useful. I have one that I burned up fast. The Enduro/Hope/Wheels/e13 do not use cups. The balls are quite a bit bigger than what RaceFace sells. They last a LOT longer (I've been getting 3x-4x the life that I got out of the RaceFace).

I can take pictures of old ones if you want photographic evidence of the difference.
 

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Thanks, understanding that they're pretty much all the same spindle length was the missing piece.
There are occasions where spindle length can differ. It's important to be familiar with them.
1. road cranks (shorter spindles than mtb cranks)
2. fatbike cranks (WAY longer spindles)
3. Race Face mtb cranks and others with modular spindle designs (can come in a whole lot of lengths, and boost spindles are an option sometimes)
4. Downhill cranks (based on 83mm bb shell frames, which can occasionally appear on bikes that aren't downhill bikes)
 

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Hey guys, let me revive a 2 year old thread, please. I have a P.slope advertised with a BB30 crankset. I ordered BB30 / 68/73 Raceface cranks, and low and behold, the spindle is a full inch longer than the (stripped) cranks that are on the bike. I'm assuming that's because there are no outboard BB cups on this bike, as the bearigs are within the 73mm shell. What I can't figure out is what to replace it with. There's very limited information on differing spindle lengths. Thoughts?
 
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