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

That's a lot to take off!What's the wall thickness?
Being a transition its probly about 5mm!

dunno 🙁

Shims

What size seatpost clamp?

shims...the metal is not thick enough to withstand the removal of 4.5 mm IMHO. you would be removing over 50% of the metal if not it all IMHO.

dunno 2010 bottlerocket

tricky one!
will you be raising and lowering the post in the frame too? or is the 125mm adjustment gonna be enough for all your riding? if the latter I'd probably go with a shim (despite absolutely hating seatpost shims)
reaming for me would depend on how much seattube material there is and how low it needs reamed to.
I'd ask Transition's opinion?

junkyard we're only talking 0.45mm here

Junkyard - 0.45mm!

Ok let's assume it's 34.9mm.That makes the wall thickness 2.45mm. Ream 0.9 mm and the wall thickness is 2mm which is 20% less. Which is a lot.

So it has a 34.9mm seat tube clamp. There are plenty of frames that use a 30.9mm post with a 34.9mm seat clamp (specialised being one)

I'd guess transition specced it with a 30mm seat post for a bit more material and a bit extra strength, personally I think you'd be ok.

If it's decent aluminium and the seatpost isn't super extended when you are pedalling I'd ream it - PITA to do tho.

ST will likely be the same diameter on the outside - 34.9mm

davidtaylforth - Member
I'd guess transition specced it with a 30mm seat post for a bit more material and a bit extra strength, personally I think you'd be ok.

Or cos it's crap alu?

Or cos it's crap alu?

All Alu is crap, steel is real and titanium is magic.

I'd be tempted to ream it Tony, it's only 0.9 off the diameter, maybe ask Surf sales and see what they say 😉

How much would you get away with taking off the dropper post?
Maybe take the frame halfway to one of the more obscure sizes (not sure which actually exist but I imagine there is a 30.4 or 30.6 out there somewhere?)

Also if its the 27.2mm route, then you could always try lightly sticking the shim inside the frame somehow, keep the post/shim greased a little and it should stop there?

EDIT:
[url= http://www.chainreactioncycles.com/Models.aspx?ModelID=6257 ]30.4mm posts[/url] if you wanted to ream halfway with the frame and want a normal seatpost for some reason. Would still need to take 0.25mm out the walls of a dropper post though

There's an easy solution:

turn the 0.9 seatpost down to 30.0.

SImples! 😎

If you do just don't sit down too hard 😀 its been done before I've seen a picc some where.

Al will glue one on for you.

hmmmm maybe 27.2 and shim then 🙁

Jedi, we've (at 18 Bikes) have done exactly that a couple of times on Bottlerocket frames perfectly successfully. There's plenty of material as the frames are so overbuilt. Just find a descent LBS or machine shop and they shouldn't have any trouble at all

really? oh that is rad! 🙂
if i cant find someone local i may pop up. how much?

sounds wrong to ask for a reaming 🙂

Yup, done a couple of frames at least. It needs to be done slowly with an adjustable reamer, before using the 30.9mm reamer to get a good job but isn't difficult as such.

Probably be about £20 or so depending on how long it takes

is it a book it in job or turn up and chill for a couple of hours?

Would be better to give us a shout before turning up so we can make sure we have the rights tools at the shop rather than the frame-building workshop

I tried so hard to get the decimal point tin the right place as well 🙄 and 😳

Personally I would say its far too much to ream out and you will leave a stress raiser at the bottom of the reamed out section.

I(t might be OK but you are removing a significant amount of strength

Have you got the post yet? I have a 27.2 GD 4" remote post and will be acquiring a new 2nd hand frame with a 30.9 seat tube.

If you have a seatpost of similar or equal radness we could swap or PX and all reamage gets avoided 😀

TJ, the seat tube on a Bottlerocket is hugely over built and is massively thick. There is plenty of room to ream out to 30.9mm without troubles. As for stress risers, I can't see how that would happen at all, especially with careful reaming.

You can get a custom made longer shim from [url= http://wheelsmfg.com/content/view/529/41/ ]wheels manuf[/url].
I would defo go 27.2 + shim.

You would get a step - a change in cross section where the reamer does not reach.

Overbuilt or not - removing 20% of its strength is a lot.

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.

Ah well, we'll let the ones we've done in real life speak for themselves

Think I might be inclined to believe what the frame builders/modifiers are saying (18 bikes) on this one 😉

I'd ream it but I think it was an oversight by Transition. It should have had a 30.9mm seatube from the factory, especially as it's designed for what it is.

lars from transition says deffo dont do it 🙁

Go on do it, bet they're updating it for 2012/13 so would be a good excuse for a new frame 😈 😀

It's not like you're doing massive jumps or anything 😉

To be fair no manufacturer in the world is going to say ream my seat tube*

*unless you were wasted at interbike or something

To be fair no manufacturer in the world is going to say ream my seat tube*

*unless you were wasted at interbike or something

Remind me never to get wasted at interbike...

Jedi, keep your eyes peeled. I will be listing my GD this/next week in the classifieds dependent on when the replacement arrives.

I need cash at the moment so I'm swapping it for a less exciting 30.9 upper downer.

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.

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.

How's the riding simon?

ream it! im sure Graeme will understand and give you a new one if it goes wrong (maybe in your 'decorators radio' paintjob too 😉 )

Jedi - pop into HARRIS Motorcycles in Hertford, they possess all the aluminium working tools and knowhow you could ever want, and then some. They've been helpful in the past for me.

http://www.harris-performance.com

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