Broken seatpost

[JohnCKirk]

Coming home tonight on my Brompton, the seatpost snapped in half! Fortunately I'd just joined a cycle path (on the pavement), otherwise I would have been going downhill on the A40 when this happened, which could have been a bit ... exciting.

Here's a photo of the broken pillar:


I didn't notice anything wrong with it beforehand, but maybe I just don't know what to look for. Are there any particular warning signs, or is routine replacement the best bet? This pillar has done me 8600 km (over 5000 miles), so I've got my money's worth from it, but I'm a bit worried that I might not be so lucky with the timing if it happens again.

[Gearoidmuar]

I've not had that happen to me but I've had the seatpin bolt fail a couple of times. I learnt that this is caused by overtightening.
What happened to you was the cause of the death of a former nextdoor neighbour of mine when I lived in Dublin in the late 70's. He was an American and he fell on the back of his head and died a few days later, after his seatpin snapped.
What make was yours? (I don't know what make his was).

[JohnCKirk]

This is a Brompton telescopic seatpost. The main stem (which broke) is steel. The top stem (still intact) is titanium, which they don't anymore: it's just steel or aluminium now. I can see the problem, since the folding mechanism means that the saddle has to be very high up relative to the frame, so effectively my weight is pushing on the end of a long lever. However, the weight limit is 110 kg and I'm lighter than that, so it shouldn't be a problem.

[alicej]

Ouch! Have you contacted the manufacturer?

[gilesjuk]

I would definitely embarrass the manufacturer into sending you a new one.

If it's aluminium then this shows why you can't have much flex in alu, it just fatigues and snaps. Steel is better.

[snibgo]

Yikes. If you post a close-up of the broken edges, folk here who know about metal might suggest what has happened.

[JohnCKirk]

Sorry for the delayed reply; here's a photo of the broken ends:

(I shrank it down to fit the screen, but I can upload a higher resolution version if anyone would like it.)

As for the manufacturer, Brompton make it pretty clear on their website that they won't deal with the public directly - they only talk to dealers. I'll try talking to the shop I bought it from, but I don't know how sympathetic they'll be after 3 years. I've now replaced the stem, but the new one seems a bit smaller than the last one. If I screw the clamp up tightly enough to stop the stem/saddle swivelling around then I can't use the trigger to actually fold the bike! So, I probably need to go to the shop for advice anyway, but I suspect this will involve being without the bike for a few more days so I'll put up with it for now.

[LollyKat]

From the Brompton site:

Before you contact us please check our FAQs section - there is a good chance that the information you require will already be posted. If you have a problem with your bike, your local Brompton Dealer should be your first port of call.

I can understand how this would apply to routine "problems" but you have just suffered a major and potentially life-threatening failure. I would definitely contact them, politely but firmly. They need to know about it asap, for instance in case the post was one of a duff batch.

[Gearoidmuar]

The post appears to be very thin at one point. This is a manufacturing fault, I would imagine.

[simonineaston]

Brompton made it, not the dealer! I wouldn't have any hesitation in contacting them directly about this serious manufacturing fault... I have contacted Brompton directly myself several times and can reassure you that I have received appropriate responses every time.

[alicej]

Yeah I'd've thought they might want to deal with this one themselves. Contact details are

Brompton Bicycle Ltd
Kew Bridge DC
Lionel Road South
Brentford
Middlesex TW8 9QR

T: +44 (0)20 8232 8484
F: +44 (0)20 8232 8181

Would be interested to see their response.

[stewartpratt]

The post appears to be very thin at one point. This is a manufacturing fault, I would imagine.

I think that's an optical illusion. To my eyes it look slike the fracture surface is not perpendicular to the tube axis; on the left-hand specimen it is raised at the tube's inner surface and correspondingly on the right-hand specimen it is lowered at the inner surface. This combined with the angle of the camera may make it look thinner in some parts.

More than that is difficult to be certain without knowing the lighting, but it looks like a clean fatigue which has started opposite the notched part of the fracture, and the notch was the last bit to go. It's again hard to see in the photos but there's nothing I can see which indictaes a material defect. Looks like simply a fatigue limit which has been reached. 5000 miles on a thin-walled tube which is cantilevered to the extent required by a Brompton? Doesn't sound unreasonable.

It's a while since I did this stuff, though.

this serious manufacturing fault...

If it's not wandering too far into semantics, it's bit early to assume a "serious manufacturing fault" IMO. Clearly it's a failure, which isn't ideal and could have had consequences, but it's not necessarily attributable to the manufacturing.

[JohnCKirk]

Thanks all - I phoned Brompton, and they recognised how dangerous this could have been. Apparently the seatpost counts as part of the frame, so it's covered by their 5 year warranty. So, if this happens to you, take the bike back to the shop you bought it from and they'll replace the seatpost free of charge. In my case I've already bought a replacement stem, but I may go to the shop anyway for them to take a look.

Brompton also asked me to email them some photos (which I've done). They may want to see the seatpost itself, in which case they'll pay for the postage. The guy on the phone emphasised that this is very rare, but I think he'd like to find out what went wrong just as much as me.

[stewartpratt]

If you don't mind me asking...

Not 100% familiar with Brompton stuff, but I assume in your original picture you're holding the post upside-down, ie the flared end stops the post being pulled up too far and the rubber foot is designed to contact the ground when the bike is folded?

The fracture looks to be only, what, 3" or so from the bottom end? Surely that would be inside the frame, well below the clamp?

Just curious as to where that fracture point sits when in use. The place you'd expect it to break is where it enters the frame but I'm having trouble picturing how that part of the post ends up at that point.

[Tonyf33]

scary stuff, I've never had a seatpost failure even with ultra lightweight titanium seatposts. As you say though the extra leverage because of the extension out of the frame is likely to be a large factor.