seems to me that the seatpost should be well past the locknuts thing ?

Sorry to hear that you crashed and glad you were not more seriously injured.

Looking at the pictures of your bike, that frame isn't cracked , but it would appear that there is way too little seatpost/sleeve insertion into the frame.. that sleeve that is shown as broken should be further into the main tube at least 3" or better than is shown .. the seat post q/r should be basically sitting on the two jam nuts, and then the seatpost should be inserted appropriately so that there is proper insertion..

I'd want to know why there is that much sleeve showing .. as your bike appears to be a 2009 or older, I don't know if the seat tube parts are available from Montague, but if they were, and assembled properly, the bike could be safely used again..

Sorry to hear about your crash, but I'm curious how this seat tube failure caused it since you mentioned you were able stand up on the pedals as the seat started giving away. Did the seat jam the rear wheel?

I'm curious because I too sometimes worry about my folders failing, and want to know what to expect. I once forgot to lock the mainframe joint on a folder and hit the ground faster than anything I ever experienced (and I'm a lifelong skier, skater, skateboarder) - very scary. All my other "fall" experience seems to have given me at least a moment to brace for impact.

That's not a frame failure, it's a crappy seatpost causing the seatpost & insertion area to bend/break. It's still an issue for the Montague company to address, since it's obviously their seatpost. I'm just hoping you didn't get injured.

Someone modified the bike from original design.. that is not a Montague problem .. that would be on whoever modified the bike .. probably going for more seat extension .. check out how it should look..

hmmm. i'm happy to say i don't know anything about these bikes but, it does seem as though that seat tube insert is adjustable and can be seen in swissbike models as well as in other models across the montague line. in every one of these pictures you can see that the extension piece is standing proud of the maintube by approx. 100mm which is minimum insertion length for bicycle seatposts. this seems like a dodgy arrangement since at 100mm the seatpost will not be inside the maintube and all the leverage is solely on the extension (as is seen in the op's pics).

"The Montague frame cracked at the place where the seat tube meets the hinge nut."

He wrote that the frame is cracked. Although to be honest with you, I 'm trying to figure out what's happening here.

The seatpost has a natural extension and the upper nut works like a locknut on a classic headset, I suppose. Presumably there are specifications for the piece that say how much it can be extended.

I'm glad the OP is ok, however this post feels like blackmail. I do not appreciate that.

Thanks
Yan

Looks like it was the seatpost which broke.

Don't understand how the seatpost braking led to your being propelled you forwards out of the bike. Not questioning it, just trying to make sense of it.

Have you considered replacing it with a 'little bitty' Dahon?

Top of the tube holding the seatpost appears to have snapped. Was it designed to hold the seatpost by itself or did the post need to be embeded another 2 1/2 or 3 inches?

Seat tube failures (or cracks) at the base of the extended mast are becoming all too common.

IMO- this is a poor design and has always been despite it's current popularity. It's an especially poor design in aluminum, and my comments apply to almost all aluminum frames with extended masts, not only Montagues.

There are 2 main things owners of these frames need to know.

1- the seat post must extend at least 1-1/2 diameters (about 2") below the top of the highest cross brace, ie. top tube or seat stays. If the post doesn't extend that far, all the load is borne by the unsupported seat tube which isn't strong enough. Unfortunately, many owners are misled by the minimum insertion mark on the post, because they're not told that that mark is only about the post, and may not apply to extended mast frames.

2- even if the post is deep enough (more than 2" below top tube), there's no assurance that the mast won't fail. Seat posts are flexible, as is the mast, and if the post is not rigid enough, it won't reduce flexing of the mast, which will fatigue over time. When depends on the rider weight, saddle height, and ride conditions, but all are likely to fail there eventually (eventually can be many years+).

The bright side is that if the post extends deep enough, the tube will crack over time and the likelihood of a sudden catastrophic failure is low.

So, in fairness, it's impossible to blame Montague without knowing if this is the original post and what their instructions say about insertion depth.


BTW- the above is my opinion, and not everybody agrees with me (obviously), but I'm not without knowledge of metals and structures, so it's not a totally uninformed opinion. I offer this qualification to avoid getting drawn into a back and forth debate.

The Montague manual for the pre-2009 Swissbike (with jam nuts below the post clamp) specifies a minimum of 2 1/2" seatpost insertion into the main frame, confirming what you have posted as a general rule of thumb.. the pictures in the manual show the seatpost clamp sitting very close to the main frame body .. the failure in question shows no seatpost insertion into the main frame, and consequently a fail..

I've had Montague Paratrooper/Hummer for a decade used as a mountain bike and now as a mid-drive e-assist mountain bike, I still contend that there was a setup or adjustment error, maybe unintentional, but the result was still unfortunate. These bikes are very rugged.

Ok, this thing has been bothering me .. to the point where I took my Montague apart to check it out.. the short answer is the OP's frame (pivoting rear assembly) is indeed shot .. there are no serviceable parts to correct the break ..


After viewing way too many Paratrooper pictures it appears that there are two lower pivoting triangles that were used, and from what I could make out from pictures , not related to being 18" or 20" models, although it would make sense that the 20" sized frames would have the longer seat tube .. and, there is nothing height adjustable to screw up ... so the main seat tube is continuous from the top of the clamping area to the bb .. the tube is roughly 35mm od, with a bore of 27.2" and a post clamp diameter of 32mm..

My new contention is that I could see breaking a Montague frame with the longer seat tube (as the OP's bike clearly has) if the actual seatpost didn't actually go down through the 32mm od part of the seat post and get into the main frame (2 1/2") where there is complete support (like on mine, an 18" frame) .. this would make minimum insertion markings on normal seatposts irrelevant unless you were a knowledgeable bike person .. not knowing what length seatpost was supplied as original makes an after break assessment difficult, but I could easily now see a costly mistake could be made.. as yet, I have not read anything from Montague addressing this.. could be out there, just not something that I have found..

Now I'm going to put my bike back together..

b-but, that's what i already said...

Looks like there should be a "minimum instered seatpost mark" painted on the bikes frame. Like peopel have said it is easy for a person who do not understand bikes to use the minimum mark on the seatpost as a guide. Also I think a lot of peopel throw the user manual away when they throw the box and packing material- or at least misplace it.

Yes, but the discussion was on the older, nutted frames (like the OP has), not the newer ones .. Since I had a 'nutted' frame, I took a look to see if there was anything that could be done.

In this case, the user manual would have been of no help as it is vague at best. It also only shows the frame that I have when addressing seatpost insertion, but not the frame the OP has.. that's not good ..

Sorry, off the grid for the weekend. Yes, these pictures look just the way my bike did, with the sleeve standing 3 inches or so proud. I never adjusted the sleeve. Didn't know you could, actually. I assumed that if I didn't raise the seatpost farther than the safety line I would be fine. btw, my seatpost is the original one that came with the bike.

In retrospect I should have thought more about the practicality of the design. An extra 3 inches of seatpost would have been enough to insure rider safety.

I had a cargo rack with a single pannier that contained my work clothes and lunch. On this kind of frame there's nowhere to attach the front of the rack except to the seat tube. (See attached) The whole thing, seat rack and pannier fell back dragging the rear sideways in a quick motion that left my front wheel sideways to my line of travel. All speculation on my part. It happened in a flash, and I slammed into the ground. The sight of that front wheel cocked sideways is the stuff of nightmares.

Another aluminium failure, would it have given some signal if it's steel? I now hope my seat post and handle post is steel as well(mine is a dahon like folder in steel). Maybe that's why there is almost (?) no Brompton failure?