Agree on shape being primary factor (second moment of area usually being width x height cubed for vertical bending). Strongly disagree on layup effects being marginal though...
Agree on shape being primary factor (second moment of area usually being width x height cubed for vertical bending).
Strongly disagree on layup effects being marginal though. I know for a fact layup can influence the stiffness to the tune of 5x from the same mould. Granted, what I'm talking about is making things softer, not stiffer, which is a different problem altogether as making a small diameter tube into a rod by filling it in still won't get you to the point that taking a larger diameter tube would stiffness wise, but still. Layup can have an immense factor. It's also not just unidirectional plies that can be used in the layup, which opens up a whole other set of variables.
Great points! I agree, but much of that range won't be usable while still meeting your goals for strength, weight, price, and stiffness. Within the practical...
Great points! I agree, but much of that range won't be usable while still meeting your goals for strength, weight, price, and stiffness. Within the practical limits of bike frame manufacturing, there are many adjustments you can make to the layup. However, you're unlikely to achieve drastic changes in stiffness while meeting those requirements, that's why you end up having to mainly rely on tube section.
Woven plies are interesting but often heavy, and high tech fibers are appealing but typically too expensive to produce a competitively priced frame. It's not that you can't adjust these factors, it’s that you still need to tune them in a way that results in a bike that sells and keeps the business running. Great discussion!
How much does different resin types change the stiffness and feel of carbon?
You don't really see many unique fibre types anymore, I remember having an old road bike with carbon kevlar forks. The rowing boats used to have kevlar in them frequently and have nomex honeycomb decks, everything is just carbon these days.
How much does different resin types change the stiffness and feel of carbon? You don't really see many unique fibre types anymore, I remember having an old...
How much does different resin types change the stiffness and feel of carbon?
You don't really see many unique fibre types anymore, I remember having an old road bike with carbon kevlar forks. The rowing boats used to have kevlar in them frequently and have nomex honeycomb decks, everything is just carbon these days.
That's a good question. I don’t know enough about that part of composites to give you a great answer. In general, a more ductile/compliant resin system probably creates a more damped and/or compliant feel. This allows the fibers to move slightly, with the resin acting more like a spring instead of being brittle and ready to shatter, improving impact strength. However, the trade-off is a reduction in the ultimate strength of the composite, and vice versa. So you can have a more compliant resin, but it leads to a laminate that’s not as strong, so you’d need to use more material to maintain strength, which makes it heavier. But then you’re adding more thickness to the tube wall to make it stronger, so are you really adding compliance, or is it just a heavy carbon frame that still doesn’t flex that much? I don’t know. Different vendors have their own resin systems, but most will end up being similar as they balance strength, durability, cost, and cure time to optimize frame production.
Primoz and you bring up good points. I’m used to being constrained by cost, so I don’t know that much about how to tweak the layup and resin systems to really tune the compliance of a frame. I think the challenge is how to increase compliance with softer resins but also keep strength.
Any composite experts on here who can speak on introducing compliance via composites while also keeping the structure strong?
Unfortunately this won't be happening, as the donor frame is dead haha. Maybe if I can find another donor frame from someone to destroy to test...
Unfortunately this won't be happening, as the donor frame is dead haha. Maybe if I can find another donor frame from someone to destroy to test I'll look at doing it, but my old frame cracked so I won't be able to modify it safely.
I saw this on pink bike this morning, it's obviously a joke/gag bike, but from what little riding we saw, it really does highlight some interesting characteristics of front triangle flex. Worth a watch for sure.
May it RIP in peace 🙏 No worries! Was thinking about how to do this on my bike as well though bike season is now over...
May it RIP in peace 🙏 No worries! Was thinking about how to do this on my bike as well though bike season is now over as I just got my first ski day in (warning: humble brag). I have 17mm aluminum axles for the main pivot and link pivot of my trail bike. I could replace them with a steel bolt that's ~10mm in diameter and 3d print some TPU bushings to take up the space between the parts and that would be a fairly quick way to try this idea on. It'll probably fall apart quickly but should last a few runs. Could just do a few back to backs to see if the idea is worth exploring further. Again, cant ride rn but if anyone else wants to play around with this send it. Happy to held with CAD/2D. It'll be fun for the new year. Excuse the lack of replies recently, I've been working on a future thing for in a few weeks that relates to this.
Hmm Bit late to the party, but I have a bike with pretty big hardware that jumped to mind where I could play with that.
Guess I could press smaller ID bearings. I believe it may be a 5mm step from whatever I'm working with, so I could get 2.5mm thick bushing into a pretty wide section in the frame on either the main pivot, or where the rocker meets the front triangle..which might have an interesting effect and probably not one the shock would appreciate long term.
How much does different resin types change the stiffness and feel of carbon? You don't really see many unique fibre types anymore, I remember having an old...
How much does different resin types change the stiffness and feel of carbon?
You don't really see many unique fibre types anymore, I remember having an old road bike with carbon kevlar forks. The rowing boats used to have kevlar in them frequently and have nomex honeycomb decks, everything is just carbon these days.
That's a good question. I don’t know enough about that part of composites to give you a great answer. In general, a more ductile/compliant resin system...
That's a good question. I don’t know enough about that part of composites to give you a great answer. In general, a more ductile/compliant resin system probably creates a more damped and/or compliant feel. This allows the fibers to move slightly, with the resin acting more like a spring instead of being brittle and ready to shatter, improving impact strength. However, the trade-off is a reduction in the ultimate strength of the composite, and vice versa. So you can have a more compliant resin, but it leads to a laminate that’s not as strong, so you’d need to use more material to maintain strength, which makes it heavier. But then you’re adding more thickness to the tube wall to make it stronger, so are you really adding compliance, or is it just a heavy carbon frame that still doesn’t flex that much? I don’t know. Different vendors have their own resin systems, but most will end up being similar as they balance strength, durability, cost, and cure time to optimize frame production.
Primoz and you bring up good points. I’m used to being constrained by cost, so I don’t know that much about how to tweak the layup and resin systems to really tune the compliance of a frame. I think the challenge is how to increase compliance with softer resins but also keep strength.
Any composite experts on here who can speak on introducing compliance via composites while also keeping the structure strong?
I'm as far from a composite expert as it gets, but I've seen pretty interesting diagrams of how one bike company actually uses different layup per size to adjust for expected average rider weight differences on the different sized bikes. Interestingly, some of those were almost entirely different bikes between sizes.
I don't have much to contribute but I find this discussion really interesting, thanks for that! I can only tell that when I went from a pretty soft rear end on alloy rims onto a very stiff rear end with carbon rims, it opened up lines I couldn't have dreamt of before, and I've been chasing stiffness ever since. Why does that sound wrong? 🤔
I'm as far from a composite expert as it gets, but I've seen pretty interesting diagrams of how one bike company actually uses different layup per...
I'm as far from a composite expert as it gets, but I've seen pretty interesting diagrams of how one bike company actually uses different layup per size to adjust for expected average rider weight differences on the different sized bikes. Interestingly, some of those were almost entirely different bikes between sizes.
I don't have much to contribute but I find this discussion really interesting, thanks for that! I can only tell that when I went from a pretty soft rear end on alloy rims onto a very stiff rear end with carbon rims, it opened up lines I couldn't have dreamt of before, and I've been chasing stiffness ever since. Why does that sound wrong? 🤔
It sounds like you might need to angle your seat down a little. 😉
Agree on shape being primary factor (second moment of area usually being width x height cubed for vertical bending). Strongly disagree on layup effects being marginal though...
Agree on shape being primary factor (second moment of area usually being width x height cubed for vertical bending).
Strongly disagree on layup effects being marginal though. I know for a fact layup can influence the stiffness to the tune of 5x from the same mould. Granted, what I'm talking about is making things softer, not stiffer, which is a different problem altogether as making a small diameter tube into a rod by filling it in still won't get you to the point that taking a larger diameter tube would stiffness wise, but still. Layup can have an immense factor. It's also not just unidirectional plies that can be used in the layup, which opens up a whole other set of variables.
Great points! I agree, but much of that range won't be usable while still meeting your goals for strength, weight, price, and stiffness. Within the practical...
Great points! I agree, but much of that range won't be usable while still meeting your goals for strength, weight, price, and stiffness. Within the practical limits of bike frame manufacturing, there are many adjustments you can make to the layup. However, you're unlikely to achieve drastic changes in stiffness while meeting those requirements, that's why you end up having to mainly rely on tube section.
Woven plies are interesting but often heavy, and high tech fibers are appealing but typically too expensive to produce a competitively priced frame. It's not that you can't adjust these factors, it’s that you still need to tune them in a way that results in a bike that sells and keeps the business running. Great discussion!
How much does different resin types change the stiffness and feel of carbon? You don't really see many unique fibre types anymore, I remember having an old...
How much does different resin types change the stiffness and feel of carbon?
You don't really see many unique fibre types anymore, I remember having an old road bike with carbon kevlar forks. The rowing boats used to have kevlar in them frequently and have nomex honeycomb decks, everything is just carbon these days.
Pretty sure it affects it quite a lot. The strength of the fibre is only along the axis of it. With cloths it's a question of type. Unidirectional is simple as all fibres are aligned to the same axis. With woven cloths it's along two axes. Laying up a part enables you to vary the axis you apply the cloths along, so you get a menagerie of effects.
The point is, fibres are strong along the axis. Off axis it's the resin carrying the load. For a unidirectional cloth it is as strong as fibres (thereabouts) along the axis and as strong as the resin side to side and up and down (perpendicular to the axis).
Peak torque had a good video on the topic. At the end of the day, regardless of choosing steel, aluminium, titanium or carbon, the effective modulus of elasticity for the end material (composite layup in the case of carbon, bulk modulus for metals) and the density of the material will be in a fairly similar ballpark as the layup of the composite to cover all different load directions will add up as Ryan says. A lot of the resin and not much fibres will carry the load, thus lower stiffness vs. raw fibres. So there is no silver bullet weight wise except berilium... Stiffness (as per the topic) is a different discussion though.
As for my previous comments, a lot can be achieved, but price might vary, yes. What I was talking about is likely not something that can be achieved with currently expected, offshore manufacturing capabilities at currently expected volumes and/or prices.
Hmm Bit late to the party, but I have a bike with pretty big hardware that jumped to mind where I could play with that.Guess I...
Hmm Bit late to the party, but I have a bike with pretty big hardware that jumped to mind where I could play with that.
Guess I could press smaller ID bearings. I believe it may be a 5mm step from whatever I'm working with, so I could get 2.5mm thick bushing into a pretty wide section in the frame on either the main pivot, or where the rocker meets the front triangle..which might have an interesting effect and probably not one the shock would appreciate long term.
I just got my 3D printer running with TPU and I could print some bushings to try. If you want, let me know what the basic dimensions of the bushings would need to be and I can help to design and print them and we can see what happens! Feel free to DM me too and we can chat about the design.
How much does different resin types change the stiffness and feel of carbon?
You don't really see many unique fibre types anymore, I remember having an old road bike with carbon kevlar forks. The rowing boats used to have kevlar in them frequently and have nomex honeycomb decks, everything is just carbon these days.
That's a good question. I don’t know enough about that part of composites to give you a great answer. In general, a more ductile/compliant resin system probably creates a more damped and/or compliant feel. This allows the fibers to move slightly, with the resin acting more like a spring instead of being brittle and ready to shatter, improving impact strength. However, the trade-off is a reduction in the ultimate strength of the composite, and vice versa. So you can have a more compliant resin, but it leads to a laminate that’s not as strong, so you’d need to use more material to maintain strength, which makes it heavier. But then you’re adding more thickness to the tube wall to make it stronger, so are you really adding compliance, or is it just a heavy carbon frame that still doesn’t flex that much? I don’t know. Different vendors have their own resin systems, but most will end up being similar as they balance strength, durability, cost, and cure time to optimize frame production.
Primoz and you bring up good points. I’m used to being constrained by cost, so I don’t know that much about how to tweak the layup and resin systems to really tune the compliance of a frame. I think the challenge is how to increase compliance with softer resins but also keep strength.
Any composite experts on here who can speak on introducing compliance via composites while also keeping the structure strong?
Hmm Bit late to the party, but I have a bike with pretty big hardware that jumped to mind where I could play with that.
Guess I could press smaller ID bearings. I believe it may be a 5mm step from whatever I'm working with, so I could get 2.5mm thick bushing into a pretty wide section in the frame on either the main pivot, or where the rocker meets the front triangle..which might have an interesting effect and probably not one the shock would appreciate long term.
I'm as far from a composite expert as it gets, but I've seen pretty interesting diagrams of how one bike company actually uses different layup per size to adjust for expected average rider weight differences on the different sized bikes. Interestingly, some of those were almost entirely different bikes between sizes.
I don't have much to contribute but I find this discussion really interesting, thanks for that! I can only tell that when I went from a pretty soft rear end on alloy rims onto a very stiff rear end with carbon rims, it opened up lines I couldn't have dreamt of before, and I've been chasing stiffness ever since. Why does that sound wrong? 🤔
It sounds like you might need to angle your seat down a little. 😉
Pretty sure it affects it quite a lot. The strength of the fibre is only along the axis of it. With cloths it's a question of type. Unidirectional is simple as all fibres are aligned to the same axis. With woven cloths it's along two axes. Laying up a part enables you to vary the axis you apply the cloths along, so you get a menagerie of effects.
The point is, fibres are strong along the axis. Off axis it's the resin carrying the load. For a unidirectional cloth it is as strong as fibres (thereabouts) along the axis and as strong as the resin side to side and up and down (perpendicular to the axis).
Peak torque had a good video on the topic. At the end of the day, regardless of choosing steel, aluminium, titanium or carbon, the effective modulus of elasticity for the end material (composite layup in the case of carbon, bulk modulus for metals) and the density of the material will be in a fairly similar ballpark as the layup of the composite to cover all different load directions will add up as Ryan says. A lot of the resin and not much fibres will carry the load, thus lower stiffness vs. raw fibres. So there is no silver bullet weight wise except berilium... Stiffness (as per the topic) is a different discussion though.
As for my previous comments, a lot can be achieved, but price might vary, yes. What I was talking about is likely not something that can be achieved with currently expected, offshore manufacturing capabilities at currently expected volumes and/or prices.
I just got my 3D printer running with TPU and I could print some bushings to try. If you want, let me know what the basic dimensions of the bushings would need to be and I can help to design and print them and we can see what happens! Feel free to DM me too and we can chat about the design.
Some cool seat stay bridge options from Atherton Gearbox proto
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