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I currently have a RF SixC 30mm axle crank on my weenie 29er, with a BB92 pressfit BB. I'm going through BBs too quickly though.
I've tried Rotor (£26) and Hope (twice that) and nothing lasts more than a few months, as the bike gets used quite a lot (and I'm not over-preloading them, before you suggest this...). This is due to the shonky design, which is clearly a bad one as there just isn't enough space for the bearings when you mix BB92 PF with a 30mm axle.
One option is to go back to a 24mm axle (say XTR) but I like the SixC cranks. So... here's an idea.. I'm considering trying a DUB BB and reducing the diameter of the cinch axle by 1mm from 30mm down to 29mm, on my lathe, to fit. Okay, the axle will be weakened a tad but the bike doesn't see anything more gnar than a towpath so I doubt this is a big issue.
Has anyone heard of such a thing? AFAIK the DUB BB will be the same width as the PF41 so it should fit.
The RF axle is pretty old anyway so I'm tempted to try it just for fun.
Interesting idea!
I find the RF BBs not too bad so long as you whip the inner seals off and pack with grease before installing. I get 12 months on a mtb. Hope ones have terrible sealing imo.
Given the 30mm axle has no rider weight limit, I’d infer it could cope with a 120Kg rider bashing down a DH track. So probably a fair bit of headroom for your use-case
Plus you’re only removing 0.5mm material
I’d go for it and report back whether you lived or died in a month or two 🙂
I've not found dub Bbs to be any better than GXP tbh. Still mad keen to loose all their grease over the winter and rust, despite the 'extra seals'
Ta. I've ordered a DUB BB so I'll have a play over the weekend and report back (unless dead).
Hopefully more BB manufacturers will start making DUB BBs too - is it just Sram at the moment?
Hope make a DUB conversion for most of their 30mm BBs.
Yeah, I spotted that too. Their PF41 30mm BBs are not long-lasting though, so I'd recommend anyone with the same setup as me to avoid them.
So far I've seen CeramicSpeed ($$$$), Kogel($$$), CBear ($$), Enduro ($$) and Wheels Manufacturing ($$$) that do PF41 (BB92) for a DUB axle.
PF41 30mm BBs are not long-lasting though
Far from a hope specific problem, its trying to squash in an axle which was never intended to fit, so the bb is pants because the bearings are naff because they're too small. But you know that hence looking at DUB. Equally I wouldn't expect improvement from DUB, the shell is just not designed with axles and therefore bearings that big in mind.
Going from PF41/30mm to PF41/DUB means you're going from a 5.5mm deep bearing to 6mm - hardly a massive improvement. As said, PF41 wasn't designed to take a 30mm spindle.
Going from PF41/30mm to PF41/DUB means you’re going from a 5.5mm deep bearing to 6mm
Whats the point of DUB then?
Just another standard to flog?
Isn't the dub NDS seal and preload keyed to the NDS spine keying/spline
So, machining the spindle down is great but you'll be abandoning the sealing ability of the BB so shortening the life span further than then already disapointing sram standard.
Ben from Bird Bikes has commented on here recently that DUB BBs are the longest lasting BB they've ever used.
Whats the point of DUB then
A single axle standard suitable for all bottom bracket shell standards. Its a reasonable and sensible idea.
Given the point of comparison for sram was their gxp bottom bracket which has the sort of life span Dolania Americana would be embarrassed of, DUB was only ever going to offer an improvement, even in the case of pf92 for which it's a bad solution.
The issue is that you need something long enough to accommodate things like bb30 as well as 68mm bsa so it pushes you away from 24mm because of the odd bearing size you'd end up with.
I'd be wary of machining down a cinch axle as it attaches to the crank arm on a taper if you have to take some material away from the taper you may end up with a wobbly crank.
Ben from Bird Bikes has commented on here recently that DUB BBs are the longest lasting BB they’ve ever used.
And I still don't know anyone thats replaced one although all of those would have been threaded. No one I know & have asked uses a PF one.
We'll, there's me.
I swapped out my first one yesterday, but it's actually been languishing in the garage, knackered since early May. Installed September 2018.
The only thing I didn't do is my usual 'crack it open and fill with grease' on install.
I’d be wary of machining down a cinch axle as it attaches to the crank arm on a taper
Yeah, that's the key. I've measured the taper and it's very close to 29mm at its fattest, so it's marginal. Obviously only one side will be affected but I'll need to do some careful measurements before I crack on with the machining.