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Discussion Starter · #1 ·
Houston, we have a problem!

On my way home from a ride this morning I went over a small (knee high) jump that some kids had made on the track and I heard a crack on landing. It sounded a little different to a heavy chain slap, but since the bike looked and felt fine (no obvious problem) I didn't stop for a proper look at it until I got home 5 minutes later.

On inspection, I found the problem. I seem to have managed get a crack in the outer surface of the vertical strut in the rear-triangle, between the lower pivot and top pivots - see attached photos. It looks as though it might only be the surface that's damaged, but who knows what has happened underneath.

Of course I rang the bike shop, and it seems as though they have a mojo in stock. :) Hopefully once they send my photos off to the Australian importer, and with the reputation Ibis have for customer service, that this will be resolved quicky.

Stay tuned
 

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Discussion Starter · #4 ·
That's good news then, if the replacement is stronger. It's just a question of how quickly that can get shipped out to Australia. I'll get the guy at my bike shop (or Dirt Works) to contact Ibis, rather than perhaps taking the rear triangle off a bike in store.

:thumbsup:

Hans, is the rear triangle the same size on all frames? Mine is a medium, and of course I'd really like to be able to ride next weekend.
 

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is the rear triangle the same size on all frames? Mine is a medium, and of course I'd really like to be able to ride next weekend.
Yep
In the meantime looks like a job for duct tape !
NRBJ (Not really Bad Joke).
Don't let it disillusion (is that a word) you from an awesome bike.
 

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Founder: Dirty3hirties
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2X thickness

hanssc said:
No problem replacing that. Your replacement will have about 2x wall thickness in that area and a smoother finish inside so it's much stronger.
H
Are you fabricating a replacement specifically for him? Or are the rears coming with 2x thickness in that area in general? And why does the smoother finish inside affect strength?
 

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It's the axle
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Notch sensitivity. That's a guess, since I'm not familiar with carbon fiber. A rough surface gives materials a place to start a crack.

Now I'm curious if the entire section cracked, or if carbon fiber material is still one. I thought it was tenacious stuff and not subject to just cracking, fibers and all.

It may even have been a stick or something that got flung at that section by the wheel.

I'm not familiar with the stresses in that location, but my guess is they're minimal. Under high landing loads, the chainstay would be in tension and the seatstay would be in compression, but this section really sees minor forces due to being effectively a pinned member between the bearings. I believe it's there to reinforce and take up forces that would cause the chainstay and seatstay to move relative to one another. Something like that, but a lot more dynamic.

And I apologize for stepping in where someone who actually knows could provide an answer. But this IS the internets!
 

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ddraewwg said:
why does the smoother finish inside affect strength?
Have you ever cut glass or seen it cut? It is pretty difficult to break glass by bending it. But to cut it easily the carpenter etches a very small shallow line. Then a very light bend of the glass breaks it and only along the shallow etching. The glass is much more resistant to breaking when bending while it's smooth.

When something bends it's going to have more concentrated stretch across shallower or thinner areas of a material.

When the surface is smooth there are no weaker areas, the material stretches evenly across the outside of a bend, greatly increasing overall fatigue life.

Polishing and smoothing the surface of materials that are stressed by bending allows use of much lighter amount of material than a rough and irregular finish of the same material.
 

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It's the axle
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I thought I'd post this just because I've never seen anything like it on a Google search. It's an entire book.Oops. It's missing about 150 pages. But there might be answers to questions about carbon fiber characteristics in it.

I just remembered that this crack happened upon landing after a jump. So my external damage idea would only be correct if the strut was already damaged, and the jump just completed the fracture. We may not ever know, unless closer inspection yields clues. And we're all jumping on these bikes. So jumping alone shouldn't be a reason for fracture.

http://books.google.com/books?id=0O...ts=DKPapSA9Jw&sig=7GyVGSNYDVX3ujjmCzcCOzM0esY
 

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details

Hello all,

Here's the background info on that swingarm upright tube:

We had good performance out of the early production parts, then our test riders broke a couple of the upright tubes jumping and we started working on improving the strength. This was maybe 9 - 10 months ago. We figured out that the bladder used was too large and had excessive folding in it to get through that tube.

So, having learned that, we got a smaller bladder in use and also doubled the wall there (added a few grams) just to be sure as we figured that would balance out with the strength of the rest of the rear triangle more evenly. We made prototypes within days and had our test riders try to break them (shuttle runs and big air) Also put those changes into production at that time.
The test riders can't break the current production swingarm uprights with DH racing and jumping style riding. That's what we've been shipping since probably March or April.

In case anyone has a problem with a swingarm or front triangle we keep a stock of spare parts and replace them at no charge if something does comes up. It's not very common considering the number of frames in use. Our goal is to keep people happy and get them back on the trail as quickly as possible.

That's the scoop,
Hans
 

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It's the axle
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It's hard to believe how dedicated you Ibis folks are. It's Saturday, and you're answering forum questions. I love it.

I think I've learned to leave the technical stuff alone, and just ride. Which is what I'm going to do right now. It's Mojo time!


But I'd still like to know the answer. Maybe when the shock bottoms out, then that strut sees more forces. Aargh! Off to ride, I go...
 

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That's the Last thing I wanted to see"CRACK"

Should the pre newer swingarm Mojo owners be worried? Should we replace the swingarm?
It might not happen now? but it may happen sooner or later? I don't like riding thinking that I better not make that jump cause I might break the swingarm?
 

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Wow, that explains why Hans answer is so quick, they have already found that problem, and you guys are offering replacements, how much is the replacement (although I didn own a Mojo yet, but I guess someone might as this question)?
 

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hanssc said:
Hello all,

Here's the background info on that swingarm upright tube:

We had good performance out of the early production parts, then our test riders broke a couple of the upright tubes jumping and we started working on improving the strength. This was maybe 9 - 10 months ago. We figured out that the bladder used was too large and had excessive folding in it to get through that tube.

So, having learned that, we got a smaller bladder in use and also doubled the wall there (added a few grams) just to be sure as we figured that would balance out with the strength of the rest of the rear triangle more evenly. We made prototypes within days and had our test riders try to break them (shuttle runs and big air) Also put those changes into production at that time.
The test riders can't break the current production swingarm uprights with DH racing and jumping style riding. That's what we've been shipping since probably March or April.

In case anyone has a problem with a swingarm or front triangle we keep a stock of spare parts and replace them at no charge if something does comes up. It's not very common considering the number of frames in use. Our goal is to keep people happy and get them back on the trail as quickly as possible.

That's the scoop,
Hans
Awesome.....that's what I like to see.....proactive action by the company. Makes me feel a lot more at ease knowing that not only did i buy a great bike, but that I bought it from a great company.
 

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Ibis CS

God I love this company! These guys really care and they definately make the best bikes. They are so helpful when I call them and I always get to talk to one of the principals. I had such a great ride on my Mojo today!
 

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I can vouch for the quality of customer service. I had a crack in exactly the same place on a March produced frame. I sent Ibis a photo and had a rear triangle direct to my door in the UK within 2 weeks, and in Guinness Foam!
To my mind, small companies that are engineering high-tech kit need to rely on customers for some part of the testing process. This is only acceptable however if the customer service backs this up when problems arise, and clearly in Ibis' case it does! Top marks boys!!
 

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I had a similar issue in the same place.
For the record: Ibis took care of me to the extreme. Fixed the problem ASAP even though I was on the road in the middle of a week-long trip. The inundating barrage of sh!t I took from my buddies over breaking my frame was tempered by the amazement over Ibis' CS. They were a little leery about carbon, but my confidence is restored thanks to Tom Morgan, the Man himself who answered the phone when I called the company.
Thanks again Ibisians!
 
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