Hey, I’m Ryan Burney. I’ve spent eight years as an engineer for full-suspension bikes, working on some fun projects, like developing the flex Horst link for the Cannondale Scalpel and being lead engineer for the latest GT Fury downhill bike. With over a decade of downhill racing under my belt (even made it to one World Cup—though I didn’t qualify so I stuck to engineering), I've had the pleasure of racing alongside the Vital crew, like Jason, Tanner, and Dak. Below is a photo of me, being slower than Dak. These days, I’m focused on my own projects, but I love the Vital community and wanted to jump into the good conversations happening here. Today, we’re diving into frame compliance and what it means for a bike's handling.
Please note that the following insights and conclusions are my own thoughts, observations, and opinions based on my experience riding bikes. Definitely could be wrong 😊.
What is Compliance?
So, what is compliance? It's essentially a fancier way of saying "reducing stiffness." Stiffness is how much something bends when you apply force to it. For a long time, the goal was to make bikes as stiff as possible. But after enough riders rattled their teeth out, we learned that it’s all about balance. Stiffness has its pros and cons, and the same goes for compliance.
Lately, many top downhill riders have been tuning their bikes to increase compliance. Why? To smooth out their ride. When you’re flying through rough terrain at speed, your ability to go faster can come down to how well you can see. If your eyeballs are bouncing around in your head like little mass dampers, you’re going to be forced to back down. Plus, your hands hurt, your body gets fatigued, and you generally just get beaten up.
Focusing on stiffness on bikes isn’t new; it’s been measured for a long time, especially on road bikes. Road bikes have been around long enough to truly refine their designs. Their simpler chassis allows for easier isolation of ride characteristics from design changes. Mountain bikes have only recently reached a point where most are considered really good. Thanks to refined suspension design and geometry, we can now chip away at the finer details like stiffness. It’s not that mountain bike companies weren’t aware of stiffness in the past, but they had larger issues to deal with, like frames rattling apart and bolts breaking. There was a lot to figure out before they could start making the rider more comfortable.
Stiffness and Its Impact
Stiffness matters. Certain stiffness traits affect control, efficiency, and comfort. There are standard tests for bottom bracket and head tube stiffness, which measure how much a frame flexes when forces are applied. Bottom bracket stiffness measurements show you how much your bottom bracket wags to a side when pedaling and gives you insight into the perceived pedal efficiency of a frame (that’s a whole other conversation—please feel free to ask about it in the comments). Head tube stiffness tells you how the bike may handle when given steering inputs and measures how much a frame twists given a certain force.
So, what makes for good stiffness? You need enough stiffness in key areas to ensure your bike performs its essential functions—like steering and pedaling—without making it so stiff that you’re lugging around excess frame material. Personally, I prefer bikes that go where I point them and don’t feel like a noodle when I’m mashing the pedals. I prefer an al dente frame stiffness. Where you have your stiffness on the frame makes a big difference to handling and adding compliance without a strategy can come to bite you.
The Importance of a Stiff Front Triangle
Let’s dig into why we want the front triangle to be stiff. The front triangle's stiffness is essential for maintaining steering precision. If the front triangle flexes too much, it can "wind up" under load. It can happen during hard braking to where your fork is wobbling fore and aft via the front triangle or high G berms where the fork can point over the one side of the bike. This twist in the front triangle affects the position of the front wheel, which directly impacts how the bike steers and your timing of front wheel placement. Unpredictability in the front end is something you want to avoid—when you’re going into a corner or tackling a rough section, you need to know that the front wheel is exactly where you expect it to be. Otherwise, you’ll lose trust in the bike and back down.
Introducing Compliance Through the Rear Triangle
This is where the rear triangle comes into play. Since we want a stiff front triangle for precise handling, we can introduce compliance through the rear triangle to improve comfort and control. The rear triangle can flex in different ways to help the rear wheel move out of the way of impacts and obstacles without sacrificing too much control.
We’re talking about two directions of compliance from the rear triangle.
Roll: This is when the rear wheel rotates side to side about the chainstays (viewed from behind) as the wheel encounters angled obstacles. If the rear triangle is too stiff, these impacts can knock the wheel off line. Flex in this direction allows the wheel to track the ground better by reducing that "side-knock-off-line-effect" (fun term, right?), which improves grip and comfort through rough terrain. Most importantly, when the rear triangle and wheel roll side to side, the rear wheel stays straight, without changing the direction it's tracking on the ground.
Wag: This occurs when the rear triangle wags side to side, like a tail, when viewed from the top. This compliance also helps prevent the wheel from being knocked off line, especially on chunky, straight sections. However, too much wag can introduce a form of two-wheel steering in high-load corners. The rear wheel starts to steer independently of the front, and this happens more or less depending on how hard you load the bike. It can feel unpredictable, but hopefully, the wheel changes direction as expected when you come into that tight berm hotter than planned during your race run 🤞.
It’s crucial to find the right balance between roll and wag, as each affects the bike differently. Personal opinion incoming: Ideally, the rear triangle flexes via roll enough to allow the rear wheel to deflect impacts and avoids as much wag as possible, mitigating unpredictable steering. Too much flex in either roll or wag can leave you with you guessing where the rear wheel is as you lose your feeling of the ground through your feet. It’s smooth as heck but if you don’t know when your rear tire is on or off of certain obstacles you’re just guessing and eventually that will bite you and you’re going to have a bad time. Let’s look at a few bikes to help illustrate what we are talking about.
Example A: Amaury Pierron's Commencal Supreme
Amaury’s bike showcases both types of compliance—rear wheel roll and wag. The tiny chainstays flex significantly, effectively deflecting impacts. However, because the seat stay is stiffer and angled upward, the rear triangle allows both roll and wag. Imagine the wheel twisting about the seat stays when the rear triangle is loaded in a berm. This twisting both rolls and wags the wheel simultaneously when the frame allows the wheel to deflect from rocks. The roll is appreciated but the added wag introduces a degree of two-wheel steering, which complicates things. As discussed earlier, this wag makes the bike feel less consistent because the amount of two-wheel steering flex varies depending on how hard you hit a berm or corner. You’re left guessing how much the rear end will flex, which can lead to unpredictability, especially at high speeds. While Amaury’s bike performs well in rough terrain (and there’s no arguing its overall performance), this combination of roll and wag presents this challenge in high-G corners.
That said, these observations are hindsight reflections based on seeing where other teams are finding frame compliance. Amaury’s setup may not have as much of a compromise as I think it does. Who knows—it may be the next sliced bread. The chainstay is an okay place to introduce compliance just proceed with caution. I think there are better areas to introduce compliance with fewer compromises. Let’s take a look at another frame layout with a completely different approach to stiffness and compliance.
Example B: Loic Bruni’s Prototype Specialized
Let’s look at Loic’s bike. His setup takes a different approach, featuring very large chainstays and smaller seat stays that provide rear wheel roll without much wag. This design allows the rear wheel to still move out of the way and deflect impacts while minimizing wag during cornering. As a result, Loic benefits from rear triangle compliance—like increased comfort and traction over rough terrain—without sacrificing handling precision in corners, as there isn’t much wag to contend with. The race team also swaps out the seat stay linkage between bridged and bridgeless links to further tune compliance in this same direction. His bike should feel very consistent, enabling him to push harder through technical sections without worrying about unpredictable two-wheel steering. Additionally, the high bottom bracket stiffness (thanks to those chonky chainstays) prevents significant lateral flex while pedaling, ensuring high bottom bracket stiffness which equates to a part of the equation of high perceived pedal efficiency. This is excellent for a racer’s mental game.
Conclusion
In the end, achieving the right frame compliance is all about strategically balancing stiffness and flexibility in the areas that matter most. You want a stiff front triangle to ensure control and prevent twisting under big loads, while introducing carefully tuned compliance in the rear triangle enhances comfort and traction without sacrificing handling.
These examples highlight the pros and cons of different designs, though every frame layout brings its own unique advantages. Some frames allow for greater compliance tunability than others, and bike technology has made great strides in working towards the sweet spot between stiffness and compliance. Ultimately, the ideal mix will depend on the specific problems a design seeks to solve, as well as each rider’s strengths and preferences.
While compliance can smooth out your ride and keep you from being slowed down by the terrain, having too much in the wrong places can reduce control, leading to inconsistency and unpredictability. As bike designs keep pushing forward, achieving this balance will be what turns a good bike into a great one.
I'm stoked to hear what others are enjoying/disliking when it comes to frame stiffness and compliance. And I'm happy to answer any questions about the topic!
What kind of compliance do you think Dak's bike has?
Mmm, al dente tubes for crab links
Hey Ryan, appreciate this Post! I had a chance to ride the new fury for a few days and I think you and Luis did a great job on the new version compared to the 2023 model.
It’s interesting to hear your philosophy on stiffness and Compliance because I felt exactly what you mentioned above on the fury. In my opinion, I think the front end was a little too rigid for me, at my speed and riding level. The rear end to me was much more to my liking of how I like a bike to ride and feel.
Do you think we could ever get to a place in Production where there is a consumer spec of Compliance and then a race team version or could accompany ever offer a compliance version and a stiff version? There’s so many things that come into play besides rider skill level, weight but even trail pitch and dirt texture. For example, riding in the southeast versus Southern California is much different as far as grip from dirt.
Also I was wondering what you think about the link and rear and modifications that Danny Hart’s mechanic did this year on the World Cup.
Is there anything that we could do to the front end to reduce some rigidity that is felt through the hands and feet?
I think various links used to connect the rear axle to the main frame need to be accounted for. Horst links, short link 4 bar and direct single pivot designs all have different loadings at the joint. Is it common practice to consider them rigid but articulating joints?
Great questions, Carlino! Luis is the man and a pleasure to work with, his kinematic knowledge is the best. Bikes like the Commencal and Ari, with removable seat stay bridges to tune stiffness, show where the industry could head. It’s a great way to dial in feel based on rider preference and terrain. Danny’s mods are an example of getting that little bit extra of compliance out of your frame for a lighter rider. Lighter riders often benefit from reduced stiffness while larger riders need stiffer frames to maintain the same feel. Though I don't know everything about the exact reasons for Danny's mods as I am not at GT anymore so that's a guess. Road bikes address this with size-specific tube scaling, but mountain bikes often reuse rear triangles across sizes, aiming for a middle ground. Removable bridges could be a great step toward size-specific compliance tuning though you run into the problem of adding yet another thing to add to the setup list on your bike which may not make sense for all riders but great for a race bike and us bike nerds.
Regarding front triangle stiffness and hand fatigue, it usually has minimal impact on hand feel unless there’s extreme flex. If the front triangle or fork flexes too much, the front axle and bars move fore/aft, creating that “ripped out of your hands” sensation. The Fury avoids this with an appropriately stiff front triangle... I'm super biased though 😊, but I understand how riders want to keep their hands from fatiguing, I'm personally obsessed with that (soft hands). Hand fatigue will mostly be address through the below components:
Grips: Smaller grips so your hands don't have to work as hard to stay on the bar.
Bars: Compliance bars like OneUp help with harsh chatter. I see you have pretty beefy bars on your bike, that would be where I'd start.
Fork Tuning: Reduce low speed compression to keep the front end from stuttering. In braking bumps low speed can really work against you.
Tire Pressure: Lower pressure helps, go as low as you can without rolling tires.
Wheels: Vertically compliant wheels, like your Crank Brothers, are great.
Maybe the mass dampers will help??
For foot feedback, consider more laterally compliant cranks like the carbon Sram cranks or an O-Chain or E13 Sidekick hub for reducing pedal feedback even more, though the idler already helps. Glad you’re enjoying the whip!
Good points! The more pivots/joints you add to a bike, the less stiff it becomes. For example, a hardtail will always be stiffer and lighter than a short link 4 bar bike. Adding pivots reduces structural efficiency, meaning you have to add more material (and weight) to maintain stiffness. More pivots = less stiffness and more weight. But suspension is pretty cool to have... so the key is finding the right balance with as few pivots as possible to make the bike perform well. Did that answer your question?
Let's not use a hardtail as an example, we're working with full suspension bikes 😉
Haha, fair! I think going to extremes in examples helps illustrate points, so you'll see me slipping into that mode a lot so my apologies in advance. Let's compare a single pivot to a short link 4 bar and just look at the chain stay and its stiffness:
A typical single pivot has a set of main pivot bearings between the bottom bracket and the rear axle. A short link 4-bar, on the other hand, has two sets of bearings at the link near the bottom bracket. Having two sets of bearings between the bottom bracket and the rear axle will almost always be less structurally efficient than one when connecting the bottom bracket to the rear axle. Kinda fun to boil it down and think about it like that, right?
That's a good point about short link 4 bar. Does adding the corresponding upper link (and it's additional bearings) help or hinder the desired compliance in flex or roll? To bring you back to Dak's bike
Imagine a bike with just a chain stay, like a dirt bike with no seat stay. This design mainly allows roll. Now add a seat stay about the same size as the chain stay, and you should get way more wag and way less roll. How much? It depends, but Dak’s bike has smaller seat stays and larger chain stays, so it’s a blend of roll and wag but likely has more roll, similar to the Specialized, just not as much. Dak should also be able to tune the rear triangle roll with this plate pictured below. We’ll have to ask him what he feels!
As for the upper link and its influence on rear triangle stiffness, think of it like the short link on the chain stay we talked about earlier in this discussion. If your goal is to reduce stiffness in an area then adding a bearing helps to do that and so the link conveniently is doing that.
to expand on rhodefab's original question a bit, I'm curious how stiffness is analyzed for geometrically complex systems like full suspension bikes. how do you find yourself estimating total stiffness in a given direction (like roll or wag) most often? I can see a springs-in-series approach being useful for quick iterations, but I'd assume that FEA tools are necessary at some point to get more accurate values, assuming that you aren't yet ready to test it on a load rig.
also, awesome writeup in your initial post. it really helped piece together some of the intuitions I had about what DH teams are doing on this front in a really cohesive way.
For sure, I agree with you. I love this type of content.
I am running OneUp Aluminum bar, Ochain. I have mass dampers on my current frame, but I didn't run them on Fury.
To onto PacoJo question, I have been using SynBike data acquisition to measure frame movements with the 6axis IMU's. I've only had it on 2 frames now, but would interesting to hear how the baseline of compliance is chosen, FEA or ride tested on dirt?
Photos here of Danny's modified rear end from PB for people who haven't seen it.
First off, thank you! And that’s a solid question. You can FEA full frames and estimate deflections, but you’re making a lot of assumptions, and they start to stack on each other, so things can stray from reality quickly. And speed to reality is crucial. Using FEA is useful but only for very basic analysis and often you can guess what's going to happen: I made the chain stay bigger, it got stiffer. FEA is useful for validating a scenario where I wanted it exactly X amount stiffer and then you verify in the test lab.
I’ve always wondered if full suspension bikes should be dug into as far as you’re mentioning, but you always run out of time, and that’s normal and that’s ok. I took that same curiosity into my other job, where I spent the last year working as an engineer on a rally car team and got to see much more refined (cars are pretty refined) and complex systems go from concept to reality. My observation is that those who make a good guess based on previous observations and work to solve the highest priority problems, then get that thing under racers the fastest, learn the most the fastest. You’ll make a faster bike faster and with less resources than those who spend all their time refining models. I think that’s where bikes and most race cars are now (F1 and other super high budget projects are different). Make it, test it, learn why/where you were wrong and right, and do it again. You also get to learn things you didn’t expect or assume would happen, which is always the best part.
Having a highly refined model of stiffness on the computer is always the dream, but again, you can learn so much faster and cheaper (because less time invested) by making the thing. I bet as the time investment to make a good computer model goes down, we’ll certainly see more of it!
One thing you can try is doing a bit of a suspension setup reset. Open up all the compression, set it up soft, and then start adding compression and spring rate until it bothers you or you get thrown around too much. That may be the balance you need to hit. Everyone wants to run all the compression clicks and keep their bike firm cuz the local cool kids do it, but if you can’t hold on or get fatigued immediately, none of it matters. A tired rider is a slow rider, no matter how dialed their suspension setup is.
Maybe try prioritizing comfort more in your setup and see how it goes. Its also a fun experiment. You might have to deal with a bike that feels less peppy, but it could actually be faster and higher-performing than a "fast" setup that makes you tired. For example, since I don’t ride bike parks as much as I used to, my hands aren’t as strong, so I have to run the front softer. That means I also have to run the rear softer to maintain balance, but honestly, things are so much smoother now. I think I’m actually going faster even though it doesn't "feel" as fast, and I’m notably less fatigued when charging. I wish I had run my suspension softer when I was racing. By the time you get to the race run, you’re already tired from practicing all weekend… and again, a tired rider is a slow rider!
Yeah definitely I run a more comfort setting than performance.
I guess part of our compliance comes from frame material as well. I personally I have never rode a carbon front end that had the same comfort and vibration damping of a steel, aluminum or print/bonded frame.
Everyone is different, so I understand it’s tough to just make one frame that racers and consumers are all going to thrive on.
Have you seen the fore/aft compliance on this bike Sam P was riding? lol
I think that we’ll likely start seeing frame layouts on certain bikes, like e-bikes, begin to converge. Since designing a good, longer-travel e-bike is mostly a packaging exercise (you gotta fit all the things and it has to do all the stuff which means you can only layout your frame and tubes in a few ways) many frames will end up looking similar. That will create an excellent opportunity for differences in materials and tunable frame compliance to stand out, highlighting how simple design changes can affect the way a bike feels -like on road bikes. You're right, right now everything is so all over the place layout-wise that it can be hard to pinpoint why one frame performs better than another. We see that in reviews all the time. Should be a fun upcoming 5 years of learning from the e bikes. aaaaannnd I have not seen that video haha. Just watched that video you shared from SP, what's funny is that spring bike gives some great visuals on what we are talking about. Check out what happens when he goes into berms and how his fork/hands bounce back and forth since it flexes so much. On a normal bike this won't happen as much but you can see some of this in high load scenarios like berms if your front triangle is a noodle. Here is the video carlinojoevideo is talking about: SP Spring Bike.
Hi Ryan! Awesome post, thank you very much!
What are your thougths about different frame materials in regards of stiffnes and compliance? Makes sense to you that carbon and alloy versions of a frame share the same design/layout?
What do you think about steel full suspension bikes?
Glad you like it! This is a great question. A lot of people think carbon is always too stiff and aluminum can mute trail chatter but we also often hear people say the exact opposite. The truth is you can make an overly stiff or overly compliant bike out of either material. It all mostly comes down to tube size and wall thickness. Oh and frame lay out.
If you make a frame with teeny tiny carbon tubes it will flex a lot, and huge tubes will make it overly stiff. Same goes for aluminum. The key difference is that carbon’s material properties allow you to create a tube that can be stronger and lighter than aluminum so you can make a lighter bike. Plus, carbon gives you the advantage of tuning stiffness and compliance through fiber orientation in the layup, letting you control how a tube flexes and twists which is cool. With aluminum you are limited to using only tube shape and wall thickness to tune strength and compliance = not as fun.
As for how they handle flex, here is where it gets interesting. Carbon doesn’t dissipate much energy when it bends so it can spring back on you more than you may like, almost like a shock with no rebound damping. Some might find that a bit hard to tame. Aluminum, on the other hand, has a grain structure that introduces slight internal friction when it flexes and returns to shape. This is called hysteresis and it helps dampen the spring back, making the flex feel more controlled. Note this is very slight but people seem to swear they can feel it 🤷. But your bike is heavier, so is that trade off worth it? Also, if your frame isn’t winding up much then it is not springing back much either so you may not need aluminum to dampen the ride. It’s a subtle but cool advantage in certain designs. Note: I am not a materials expert so I may be off here. These are from my own research and riding observations but I think its mostly right. Please correct me if anyone here knows more.
As for steel, it’s a similar story to aluminum but it’s heavier. For a certain tube size with a certain strength, carbon will be the lightest, aluminum will be second, and steel will be the heaviest. Steel bikes are often called comfy because they flex more, but that’s not because steel itself is super flexy—it’s because you need smaller tubes with thinner walls to keep the weight down to a bike weight you actually want to ride, and that ends up giving you those traits. Steel is real though. It’s easy to work with, you can even build a bike at home, and I like that stuff.
At the end of the day, it’s a lot like the 27.5 vs 29er debates. Pick a material you like and be a d*ck about it because it doesn't matter that much and its fun to debate. They can all make great or terrible bikes. Have fun on whatever material makes you happiest 😎
And to finally answer your question of if carbon and aluminum should share the same frame layout: yeah that's no problem, you just may need to make your aluminum tubes smaller to keep weight down.
Been experimenting with larger grips as opposed to smaller ones and notice they’re easier to grip as OD increases. I have smaller than average hands so I have doubts we’re really addressing this problem correctly.
The extra padding can help and for some people it's the solution. Personally, I find the smaller grip to be easier to hold onto like a small vs large diameter pull up bar. Everyone is different so if you've found that to work well, rock it!
Any questions on compliance?
Is there a benchmark frame that you have found to be the ideal mix of compliance and ride feel?
Great post, Ryan. Made me think about my bike, not to quantify its goodness but just to appreciate it.
Seems like the ovalized chainstays would reduce wag but increase roll. Interesting!
I have a question about the stiffness and compliance on the bike as a whole system and is there anyone looking at this? For example: you talk about the tradeoffs in the RT but if paired with a rear certain wheel does that is overly stiff or compliant are you negating the effects in some regard. Or on the other end, an overly stiff front paired with a inverted fork might be better than a traditional fork. I guess to simplify it, if you were to design a bike just for your preferences would the stiffness of your preferred components play into how you tune your frame?
Flex is great... until it isn't. It seems to be this subtle thing that is largely ignored or not reacted to, until a big flex happens where the bike seems to "disappear" for moment, providing that "vague" feeling and possibly shaking confidence.
Flex also seems to be something that is both structurally and input driven. So a minor flex on a mellow event can turn into a larger flex in a high load event.
A couple of questions:
- when talking roll and wag flex, how many millimeters: is a little, is a lot
- For a consumer's bike, how do you tune structural flex for the wide range of possible inputs different riders have (weight, skill, etc)
- How to interpret when flex is bad flex? (Just because it feels spooky perhaps does not mean it's bad for grip?)
Thanks for sharing your knowledge with us.
Do you guys measure flex in a lab setting when designing bikes?
Or perhaps more interestingly do batch testing for flexiness during production. I know from first hand experience due to frame alignment and normal manufacturing variations some bikes wobble (not flexing I know) quite a bit when shaken from the BB or read wheel due to how the pivots and bearings all seat together and some are absolutely rock solid.
I know manufacturing tolerances is a different question but as designers do you consider this when designing compliance into a frame?
Can we get a side thread on what went into designing the horst flex stays at Cannondale? I have geeked out hard over anything I could find online on those flex stays. Some site had images of steel plate bolted into aluminum stays.
This spring I built a frame that ditched two pivot point and relied on the seatsays to flex for both of them. Originally I envisioned it as flex horst but started running short on my build timeline and thew caution to the wind a decided to torture test the seatstays on a 160mm enduro frame. .
I’ve definitely ridden bikes that have rattled my teeth out and bikes that have been too flexy. I’ve really enjoyed the Stumpy Evo’s ride quality, and of course, I like how the Fury rides (but I’m biased). There was focus on being strategic with compliance on the Fury, and I think it shows in how it rides. I can’t say I’ve personally found the best-balanced bike, as the focus on it hasn’t been top of mind when riding bikes in the past since the industry was focused on other priorities. As of late, I’ve not been test riding a lot too, so I’m falling a little behind on tbh. I think we will see this type of stuff talked about in reviews this upcoming year, so we will learn more about which bikes have a really good mix of compliance and ride feel then. So I can't say I know the bike that has the best mix of compliance and ride feel.
Thank you! That Reeb is super cool. I would run that as a daily. That extra width definitely doesn't hurt!
That's something that should be considered, but many companies probably don’t do much about it otherwise they would talk about it more. Components have gone through their own renaissance in terms of compliance, like bars and wheels, but you don’t often see them designed as a complete system. For the most part, it’s fine, so long as you don't have a component holding your bike back too much, but if you really wanted to fine-tune a bike, designing all the components to work together would be ideal. Most frame companies don’t make all the parts on the bike, so it’s hard to tackle this.
Maybe someday we’ll see a company that has in-house wheels and frames lean into this. It would be cool. You’re absolutely right with your examples, a stiff frame paired with a noodle wheel probably wouldn’t be ideal, or vice versa... I'm not sure. If you were to design a bike just to your preferences, the stiffness of your preferred components would definitely play a role.
One thing a race team can be strategic about is ensuring they have the components they like on the bike before iterating the frame. It would suck to develop a frame and then your wheel sponsor changes dramatically. Designing a frame around a wheelset that’s too stiff or too soft may not work well for the end consumer who might use a different set of wheels. Road bikes with their integrated cockpits are probably considering this stuff more than mountain bikes as they've been in the refinement stage longer. Great points and exactly the kind of ideas this article is meant to stir up.
If you were to sum up this article in one sentence, you’re right, it would be Flex is great until it’s not haha. You are correct, since bike frames (and everything) is just a big spring, the harder you push the more it bends, make sure to design it so when it is pushed hard it does not bend more than you want. The amount of flex depends and I do not know honestly. I could make a test machine that measures a frame as a reference in the direction I want to look at and then refer back to it as I change the design though and at least work in the right direction. The amount will be more for a heavy big rider in a corner and less for a small rider going the same speed in that same corner so it is hard to give a real number. A way you can define those numbers is to find out what too much flex is then design something to avoid that much flex. For a consumer's bike, that is ag question right now for many product management mtb teams I bet. Since we finally just got geo dialed, the next hot topic and thing that could notably improve your ride experience may be compliance (though I should mention working on compliance will not be the silver bullet that makes your bike 1000% better, just a little bit) How do you implement that for everyone? You probably cannot do it for everyone but you could accommodate for most people with things like changing tube sizes on the front triangle (fairly practical) and on the rear triangle (less practical as all sizes often share the rear triangle to make the bike affordable). I think the removable tunable links and bridges will help with this but it will be fun to see if anything else comes out of the woodwork! Bad flex is the kind of flex that scares the sh*t out of you where it be almost crashing or causing you to crash. Or, you can't tell what's happening beneath you so every now and then when you crash, its hard to determine why, and so its hard to avoid the next crash in a similar scenario. Once these happen, you probably can no longer trust the bike (I cannot) and you will now not ride it as aggressive as needed to win "safely". Hope that answered all of your questions. Happy to have these fun conversations!
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