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Hit me up if you need anything. I have that TPU ready to go on my printer if you need parts printed.
Hey Ryan, is there any way to run analysis or estimations of wrapping a rear end in carbon like greg minnar did on the Norco?
How much wrap is needed to make a change? How m thinking about trying this on my steel rear end to mitigate some wag and wallowing feel.
Hey Joe, It's hard for me to model that in FEA since I'd need a more advanced software to do that. But what you can do is start with the carbon you have available and wrap one or two layers around your tube, then go ride it. If you still need more stiffness, add another, and so on. What sheet are you planning on using?
I really have no idea about carbon so I’m searching. Let me know if you have any advice!
This was a great answer, and super helpful. You can design flex into the tube set itself between the welds to help remove stress from the welds. That makes perfect sense.
When I was a wee lad, we were working on the Diamondback DH frame prototype and it kept cracking at welds. The factory kept making it stiffer and stronger and it kept cracking, and we just kept chasing welds around the front triangle as they added braces or gussets (FYI THIS IS A MASSIVE OVERSIMPLIFICATION IN THE NAME OF BREVITY AND PEOPLE MUCH SMARTER AND MORE KNOWLEDGABLE THAN ME WERE MAKING THE DECISIONS). Your explanation helps explain what I was observing. As a result of how stiff we made it, the bike rode stiff too. It was absolutely punishing when combined with the early Enve carbon DH rims.
This is also why I'm personally curious about flex and cracking, because I've broken a lot of bike frames in my life, frames made many different companies from carbon and aluminum.
A carbon fiber repair kit may be all you need. It comes with all of the stuff. It looks like you can get more carbon from this website too, which you'd probably want.
The mod will look kinda like this: Rough up the surface of the tube so the epoxy can bond to the surface, wet the tube surface, wrap the sheet around the tube, wet the outside of the carbon you just wrapped on, use a heat gun to have the air bubbles expand and pop, wrap the tube in the supplied tape to compress the carbon and squeeze out excess resin, let it cure for the time it says. Remove the tape, do a quick sand, Shred. This YT channel is helpful for tips and tricks about carbon parts.
Bikes are simple but can also be hard. Making a good bike is one thing but making production runs of good bikes that consistently last 10+ years for a consumer is a whole nother game and the hard lessons don't get to be learned for many years down the line.
Let's say you started a bike company now and you made a bike. The bike worked and it seemed to hold up well. Little did you know, in 3 years time all of the chainstays would crack from fatigue... and the frames are still under warranty so you have to replace them all. OH, also you continued to sell that bike for 2 more years before you knew they would break... so here comes 2 more years of failures in your future. Expensive and painful for the brand. You have to investigate why they failed to make sure this doesn't happen again (because if it happens again, you may not have a company anymore... if you were able to survive the first issue) and your hand is forced and you have to get into the engineering of it all, fatigue life, stress distribution, etc.
It'll be interesting to see how smaller bike companies handle this as they become medium in size. I do think this is where engineering service companies like Faction come into play. It may seem expensive to hire an agency to help design your bike, but if you plan to go big, it's way cheaper than having all of your bikes break a few years in.
So how available are FEA tools to your typical bike engineer? When I worked for a product design agency my boss mentioned we were quoted €25k for a seat of legit programme (he saw the built in FEA in solidworks as Mickey Mouse), he also mentioned there was a pay as you go option but it was €1k a simulation or something nuts. I understand how people use solidworks to basically create fatigue maps but modelling a swing arm seems quite sophisticated especially if you’re trying to model in a shock that maybe hasn’t hit the market.
It depends on the company. Big bike brands likely have advanced simulation programs, but as you mentioned, they’re expensive and require time to master to ensuring real-world accuracy.
You can achieve a lot with a simple SolidWorks FEA assembly and a test fixture. If you have a physical test rig and model that same setup in FEA, you can get comparable results using more basic programs like SolidWorks. But in a perfect world we'd all have the time and money to use the advanced models to get that extra % improvement in accuracy and learnings.
The other interesting part I don't see discussed often is that aluminium does not have a fatigue limit. The wording of that is slightly confusing if you don't know what it means, but essentially aluminium will eventually always fail from stress cycling at any stress level after enough cycles. Steel has a limit, where as long as the stress is below it's fatigue limit, it will not fail no matter how many cycles.
It takes quite a while, but generally aluminium cracks around the 500 million cycle mark, at least that's what airframe engineers assume.
If your a boat person you see this in old aluminium dinghys, no matter how well built and designed, the constant force of driving through waves, all the hulls crack, it's an intrinsic property of the material.
I've always assumed that an alloy frame ridden hard will crack at the 5 year mark I'd ridden regularly
Awesome! I watched all the videos from predator and placed an order!
What do you think are some garage tests I can do to measure change before and after?
I thought about this for my testing, and I think the simplest and easiest is a static load deflection test.
Essentially bolt the front triangle to a table, you can even just ratchet strap it down and suspend the rear triangle overhanging the table. Then progressively load the rear axle and measure the deflection.
I figured you could just use some climbers cord fixed to a carabiner around the rear axle, and attach weightlifting plates. Deflection can be measured either as degrees at the table, or with a plumb line suspended off the rear triangle to the floor with a ruler.
I'm not sure how much load you'll need to measure significant deflection, or if any of this can break your frame, so try at your own risk.
I'm sure Ryan knows some of the loads you'd see, so it would easy to calculate how much weight you should hang off.
Measuring roll would be some type of breaker bar setup, which would be a bit more complicated, as you have to induce a twisting force on the rear axle itself
Do you have a big flat heavy surface you could mount the frame to?
Wouldn't take too much to replicate what Joe did in this Starling video.
https://www.youtube.com/watch?v=zto62OypjUk&ab_channel=StarlingCycles
Exactly what I was thinking of doing. I just don't have fancy machining, and also I wouldn't do it with a wheel on, I'd just load the axle directly.
Yeah I'll try and rig up something getto that can be replicated before I add any carbon!
Hey Joe, I'm not sure the motion you're trying to fix is coming from the swingarm.
Where do you think it’s coming from?
In other words the swing arm looks like a triangulated structure. If you are looking for stiffness, I'd look at the main pivot or the bolt on drop outs
That said ,nothing comes across on the intertubes well for me
And perhaps take a look at the down tube to bottom bracket ish joint . I'm just sayin.
Carbon/epoxy twill (woven with as many fibers in 0 and 90 degree orientation) mostly behaves uniformly in all directions. Using an isotropic material with stiffness (Young's modulus) of about 60 to 70 GPa is going to be pretty representative on much easier to simulate.
Simulating how the fabric drapes over a shape is especially important when using materials with fibers all aligned in one direction (unidirectional materials) or when analyzing potential failure points.
In this case, the key factors affecting stiffness are the shape of the component—ie open or closed cross-section, and the thickness of the material. To test this hypothesis, you could perform a sensitivity study by varying the material's stiffness, let's say 25% and comparing different cross section shapes.
Good job on these article by the way! you're sharing very technical knowledge in a way most can grasp. Impressive
That's a great recommendation!
And thank you, that's very kind!
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