I realise I'm opening a can of worms here, but bear with me. I'm genuinely unsure what to do, so feedback is appreciated.

My hardtail has a UN73 square taper BB and Raceface Turbine crankset on it. The shifting has been bulletproof even through 3 winters on one cassette, chain and chainring set, and I've been a long-term square taper fan. I also have a new set of 4-arm Middleburn RS7s ready to stick on there.

The thing is, the reason why I need the RS7s is that the non-drive crank has rounded off its taper – it's the second successive one to do that in the space of about 3 years. I'm obviously not keen to round off another new crank (RS7s aren't cheap, after all), so I'm seriously thinking of investing in a decent ST BB – Phil Wood would set me back about £90-100 or so – with the idea that getting the cranks properly fitted would reduce the chances of rounding the NDS crank. I also need to get some 4-arm chainrings for the RS7s (my current Turbines are 5-arm).

I've never seen the point of outboard bearings, and been fairly anti them (we fear change…), but doing the sums has given me a bit of a wakeup call: £100 for BB plus £60-70 for the chainrings is enough to buy a new XT chainset. The way I ride seems to make me prone to rounding off NDS cranks – I've been told that riding right foot forward when standing on the pedals backs off the crankbolt infinitessimally, which over time causes the crank to shift on the BB taper. Obviously a decent BB and proper fitting *should* sort that out, but at that cost I'm not sure it's worth it.

So, thoughts?

Obviously a decent BB and proper fitting *should* sort that out

I've never heard that a high end BB will cure this problem. You may just be "too much" for ST.

I'd add that xt rings will be nowhere near as good as middleburn.

No easy answer!

I feel your pain in the last 6 mths have managed to round off 2 nondrive side middleburns and one White Industries non drive side on differant bikes both SS right foot forward man here!

I'd add that xt rings will be nowhere near as good as middleburn.

True, but when I finish the rings that come with the XT crankset, I can just buy some more solid replacements.
I think it's more the proper fitting that I would hope should sort the rounding problem. But as postierich says, it's not just me that suffers from this 🙁
I think inexorably I'm shifting towards outboard bearings… Again, when they break I can replace them with a more durable BB (Hope, Crank Bros or the like)

I agree as nice as the middleburns are.
for the money I would buy an xt set up now though
the new middleburns for outboard bottom Brackets are nice
but prob a lot more than you want to spend at the mo

Rounding off cranks tends to be as a result of loose crank bolts. When you fit the cranks, DO NOT grease the axle or crank itself, but use threadlock on the bolt thread and apply plenty of torque. Then just check that your bolts are still tight before every ride (or carry an 8mm allen key in your Camelbak if you're that worried!)

: P

Sorry, should have added – Phil BB and Middleburn cranks here, they're flippin' lovely. 🙂

: P

Ye-es… I see where you're coming from, but believe me, over the course of the last 3 years I've done that – threadlock, no grease, lots of torque, tightening the bolts every ride where necessary. I'm reasonably on the ball mechanically, so it's hard to believe that I would miss something grossly wrong, but still the cranks get rounded off.