Square Taper Round Off Prevention

[legrandefromage]

My torque wrench was always set to 42 just to make damn sure nothing would work loose when 'just riding along...'

second hand cranks can be a minefield and can often be bought blind - I have been very lucky/ jammy so far.

As for arguments as to which is better - just check out the latest 'standards' and you will see that no-one can agree on anything as there so many! There were quite a few premature external BB failures but that may have been due to owners' budget choice over quality.

 

[mikee]

allen key bolts , its easier carting an allen key round as opposed to a 14 mm socket and bar

i tend to find that greased cranks take longer to settle in
and can lead to loosening off
so clean everything and assemble dry

 

[dyna-ti]

Square Taper Round Off Prevention. Any ideas on what crank bolts to get and methods to stop it working itself lose all the time . Cheers

As a devout hater of square taper, go splined and hollow axle, it's so much stiffer you won't believe the difference.

Personally i find this a little nonsensical[no offence to the poster ]
Square taper is a hardened steel axle,believe me it isnt going to flex no matter how heavy you are or the riding style.
Most of the others are based on a hollow tube that in no way can be compared strength wise with a solid bar :?


Its also now understood that external BB's wear a hell of a lot faster than sealed BB's the like of which from shimano weve been using from the dawn of time

 

[gtRTSdh]

Square Taper Round Off Prevention. Any ideas on what crank bolts to get and methods to stop it working itself lose all the time . Cheers

As a devout hater of square taper, go splined and hollow axle, it's so much stiffer you won't believe the difference.

Personally i find this a little nonsensical[no offence to the poster ]
Square taper is a hardened steel axle,believe me it isnt going to flex no matter how heavy you are or the riding style.
Most of the others are based on a hollow tube that in no way can be compared strength wise with a solid bar :?


Its also now understood that external BB's wear a hell of a lot faster than sealed BB's the like of which from shimano weve been using from the dawn of time

I don't want to get into an argument, but it's clear which one of us isn't an engineer.

 

[dyna-ti]

Square Taper Round Off Prevention. Any ideas on what crank bolts to get and methods to stop it working itself lose all the time . Cheers

As a devout hater of square taper, go splined and hollow axle, it's so much stiffer you won't believe the difference.

Personally i find this a little nonsensical[no offence to the poster ]
Square taper is a hardened steel axle,believe me it isnt going to flex no matter how heavy you are or the riding style.
Most of the others are based on a hollow tube that in no way can be compared strength wise with a solid bar :?


Its also now understood that external BB's wear a hell of a lot faster than sealed BB's the like of which from shimano weve been using from the dawn of time

I don't want to get into an argument, but it's clear which one of us isn't an engineer.

Sure OK show me the formula showing the differences
Talk is cheap

 

[MikeD]

For a BB spindle we're interested in torsional stiffness -- the spindle has to carry all the torque from the left crank across to the chainrings, and if you're coasting with pedals level every bump is twisting the spindle. Big drops even more so. Torsional stiffness is proportional to the polar moment of inertia -- I'm not an engineer but if I've got the sums right the moment of inertia of a "new style" spindle (24mm tube, ~2mm wall thickness) is over twice that of a square taper one (17mm bar). If it's made out of the same stuff it would therefore be over twice as stiff.

I'm not getting into the "greasing tapers" argument

 

[Chute55uk]

i kinda thought a hollow tube was torsionally stiffer than a solid bar (something to do with surface area)
just my 2 penneth

 

[MikeD]

If they're the same diameter, a bar will be stiffer than a tube. But for the weight of a thin bar you can make a fat tube, and stiffness increases as the fourth power of diameter so a little bit bigger = a lot stiffer.

 

[gtRTSdh]

For a BB spindle we're interested in torsional stiffness -- the spindle has to carry all the torque from the left crank across to the chainrings, and if you're coasting with pedals level every bump is twisting the spindle. Big drops even more so. Torsional stiffness is proportional to the polar moment of inertia -- I'm not an engineer but if I've got the sums right the moment of inertia of a "new style" spindle (24mm tube, ~2mm wall thickness) is over twice that of a square taper one (17mm bar). If it's made out of the same stuff it would therefore be over twice as stiff.

I'm not getting into the "greasing tapers" argument

You can see in this thread that the cartridge BB shaft is not a constant diameter all the way along, the diameter reduces by circa 4mm where the bearings sit. This also gives a fantatstic visualisation of how far away the end of the shaft is from the bearings.

http://www.retrobike.co.uk/forum/viewto ... 35&start=0

So with square taper and shimano cartridge, the shaft is effectively a cantilever from the bearings outwards, supported by a much reduced diameter, and the torque from the left hand crank is transmited through the smaller sections.

If they're the same diameter, a bar will be stiffer than a tube. But for the weight of a thin bar you can make a fat tube, and stiffness increases as the fourth power of diameter so a little bit bigger = a lot stiffer.

Yes, precisely.

DynaTi, send me your E-mail I'll send you some of the maths I've done, in hand written PDF's. I'll so some sums on this later but I've got to go to antenatal classes tonight.

 

[MikeD]

You can see in this thread that the cartridge BB shaft is not a constant diameter all the way along, the diameter reduces by circa 4mm where the bearings sit.

I was simplifying for the sake of, er, simplicity