just wondering as i have a posh one coming, thanks
This much
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If they're that posh, they should say what torque setting to use if you're that way inclined.
How posh can it be to outweigh the advantages of external BBs?
How posh can it be to outweigh the advantages of external BBs
Personally I've yet to find any *convincing* advantages to external BBs...
My old square taper crank/BB weigh about the same, bearings last longer, they're more tolerant to not having perfectly faced frame, they're cheaper and the marginal stiffness difference in the real world all contribute to the reasons why I'm still using SQ taper on 8 out of 11 bikes.
+1 amedias - well said! 😉
generally to about 30ft/lbs - or until you’re nose bleeds which ever comes first - just popped a set of Middleburn RS7 uno on the SS - learning the expensive way about not tightening up far enough
amedias - MemberPersonally I've yet to find any *convincing* advantages to external BBs...
HT2 cranks are dead easy to take off - and you're not relying on a fiddly little thread to do so.
What amedias said. Still running a pair of Middleburns and a Royce BB on the singlespeed, wonderfully smooth and stood up to several years of abuse and more torque than I'd normally put through gears.
There's likely to be a torque setting written somewhere in the paperwork that comes with the cranks. If not, somewhere around 40-50Nm is normal. Remember to grease the threads of the bolts _only_ - DON'T grease the axle / tapers of the cranks, there's practically no risk of them seizing together and they're an interference fit so you're best off tightening them properly, taking them for a ride or two and then checking they're still tight. If you grease the tapers, you risk over-tightening the crank bolt and pushing the cranks too far onto the axle, which may start them splitting.
Oh, and make sure your crank remover is properly screwed in (not cross-threaded and tightened fully) before trying to remove any cranks! Stripped threads mean the crank will be a b*tch to remove...
: P
How posh can it be to outweigh the advantages of external BBs?
hollow laughter :o)
the torque is 50Nm which is roughly your full weight on a normal allen key about 10cm long 🙂 (allowing for the finite width of your foot)
lol i should have known 😉 well i guess i meant really how far on the spindle if that makes sense. i quite some time ago fitted a set and tightened up enough to make the bb flush with the inside of the arm flat inside. it was nice and tight but worked loose in the end and then would never go on right again
How far on just depends on the chainset - some sit further onto the BB axle than others.
I find HTII stiffer, and lighter.
But then, I'm clearly some kind of freak 🙂
I find HT2 a bit stiffer and a bit lighter but I'm quite seriously considering converting the one mtb I've got HT2 on back to square taper as I've got the cranks spare and I know the BBs will last longer.
Anyone want a set of XTR 970 cranks?
I also forgot to mention Q-factor on External BB cranks, and as for the 'it's dead easy to remove them' - maybe you should spend more time riding your bike instead of taking it apart 😛
"it's dead easy to remove them" is handy if you have to keep replacing the bearings... 😉
: P
I find HTII stiffer, and lighter.
I find sq. taper well cheap (UN26 £5.50) and I've never bent one
But then, I'm clearly some kind of freak
unquestionably :o)
"it's dead easy to remove them" is handy if you have to keep replacing the bearings...
ah - touché!
amedias - Member
maybe you should spend more time riding your bike instead of taking it apart
sod off you luddite!*
X x X
(*please read this with your sense of humour activated)
my sense of humour is always activated 😉
back tot he OP...
ightened up enough to make the bb flush with the inside of the arm flat inside
that sounds like it was a stretched crank as it should never have gone on that far, which is likely why it came loose again.
and I've never bent one
Stiffness is not about bending them, it's about power transfer. I noticed when going to HTII.
When I was speccing insurance replacement bikes, I looked aruond and the XTR of the day (2007) was the lightest option, and they were also on offer at CRC 🙂
it was new ;-( i think i streched it i kept going as i figured it should be flush it wasnt til after i thought that it probably shouldnt lol
Stiffness is not about bending them, it's about power transfer. I noticed when going to HTII.
unless the crank warms up it's transferring all the power...
unless the crank warms up it's transferring all the power...
No it's not. Some of it could be just going to help you lift your trailing foot back up.
Well the most obvious reason for external BBs is that they give people no excuse to come out with rubbish like:
Remember to grease the threads of the bolts _only_ - DON'T grease the axle / tapers of the cranks, there's practically no risk of them seizing together and they're an interference fit so you're best off tightening them properly, taking them for a ride or two and then checking they're still tight. If you grease the tapers, you risk over-tightening the crank bolt and pushing the cranks too far onto the axle, which may start them splitting.
The ironing being that it's the retightening after a ride or two which results in over-tightening, rather than the greasing (which simply ensures a correct installation, given it's the elastic forces in the taper which should limit how far they go on, not friction).
No it's not. Some of it could be just going to help you lift your trailing foot back up.
I guess physics is not your forte ?
Just found instructions 40nm then go for a ride then redo at 40nm. Now just to find out what 40nm is lol
You could guess, but you'd be wrong. I might just be so much better at it than you that what I say seems silly but is actually correct.
You were thinking of a pretty simplistic model. I'm saying it's more complicated and your energy could be wasted in all sorts of ways - being put into stresses and strains in all sorts of directions which likely would not find their way back to the chain - but it's too complicated to model in one's head I imagine.
You could guess, but you'd be wrong.
So the silly comment about lifting the trailing foot up was a deliberate attempt to give the impression you're more stupid than you actually are?
It was to suggest one of many possible places the energy could go, without having a thorough analysis of the problem.
As an aside, why is everyone on STW constantly banging on about how absolutely utterly stupid everyone else on STW is? Doesn't that get tiring after a while?
Back on topic, stiffness is desirable for power transfer. I suspect that bike/crank designers have done more than waffle on a forum for a few minutes in designing their stuff, but I could be wrong.
I'm saying it's more complicated and your energy could be wasted in all sorts of ways
such as ? Assuming the crank flexes but doesn't heat up, the power you allege to be lost has to go somewhere else and I want to know where
Well I am talking about possibilities, not hard facts - since I understand Physics so well 😉 I can't pretend to be able to do FEA on cranks I haven't seen in my head.
But why don't we share ideas on the subject and have a pleasant discussion instead of this 'you're stupid' stuff?
For starters - the BB area flexes under hard pedalling, which means the spider and drive side crank are no longer aligned perpendicular to the chain and pedalling forces. This could maybe cause the spider to flex laterally with respect to the crank, and it's hard to see how the recovery of this flex would end up propelling you forwards. The energy that doesn't go towards the wheel would end up flexing the spider and various other bits of the crank to and fro - going to potential energy and then back into non-useful kinetic energy. A fair bit of it would end up as heat but so well distributed throughout the crank you wouldn't feel it getting warm. Could be all sorts of vibrational energy going all over, it's too complex of a problem to model with any useful degree of real-world applicability.
I guess that's why they invented FEA 🙂
FEA Flexing Each Atom?
There are some thoughts on bottom brackets on
http://www.highpath.net/
under Cycle information
"Square-taper bottom bracket
There are two versions of this design. Both have 2° tapers but JIS (Japanese) ones are slightly fatter than ISO (European) ones; this means that a crank goes further onto an ISO axle than a JIS one. However they can often be mixed so long as each crank mates with at least 2/3 of its axle taper without bottoming on the end."
To wade in here... I used to think square taper was the way forwards, but I ruined too many NDS cranks, and in the end just decided to fit HT2 cranks and wash myself thoroughly afterwards. I still feel dirty for doing it, but they haven't busted yet.
I can't pretend to be able to do FEA on cranks I haven't seen in my head.
but that's only about numbers, I'm talking conceptually. My point is, there is very little hysteresis in steel or aluminium parts in elastic bending, so they cannot absorb energy
Pretending it's too complex to model is just a smoke screen 🙁
but so well distributed throughout the crank you wouldn't feel it getting warm
you cannot store much energy in non-apparent vibrational modes except at the molecular level where it's called heat...
To be fair molgrips does have a point, though it's not the one he thinks it is. The trouble is, he seems to be coming at this from the perspective of knowing about physics, without actually apparently knowing some of the important details - apologies if you do actually know enough materials science to understand sfb's point about hysteresis of metals. This is a very fundamental point, which means that however much FEA you might do, and however hard it might be to see how the recovery of flex is going to help propel you forward, if the input energy isn't being dissipated as heat, which it isn't to any significant extent due to the low hysteresis, then where other than propelling you forward is it going?
In theory there have been suggestions that energy due to flex is dissipated in the legs of the human attached to the bike, though I don't think anybody has proved this point. Anecdotally, Sean Kelly won lots of sprints whilst riding one of the noodliest frames ever seen in the pro peleton.
Suggesting energy is dissipated in lifting up the trailing foot is still a really stupid point, which adds nothing to the discussion, and doesn't particularly suggest you have anything useful to add.