[Closed] to ream or not to ream, that is the question

simons_nicolai-uk - Member
We switched from using 30.0 to 30.9 seat tubes on our AM and DH frames when uppy-downy posts became more common. The OD remained the same and I can't see that we've reinforced anywhere else to compensate.

Suspect it will be fine but like Transition I'd not 'approve' it as a mod - ie almost certainly ok but at your own risk.

That's at odds with how I thought Nicolai would do things... I'd have thought making tubes thinner would have involved hundred of hours of German engineering

also some seat tubes are externally butted at the seat clamp area so just because it is thick enough at the top does not mean it will still be thick enough lower down

but measure it up and see..

I say go for it.. nothing ventured nothing gained..

TJ how does increasing the internal dia by 3% cause it to lose 20% of its strength?
Have you run FEA on it then?
Im not saying you're wrong (yet), but im interested to see your workings.

I assume he has based it on the reduction of cross sectional area because it is about 20% loss. Which isn't far off. As a guide, based on standard beam calcs, the loss of stiffness in the reamed length is about 15% and the increase in peak normal stresses in the reamed length are about 16%. Given that its the junction of the top tube and seat stays etc a bit of FEA would tell you more, my hunch is it would probably tell you its worse than the beam calcs. Whether this reduction is significant is down to how much margin there is on the design...

I can't see why you'd weaken your frame and invalidate your warranty just to fit a dropper, when there are loads of 27.2 ones around.

Well my Helius CC has a 31.6mm seat-tube diameter and a 34.9mm seatclamp, can't see it being too much of an issue* if you ream it to take the 30.9mm post.

How snug a fit is the 30mm one anyway?

[i]*I have no experience in reaming of metals and will no way be held responsible if you get a dropper stuck up yer bum [/i]

my Helius CC has a 31.6mm seat-tube diameter and a 34.9mm seatclamp, can't see it being too much of an issue* if you ream it to take the 30.9mm post.

The default tube used at Nicolai is 34.9/31.6. We use a thicker walled tube on the frames for more hardcore use and for XL sizes but the Helius AM, say, is still 31.6 so that's not a weak tube..

How's the riding simon?

Infrequent off road for the last month or so 🙁 but heading somewhere hot and dry for December...

matthew_h - Member

The reaming is not done in one big hit, it is done in stages and the bottom of the reamer is not square to the tube so end up with a graduated step, not too likely to be a significant stress riser.

fairy snuff