broken dahon, broken ankle

[harpoclifty]

I'm new to the forum but now I've broken my ankle I've got a lot of time on my hands.

I've had to undergo surgery to screw a stainless steel plate to the broken bone after falling off my Dahon Cadenza outside sunny Cricklewood station.

Unfortunately, as I peddled off, the saddle, seat post and the top part of the frame snapped clean off around the seat post stay, resulting in me falling to the floor and breaking my ankle.

After the accident the saddle, BioLogic PostPump seat post, seat post clamp and the severed top part of the frame were all still together.
The frame had been creaking in the days leading up to the failure.
My concern is that the design of the BioLogic PostPump will encourage a failure of this nature.

I've been laid up for a month now, can't wait to get the cast off in a weeks time and start riding again.

I would hate to think that someone else could suffer the same fate as me.

Has anyone else had similar experiences with a Dahon Cadenza?

 

[jonny jeez]

Nasty. I was asking about the post pump on another thread so will sit back and await responses.

Hope you recover soon.

 

[RecordAceFromNew]

After the accident the saddle, BioLogic PostPump seat post, seat post clamp and the severed top part of the frame were all still together.

Sorry to hear about your accident. I hope you are recovering well. to the forum BTW!

I had a Cadenza (one with the lockjaw). I sold it and replaced with a Jack not because I thought the frame would break like yours did, but because I couldn't trust the lockjaw to be serviceable long term and I didn't like its lack of a safety catch. I did not take the replacement decision lightly, and only did so after reading every post in the Dahon user forum on that mechanism's adjustment issues. I digress however because I am sure that is unrelated to your frame's breakage.

I am unsure how the PostPump has anything to do with the frame breaking, in that the post's minimum insertion mark is unrelated to the stirrup, and the stirrup is the only thing that makes the post significantly different externally to a normal seatpost, but since the folded stirrup is narrower than the post it should not have any effect on the frame? Also unless I am mistaken the post did not break in your case? Do you happen to have a photo of the broken assembly?

As you probably know maintaining the minimum insertion mark of ANY seatpost is critical, and on top of that I would not like to let the bottom of any seatpost go above the bottom of where the top tube joins the seat tube (which is also the bottom of where the seat stay is welded to the seat tube in pic below). I believe failing to do either or both the above is a recipe for frame breakage like what you described. But for the avoidance of doubt I am not saying that is what you did or didn't do.

 

[harpoclifty]

The main problem is that the distance between the bottom of the post and the top of the stays that join the down tube to the rest of the frame is only 32m when the seat post is at the top of the minimum insertion marks. If you insert the post to the bottom of the marks the overlap is only 24mm.
The top part of the frame above these stays is unsupported tube.
I don't think that's enough and is unsafe. Anyone else with this arrangement please be careful.

 

[harpoclifty]

 

[harpoclifty]

sorry here's a photo

 

[I like Skol]

Given the design of the frame I would have thought a longer minimum insertion would be required to prevent excess leverage at the failure point. Maybe the manufacturer has overlooked this and used stock seatposts with a 'regular' minimum insertion mark.
Having had a standard ali MTB frame develop cracks in that area myself (Seat post was at the Min insertion mark!) I now shy away from running at the min mark or with excessively long exposed seatpost. Better to err on the side of caution and fit a seat post far longer than required so there is a good few inches inserted below the top tube junction.

 

[RecordAceFromNew]

The main problem is that the distance between the bottom of the post and the top of the stays that join the down tube to the rest of the frame is only 32m when the seat post is at the top of the minimum insertion marks. If you insert the post to the bottom of the marks the overlap is only 24mm.
The top part of the frame above these stays is unsupported tube.
I don't think that's enough and is unsafe. Anyone else with this arrangement please be careful.

I can't agree more. This reminds me of a somewhat less than friendly debate I had with certain ex-member who is now thankfully debating elsewhere, presumably. The length of unsupported alloy seat tube above the gusset is rarely, if ever, strong enough to support the seatpost on its own, while creating an illusion to the unwary that could cause frame breakage at best and accident at worst like you experienced. Imho nearly all justifications for such an excessive length of unsupported alloy seat tube are red-herrings - e.g. if it is not strong enough to support the seatpost on its own then it can not possibly contribute to increasing stand-over clearance - it would be the exceptional length (and strength) of seatpost that does it - like a Brompton e.g.

Many mtb frames which have a similar design have a small hole at the back of the seat tube, always below the welds of the cross members IME, to indicate and enable monitoring of the minimum seatpost insertion requirement of the frame (in addition to what the seatpost requires). I can't remember one being there for my Cadenza - I wonder if you might have a valid claim against Dahon IF no such warning is present anywhere.

sorry here's a photo

But that is not a PostPump?

 

[StuAff]

I had a 2007 Cadenza (nicked last year), the first version that had the Lockjaw hinge. And yep, one of those went..
Completely unrelated to this very unfortunate failure though. I have to agree, that doesn't look like a PostPump- unless the rubber bung bit that goes at the bottom is inside the frame somewhere. Dahon posts most emphatically have a minimum insertion point, though this is usually one of the first bits that rubs off with folding and unfolding...

I was a regular on the Dahon.com forums, somewhat quieter these days since the Tern/Dahon split- the new Dahon site, dahonbikes.com, does not as yet have a forum at all. I can't recall reading anything like this happening to any of the Cadenza versions (there were three iterations of the frame design). If it's under warranty, it looks worth pursuing, but I don't know who you'd actually deal with on account of the company split, assorted legal wrangles, change of distribution...
Wishing you a full and speedy recovery.

 

[harpoclifty]

Yes it's a biologic pump post. The screw off plastic cover broke off when the frame snapped.
I should start a campaign to make people check seat post recommended minimum insertion depths and not trust what the
manufacturers suggest.

Unfortunately, I bought the bike second hand and although it's less than 3 years old the Dahon warranty is void.

I'm talking to Dahon direct, who started off friendly but have been radio silent for 2 weeks. The guys at Chain Reaction have been helpful finally hooking up with the Dahon people that I've been talikng to.

Also spoken to Evans Cycles who have been at best unhelpful and at worst patronising. They want to distance themselves from it and don't seem interested, as Dahon stockists, that this seat post may be a problem on this bike.

I think all that I'll have to show for this experience is a steel plate in my ankle, a broken bike and a life lesson.

 

[StuAff]

Not good, sadly unsurprising considering the Dahon/Tern issues (Dahon mk2 have discontinued the bike, Tern's equivalent model is quite different). Dahon have had three different UK distributors in the past five years, so that, too, doesn't help.

 

[Banjo]

sorry here's a photo

Looking at the pic I am no engineer but that looks like an inevitable breakage with so little seat post inserted below the supported part of the seat tube. Probably flogging a dead horse trying to get any help from manufacturers especially as your not the first owner you cant say for definite someone hasnt ridden it even higher.

Hope your ankle repairs itself quickly and good luck .

 

[harpoclifty]

Thanks Banjo, I'm talking to Dahon and they're being helpful so far. I know the guy who had the bike before me, so know seat post wasn't ridden too high, he's not as tall as me.

Only a week to go before the cast comes off.

 

[Banjo]

Thanks Banjo, I'm talking to Dahon and they're being helpful so far. I know the guy who had the bike before me, so know seat post wasn't ridden too high, he's not as tall as me.

Only a week to go before the cast comes off.

Good to hear that Dahon havent just ignored you. Good luck with getting back onn a bike again.I would think initially it will take a while to get your confidence back. I intend to have a good look at the seat post on my Vittesse in the morning.

 

[Old Plodder]

.....just passing through this forum, but had to comment.

Seat posts should have a minimum of 2" inserted into the frame; the frame starts where the tubes are, but it would seem this isn't pointed out these days! (& on longer seat posts it should definately be more.)