My bike broke in half......

[Smudge]

What makes you think its a rebadged Dahon ?
I've never seen a Dahon with a frame like that, or a Tern come to that. I know Tern had a spate of their folders breaking at the main hinge, but this was after they parted from Dahon.

 

[RoubaixCube]

A bit of FlexGlue™ will solve that.

 

[FrankCrank]

The bike was bought locally here, place of manufacture unsure, and I presumed it was a Dahon clone as Sunzone throws up virtually no info, Dahon were/are the biggest manufacturer of folders. I also heard of Tern having similar failures. The flexing I think was a combo of the folding/rising stem, and the frame design itself. I would be happy to ride a steel folder, but not aly after this. My R20 is a non folder, but will fit in our Jazz no problem. Anyways, it's not something I want to dwell on, just draw a line under it and move on. As I said - a heads-up to anyone with a similar bike.

 

[classic33]

We were on hols in Koh Chang when it happened. I take a morning ride a few miles to a posh resort and plonk myself on a sunbed for ten minutes or so. When I got back on the bike and started pedaling, that's when it gave way. Luckily nothing hurt but my pride, and no one saw it, and it was the last day of the hols. Left the bike lying there in disgust whilst Mrs Crank was summoned to rescue me in the car. She took ages getting to me as it was quite early. The resort is exclusive for Russians, and by now a few were up and walking past giving the bike strange looks and wondering what happened. Anyways, I'll strip the bike of all its parts and recycle them onto another project. I've got a Raleigh Twenty here that'll be my new travel bike - over engineered and built to last, they knew how to make a sturdy bike back then that's for sure

PS - The break looks clean, no track of failure. With steel you get some warning of imminent failure, but aly is different, and then there's carbon

I'd say it's the weld that has failed, not the frame tube.

 

[Low Gear Guy]

This design of bike puts a lot of stress at that part of the frame. Very few folders of this style are used for significant distances and are usually seen pootling around caravan parks and along the seafront. I think you have basically worn the bike out after ten years use. For regular use of a folding bike the steel Brompton is more sturdy.

 

[Smudge]

To me it looks like a generic no name folding bike, of which many are sold in supermarkets, market sellers on Amazon or Ebay, or box shifters on the net. They are the BSO's of the folder world. Dahons are much better made than folders like this, in their frame design and manufacturer. People have extensively toured on Dahons and rode around the world on them. But on alu folders, particular attention needs to be paid to the fold mechanisms, they need to be maintained and adjusted correctly so there is no play in them. But that wont help poor manufacturing and poor welding such as you often get on no name bikes.
I'd say you did well to get 12 + years from this Sunzone.

 

[SkipdiverJohn]

To me it looks like a generic no name folding bike, of which many are sold in supermarkets, market sellers on Amazon or Ebay, or box shifters on the net. They are the BSO's of the folder world.

Whenever I acquire anything bike-shaped to ride, the first thing I do is make sure the frame is made of steel. I only get ali framed bikes as scrappers to strip for parts, never to ride. The frames always get binned. Single downtube folders are the worst possible structural design, and the folding flange joint is going to be subjected to massive numbers of bending stress cycles every time the tyres go over bumps, or the rider accelerates or brakes. Steel is the only material that can be trusted to survive that sort of loading without fatigue failure. I'm surprised the ali frame lasted as long as it did, TBH. You wouldn't catch me riding an ali frame with only a single tube keeping the two halves of the bike apart.

 

[Smudge]

Whenever I acquire anything bike-shaped to ride, the first thing I do is make sure the frame is made of steel. I only get ali framed bikes as scrappers to strip for parts, never to ride. The frames always get binned. Single downtube folders are the worst possible structural design, and the folding flange joint is going to be subjected to massive numbers of bending stress cycles every time the tyres go over bumps, or the rider accelerates or brakes. Steel is the only material that can be trusted to survive that sort of loading without fatigue failure. I'm surprised the ali frame lasted as long as it did, TBH. You wouldn't catch me riding an ali frame with only a single tube keeping the two halves of the bike apart.

Obviously a folder, by its very design, isn't going to be as strong as a normal bicycle frame. But if you need a bike to fold thats what you have to have. Also not all alu framed folders are created equal, you get well made ones and crap made ones. In fact that goes for any alu framed bike, folder or not. Plus steel framed folders like Brompton aren't exempt to breaking, incidences of that can be found.
I'm quite happy with alu frame bikes and i've not had one break yet in decades of cycling.

 

[SkipdiverJohn]

I know steel can and does fail; I had a 28 year old Raleigh hi-tensile frame crack a chainstay last year. It gave me some warning though as it felt "funny" to ride for a short period before it actually went. I still managed to complete my 16 mile round trip on it even after failure two miles in, just by using a fairly low gear and not putting too much force through the pedals to minimise flex. What I don't like about alu (or carbon fibre) is that it is prone to sudden failure without much if any warning, which makes failure potentially more dangerous. I was taking it easy and keeping my speed down on my old hack bike when it failed, because I had a feeling something wasn't quite right.

 

[Gunk]

Don’t worry it’ll polish out 😂

 

[FrankCrank]

Thanx for all the replies folks. Been busy since I got back from hols and not had a chance to strip the bike of parts and take a closer look. Initially it seems like a weld failure rather than the adjacent tubing, and the the weld itself looks very neat superficially. My (sizable) gut instinct is the frame design itself is not good, as mentioned by others, it puts all the loading right at the main frame hinge. I think the reason I got a dozen years from it is because of using it as a travel bike, ie taking it in the car to wherever, rather than a daily plodder. When I first got the bike, I'm sure I read that Sunzone was a spinoff of Dahon, they were becoming very fractious at the time due to 'internal differences'. Anyways, it was yonks ago and memory all a bit fuzzy on that. Apologies to all Dahon fans if I got that bit wrong. If I see anything else under the magnifying glass worthy of mention I'll do another update, but for now thanx again for some great feedback

 

[presta]

I know steel can and does fail

The difference between steel and aluminium is that steel has an endurance limit, and aluminium doesn't.

Steel will tolerate and unlimited number of stress cycles if the stress magnitude remains below the endurance limit, but with no endurance limit, aluminium will always fail eventually, no matter how low the stress.

 

[A V Lowe]

Taiwan companies offer a pick & mix of frames & parts like this

Aluminium alloy (no one uses pure Al) is a eutectic - mainly of Al & Cu which has weak grain boundaries that present no resistance to crack propagation, unlike steel - filled with filthy carbon & carbon-iron (perlite) which will give ages of creaking & flexing before the residual section can no longer carry the loads, so you can 'see' key clues, like paint flaking off where the substrate has cracked, or rust stains, where water has got in.

I avoid Al parts wherever possible from the picture there is a dark area (corrosion?) where there may have been a scratch or nick that presented a stress raiser from which the crack grew. Welding = HAZ = local changes in material structure = high risk of crack generation. Presumably the first frame you've snapped. I've lost count...

 

[12boy]

I also prefer steel, although I have 3 Al bikes right now, a Cannondale mtn bike, a Fuji flat bar road bike, and a Xootr Swift folding bike. I don't think they will fail anytime soon but they are not made like the OP's bike. I have never had an Al stem, handlebar nor seat post break either. A Dahon Speed P 8 is chromo and a used one should be fairly inexpensive if a Brompton is too spendy. Those old Raleigh 20 are pretty cool too.

 

[FrankCrank]

Taiwan companies offer a pick & mix of frames & parts like this

Aluminium alloy (no one uses pure Al) is a eutectic - mainly of Al & Cu which has weak grain boundaries that present no resistance to crack propagation, unlike steel - filled with filthy carbon & carbon-iron (perlite) which will give ages of creaking & flexing before the residual section can no longer carry the loads, so you can 'see' key clues, like paint flaking off where the substrate has cracked, or rust stains, where water has got in.

I avoid Al parts wherever possible from the picture there is a dark area (corrosion?) where there may have been a scratch or nick that presented a stress raiser from which the crack grew. Welding = HAZ = local changes in material structure = high risk of crack generation. Presumably the first frame you've snapped. I've lost count...

Yes, first frame I've snapped, if it was me you referred to? Actually, the Raleigh Chopper I had as a kid needed a repair weld carried out, but it wasn't snapped in half. Quite a big gap between snaps
Got the frame stripped now, married the two halves up and looks like a very clean break, with no obvious flaws or trigger points (photo may be deceptive). I can weld stainless and mild steel, not alu, not that I'd even attempt to in any case. Just keep it as a conversation piece The Raleigh Twenty I have here is from '77, and I have another in UK from '80 awaiting modernisation. Both are non-folders, but I think it says something about the longevity of steel.