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Broken bottom tube: why?

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Broken bottom tube: why?

Postby StridaD on Mon Jun 28, 2010 10:39 am

Hi all

I would appreciate any engineers' (or similar experts') opinions about this.

As the subject states, the bottom tube on my Strida 5.2 recently broke. The interesting thing is, the break looks extremely similar to the fracture suffered by the fake Strida, as posted by Amuro on another thread (http://www.stridaforum.com/forum/viewtopic.php?=5&t=413&p=4639#p4606). Same place, just above the front weld where the pedal bracket is welded to the bottom tube.

After the break occurred, the steering pin onto which the bottom tube is locked was no longer vertical. It was angled back towards the rear of the bike, about 45 degrees or so from the original position. But it was still so tight that I could not budge it. It appears undamaged.

So I was wondering what could have caused this. Would the tube have cracked and thus put pressure on the pin, causing it to budge? Or would the pin have budged, causing the tube to crack? And as for the pin, how could it have budged when it seems so tight? And why is it even movable anyway, wouldn't it be better if the pin were also welded in place? Is it even possible to achieve 20-25 Nm with a normal Allen key?

I assume that this is a rare occurrence, as I haven't found any other such reports on the 'net. But I do hope this doesn't point to any sort of inherent flaw in the design.

As an aside, I would like to thank and praise Strida Europe for their excellent customer service, they very promptly honoured the frame warranty after seeing photos and I received a replacement bike within a week. Interesting to see the differences between the LX and the 5.2, but that's another story. :D
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Re: Broken bottom tube: why?

Postby nindyz noisy strida on Mon Jun 28, 2010 12:58 pm

Hi StridaD

What symptoms did you find before the tube broke?
Hope it didn't go whilst you were riding.

I have had numerous problems with my Strida, and have battled with getting it right again after taking it for a service at one of only two distributers in the UK.

One of the things this company did was spin the "BB" around (i think thats what it is referred to, i would refer to it as a crank, though i might be wrong!!), the reason they did this is because the crank would not tighten up and keep loosening, therefore the belt would always be loose (had no problems for 8 months before this service).

Since they have done this , the bike unfortunately has not been the same.

I had originally taken the bike in for a broken spoke on the back wheel, but i thought id get the service done at the same time, my mistake.

The back wheel was never trued properly, and had been back to the same place several times with broken spoke in a very short period of time.

I quite recently bought a set of 18" wheels, with the metal freewheel, as i had enough of broken spokes, but now im facing a new problem, im now hearing a squeaking noise from around the crank/pedal area.

QUESTION:

Could this be

A) My Metal pedals making the noise
B) The bottom tube about to snap
C) the "BB"(crank) giving up due to more pressure being exherted due to the upsize of the wheels?

Any answers would be great, i do love my Strida, thing is i have not owned it from new (bought on eBay) and im not sure i'd be covered for the frame if it was damaged.

Unfortunately, It has of late been giving me more pain than pleasure.
nindyz noisy strida
 

Re: Broken bottom tube: why?

Postby nindyz noisy strida 2 on Mon Jun 28, 2010 1:07 pm

Forgot to mention that i found the pin bracket to be loose and had to tighten it aswell.

Regards

nindyz
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Re: Broken bottom tube: why?

Postby StridaD on Mon Jun 28, 2010 3:09 pm

Hi nindyz

It did happen while I was riding, but fortunately at low speed. There were no prior symptoms.

Sorry to hear about your problems. No disrespect intended, but perhaps you would like to consider asking the mods to move your post to its own thread? It wasn't my intention to start a discussion about general problems here. Indeed, I regard my incident as a freak occurrence and I am just curious more than anything else about what people think. And as I said before, I was very happy with Strida Europe's customer service, so I don't want to lump them in with any distributors whose own customer service may be sub-par!

Thanks for your understanding, and good luck.

StridaD
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Re: Broken bottom tube: why?

Postby Ed on Mon Jun 28, 2010 8:03 pm

Could it be that during the weld they had too much heat on the tube which weakened it for the long run since you said it's around where the bottom bracket was attached?.

Might be human error because all stridas are hand made and not by machine I found out. On my bike i've been commuting daily with it for a year so far (12km a day) and everyday I stand on the pedals straight up to do a stretch near the end of my spin. So far I didn't notice any fatigue or even a crack on my bottom tube yet. It's a pretty beefy tube so it should withstand quite a bit. I'm 155-158lbs though so I doubt i'm putting enough stress on it.

Not that i'm saying you are heavy at all! :wink:
and keep us updated on how the new tube is working out for you! stand on it and give it some stress to see how it's working. Just no bunny hops and jumping :)
Ed
 

Re: Broken bottom tube: why?

Postby Amuro Lee on Tue Jun 29, 2010 12:04 am

StridaD wrote:As an aside, I would like to thank and praise Strida Europe for their excellent customer service, they very promptly honoured the frame warranty after seeing photos and I received a replacement bike within a week.

Hi StridaD,

Could you post the photos here?

Thanks! :wink:

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Re: Broken bottom tube: why?

Postby StridaD on Tue Jun 29, 2010 11:48 am

Ed wrote:On my bike i've been commuting daily with it for a year so far (12km a day) and everyday I stand on the pedals straight up to do a stretch near the end of my spin.


My commute is roughly the same distance, also daily. Did it for over 1-1/2 years on the 5.2.

Ed wrote:I'm 155-158lbs though so I doubt i'm putting enough stress on it.

Not that i'm saying you are heavy at all! :wink:


Hah! :P Heavier than you, but not that much. Approx. 85 kg, so well within official Strida tolerances!

@Amuro: OK, your wish is my command! :)
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Re: Broken bottom tube: why?

Postby Amuro Lee on Tue Jun 29, 2010 12:46 pm

StridaD wrote:@Amuro: OK, your wish is my command! :)

Thanks StridaD! :wink:
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Re: Broken bottom tube: why?

Postby Ed on Tue Jun 29, 2010 9:48 pm

Your weight is waaay below spec of 220lbs. I'm just looking at your pics and wondering how in the world did that break there. It feels as if pedal stress broke it, but it's not like you can stand on this bike and mash the pedals with your entire weight. at least you have gotten away from the breakage with no harm. Hopefully this is just a one off thing and it's the first we've heard about it on an real strida out of the 8-10 years they have been selling the strida 3-5's from Ming.

I'd expected the wheel axles to break before the bottom bar. But the axles seem to be holding out alot of my abuse from sidewalk/road riding and hopping those curbs (1-3 cm rise only! :) )
Ed
 

Re: Broken bottom tube: why?

Postby Human_Amp on Thu Jul 01, 2010 11:04 am

Looks like a doggy weld to me ... ie the crack comes from the weld which may have been badly done resulting in a microscopic crack where the weld joins the tube - such cracks can make a tube MUCH weaker. Maybe it was a rooky welder ? , who's work was not 100% checked - maybe robot welding would be better ? (but there again many bike companies promote 'hand welded' as an advantage).

At least Strida Stand by their frames, with good guarantees and replace any faulty ones - good result.
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Re: Broken bottom tube: why?

Postby Amuro Lee on Wed Mar 09, 2011 6:05 pm

It happened to a Taiwanese Stridanut when he was riding in Shanghai.
Image Image

Another Taiwanese Stridanaut also found a crack on the BB mounting of his Strida.
Image Image Image

Photos source:
http://strida.kuso.com.tw/modules/newbb/viewtopic.php?viewmode=flat&topic_id=5146&forum=6
http://en.wikipedia.org/wiki/Amuro_Ray

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Re: Broken bottom tube: why?

Postby TomT on Wed Mar 09, 2011 6:17 pm

Sounds like you'll need to check out Ming's frame warantee :roll:

I hear they are good at customer service and will 'do good by you'. When Dahon frames break, they seem to ship out a new frame and then you have to pay for a mechanic to swop over all the bits. So just to be sure I'd ask Ming for a complete now bike.
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Re: Broken bottom tube: why?

Postby Ed on Wed Mar 09, 2011 8:30 pm

It seems to be all breaking around that part of the tube. could it be a bad welding job that stressed that joint there?? I better check mine before I start riding in the beginning of my season in April just to make sure everything is tip top. If I ever see a crack i'll call up ming and hopefully they can mail me a new bottom tube with that new BB that has a massive weld all around it. :).

We've had far less frame cracks than the other major folders it seems (dahon, brompton, bike friday(recall fix)) they where all on the seatpost which we don't have such a design.
Ed
 

Re: Broken bottom tube: why?

Postby tightfisted on Fri Sep 30, 2011 12:46 pm

Just been offered a replacement bike after suffering this failure for the second time on my Strida 5.0. (Tube replaced under warranty the first time) I've had the bike for 2 & 1/2 years.

Interestingly, the second failure was preceded by a persistent creaking from the bottom bracket area. I couldn't see a crack though until the tube failed catestrophically (for the bike not me). Inspection or the failed tube shows dirt on some areas of the broken surface so I must conclude the were fine cracks present for some time. If your Strida appears to be creaking from the bottom bracket, inspect these weld joints very carefully.

In my opinion the walls of the bottom are to thin and the welding process has created a weak point.

While waiting for a decision I've been thinking about reinforcing the bottom tube by filling it with Epoxy Resin filled with glass bubbles to form a syntactic foam. Clearly this would invalidate the frame warranty but should prevent this failure at least. I can't think of another way to reinforce this tube without introducing stress points elsewhere.

I've been told that the replacement bike, Strida SX, is "an improved version with an EN Standards frame." I can't find any mention of EN standards in the 5.0 manual or at Strida.COM. If the bottom tube on the new frame has been redesigned and is genuinely stronger I won't need to worry about modifying it...
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Re: Broken bottom tube: why?

Postby Blackstridaaustria on Fri Sep 30, 2011 1:15 pm

Hi tightfisted,

many thanks for your report.

tightfisted wrote:I can't find any mention of EN standards in the 5.0 manual or at Strida.COM.


We have here some pics of the EN reinforcements.

EN 14764 City and trekking bicycles - Safety requirements and test methods
STV@gmx.org
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