Frame Snapped

C

Curtech

Member
Region
USA
Riding to work and suddently things got way too bouncy! About 6mo old. About 1500km on paved roads. Seems aluminium may not be a good choice for bike frames. Anyone else seeing this happen?

IMG_9453copy.JPG
 
My $600'ish dollar Amazon special MTB is aluminum, about 45 pounds, and is going strong after 4 years, used daily. Actually a darn good entry into e-bikes. I think you have an unfortunate anomaly.
 
That sucks to happen on such a new bike. How did it get too bouncy? Speed bumps? Was there a previous crash involving that bike? What kind of bike is it?
 
Curtech said:
Anyone else seeing this happen
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I had it happen on a Marin Stinson on the seat tube. They put the minimum insertion line too small on the saddle tube. It was above the top tube yet below the seat stays. It wobbled and broke the frame. I removed all electric, that was not material to the issue. And brought it to the dealer as a bare frame. I was then sent a new bare frame for free. The dealer had to document sawing the old frame in half. I then ordered a much longer seat post. If you are within the weight limits of the frame, you should get a new one. If it is just a crappy frame design it might happen again. Steel frames are faster and laster than carbon in the real world.
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That's your Mukkpet Ninjer? I see a ridiculously huge cutout on the left side of the downtube. Probably generated a stress fracture if the picture is accurate.

The frame tubes also look like the skinny and stylish tubes seen in a steel fream to me. Yet this is alloy?


mukk.jpg
 
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Slaphappygamer said:
That sucks to happen on such a new bike. How did it get too bouncy? Speed bumps? Was there a previous crash involving that bike? What kind of bike is it?
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The boucyness is from the frame brake. Maybe I should have said it got springy feeling in unusual and sudden ways. I was on paved road. Just the usual bumps from patches and the like. No crashes. Mukkpet Ninja.
 
PedalUma said:
I had it happen on a Marin Stinson on the seat tube. They put the minimum insertion line too small on the saddle tube. It was above the top tube yet below the seat stays. It wobbled and broke the frame. I removed all electric, that was not material to the issue. And brought it to the dealer as a bare frame. I was then sent a new bare frame for free. The dealer had to document sawing the old frame in half. I then ordered a much longer seat post. If you are within the weight limits of the frame, you should get a new one. If it is just a crappy frame design it might happen again. Steel frames are faster and laster than carbon in the real world.
View attachment 193176
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Weight limit of the bike is 330lbs. I'm 165 so no issue there.
 
Some people pay the scrap metal price for their mini e-motorcycles and then are surprised they had bought junk.
Experiencing a battery fire was the other option.

Curtech said:
Seems aluminium may not be a good choice for bike frames.
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Aluminium is a perfect construction material for bike frames. Scrap metal is not.
 
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Without the details it looks like the downtube is too small and the battery too high. Almost like in an afterthought override the marketing department suits said A Bigger Battery Will Sell More! Without discussing with design or engineering or anyone who has ever worked on bikes. This most often happens with scooters. Designed to sell online, not to maintain. They are garbage, return to Bezos at the nearest hole foods, even if you don't get money back to be made Whole.
 
the light on the fracture is not very good, but from what I can see this did not snap in one go, there are some more darker and even fracture lines which could indicate that the fracture started there and the more violent structures with lighter color gone in one go. This area takes a lot of stress, and there is also a cable port on the other side and the hole for the battery mount. It might look like it started to crack from the inside right next to the weld on the driveside
 
Stefan Mikes said:
Some people pay the scrap metal price for their mini e-motorcycles and then are surprised they had bought junk.
Experiencing a battery fire was the other option.


Aluminium is a perfect construction material for bike frames. Scrap metal is not.
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the right Al is,the older imported cast items were often junk porous castings,new forged or drawn Al shouldn't have this problem I have a bouncey bike now I am getting scared to ride( think it was the "pogo" fork though) any time you see a defect in AL stop using or get repaired Al is not intrinsically bad it just needs to be treated right( no pun) all those marvelous fuel gulping behomeths you see marring the skies are basically aluminum( they are fairly safe.)
 
Thats generally how aluminum fails. Welding heat weakens metal so they generally break somewhere near the weld (tubes are usually butted, so they tend to crack where the thickened area ends; this is true on steel frames as well). Aluminum needs to be heat treated after welding to restore its strength. My guess it either the tubing had a defect that allowed a crack to start or it wasn't properly heat treated and thats a high stress area and was the first to fail.

Properly done aluminum frames last functionally forever. Its not an issue with the material itself. Like all things, defects happen and its possible to screw up the design or build it poorly. Hopefully theres a warranty you can take advantage of.
 
harryS said:
That's your Mukkpet Ninjer? I see a ridiculously huge cutout on the left side of the downtube. Probably generated a stress fracture if the picture is accurate.

The frame tubes also look like the skinny and stylish tubes seen in a steel fream to me. Yet this is alloy?
Click to expand...

Yeah, those tubes look awful wimpy for an alu frame. Aluminum has basically no fatigue limit, so if frame design allows it to flex it will eventually fail. Thats why aluminum frames generally use large diameter, thin walled tubing; makes for a very rigid frame that avoids that issue.

The cutout right at the highest stress point of the frame also seems like an issue. It may not have failed through the cutout but the cutout likely allowed some frame flex in that area. Every time aluminum flexes it looses strength (unlike steel, which has a certain amount of flex it can absorb without loosing strength).
 
Looking at your first picture, it cracked right where the tube met the steerer column, and 1/4" from the cutout. Ah well, you probably should get a new bike out of this from the mukkpetters , but do you want to ride it?

Can you give us a picture looking down on the tube? It must be wider than it looks. Probably a wide oval?
 
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