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ThomDawley Added a reply to The flex stay discussion thread
6/26/2025 9:04am Hey @seanfisseli there are already enough negative misconceptions surrounding flex stay suspension systems and (as a guy making them) I’d love to help put those misconceptions to bed. But it’s pretty difficult to show you something that isn’t happening. Can you help me out? The vid you posted shows a lightweight XC bike hucked to flat, I think I see...
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Primoz Liked a reply to forum topic The flex stay discussion thread
6/25/2025 11:12pm
Add a pivot. It will be EXACTLY the same.
This forum topic has 150 replies.
Primoz Liked a reply to forum topic The flex stay discussion thread
6/22/2025 12:52pm
Buckling is when the structure becomes instable and fails under load. So no, what you're looking at is not buckling. But buckling resistance is also a science on it's own. I think I get it now (kind of got it before you wrote it out in your previous post). Story time. Take your flex stay bike. Remove the aircan from the shock to be left with what is a damper only. Cycle it through the travel. Let's say it's an XC bike with 100 mm of travel at 45 mm shock stroke. When the shock reaches the 45 mm of...
This forum topic has 150 replies.
dolface Liked a reply to forum topic The flex stay discussion thread
6/22/2025 11:36am
Here's an article by Rob on the topic: https://escapecollective.com/the-whys-of-bike-tech-the-myth-of-vertical… " My conclusion from reviewing these connected systems is that the best way to add this mystical “vertical compliance” is by adding air volume and lowering pressure at the tire, and with careful selection of the seatpost."
This forum topic has 150 replies.
ThomDawley Added a reply to The flex stay discussion thread
6/22/2025 11:35am Hey folks, been reading here. Just wanted to chime in to say I fully agree that vertical compliance is a myth. At best it’s misunderstood. The idea that a frame is deflecting enough to provide any meaningful results when the tyre has over 2” of travel is daft. But marketing exists and here we are. I do believe certain materials...
earleb Liked a reply to forum topic The flex stay discussion thread
6/22/2025 11:15am
Vertical compliance in a hardtail road or MTB is a myth. It doesn't happen on any real world measurable amount. On a hardtail and flex felt is coming from the seatpost. Here is some analysis for you to dig into. https://www.albatrossbikes.com/projectgallery/2020/12/17/dropped-stay-c… There is more out there if you go looking. Rob English frame builder and engineer has discussed it on several podcasts. He builds with very thin seatstays and people are always asking him about the vertica compliance. Hardtails and road bikes have lateral compliance and the bracing between chainstays and seatstays are a big driver here. I watched the...
This forum topic has 150 replies.
CascadeComponents Liked a reply to forum topic The flex stay discussion thread
6/22/2025 6:49am
The aluminum stumpy was more similar to the evo. I’d go as far as to say the flex stay stumpjumper had more similarities to the epic than the rest of the stumpjumper line. I think one of the things I’ve been trying to convey is that design choices for a bike on a whole drives the sensation you are talking about way more than anything else. They made a bike that was much more pedal oriented and it behaved as such while happening to have flex stays.
This forum topic has 150 replies.
Glacial Pace Liked a reply to forum topic The flex stay discussion thread
6/22/2025 6:46am
The flex stay will offer an extremely small amount of undamped spring I think, but so does the front triangle, and the rear triangle of bikes that don't have flex stays, it's just so small that is not really something that you would generally say would introduce significant changes to the feeling of the suspension. I think what is happening is that generally flex stays are used to reduce weight, but weight reduction won't just be applied to the stay but the rest in the bike as well, and the wheels etc. plus they are shorter travel bikes so the...
This forum topic has 150 replies.
CascadeComponents Liked a reply to forum topic The flex stay discussion thread
6/22/2025 6:45am
This will be my last attempt at explaining why rebound damping at the shock will control the flex stay. If you take the blur rear triangle and attach the upper pivot to the lower pivot with a rigid member, you are forming a triangle and locking out the flex stay. If the shock were to be locked at any given position, it’s effectively doing the same thing. As such, for the flex stay to move the shock just move and therefore the damping at the shock is controlling rebound of the flex stay.
This forum topic has 150 replies.
earleb Liked a reply to forum topic The flex stay discussion thread
6/22/2025 6:42am
Also to add for the seatstay in a flex design to buckle something else has to also give. The chainstays in tension would need to stretch/bend or something at the other end needs to move (rocker,top tube rocker mount, shock mount, top tube flex). No one thing can move in isolation without something else in the chain moving.
This forum topic has 150 replies.
earleb Liked a reply to forum topic The flex stay discussion thread
6/22/2025 6:42am
Rigid bike flexing vertically doesn't happen. It's a triangular structure, in order for the seat stay to flex you would need either the seat tube or the chainstays to also flex and force needed to bend those is huge.
This forum topic has 150 replies.
earleb Liked a reply to forum topic The flex stay discussion thread
6/22/2025 6:33am
The seatstay is flexing forward of the riser at the dropout. This is where a pivot bearing would be if it wasn't a flex design. The one thing to point out is that the seatstay doesn't likely have this much visual deformation when it flexes. The CAD simulation will have a deformation scale, this exaggerates the visual of how much something is flexing. Something can look like it's flexed like a pasta noodle in CAD but it's only moving a few mm.
This forum topic has 150 replies.
earleb Liked a reply to forum topic The flex stay discussion thread
6/22/2025 6:31am
The Busby patent for dorks like me that were curious about it. https://patents.google.com/patent/US6092823A/en
This forum topic has 150 replies.
earleb Liked a reply to forum topic The flex stay discussion thread
6/22/2025 6:30am
Every flex design that's ever made it to market is just replacing a bearing joint that has a very very low angle of rotation with a flexure. The pivot point will have an angle of rotation in the 1-5 degrees range. The rest of the kinematics play a much bigger role than the bearing that has been replaced ie Horst / Faux bar / VPP will determine the ride characteristics and not the flex.
This forum topic has 150 replies.
Digit Bikes Liked a reply to forum topic The flex stay discussion thread
6/22/2025 6:29am
I've been an engineer on a few flex stay bikes and have seen the "negative spring" narrative evolve. Let's say the distance between the pivots on a seat/chainstay part changes 4mm. It's smart then to design the part at the 2mm position to equalize (and thus reduce) the strain at each extreme. From there it's a short walk to a marketing story where "the rear triangle is in it's neutral position at sag with negative spring effect in extension and positive in compression. It's not untrue, but in reality it's inconsequential compared to the force from the spring in shock...
This forum topic has 150 replies.
earleb Liked a reply to forum topic The flex stay discussion thread
6/22/2025 6:23am
You need to get past that it's somehow undamped. The stays can't move without the shock moving. Full stop. If the stay moves the shock moves so there is damping. I have build a steel fs with 160mm travel that replaces not just one but two pivots with flex in the seatstays. It sit's neutral at 40% travel and takes just light finger pressure to get it to move through the travel. The additional spring force is NOTHING compared to the shock spring. I have some video of the rear end flexing from last year when I first built it...
This forum topic has 150 replies.
ThomDawley Added a comment about bike check Dawley T16
6/10/2025 1:43pm
Thanks for the kind words!
This bike check has 12 comments.
edwardyoon Liked a comment about bike check Dawley T16
6/10/2025 1:43pm
Thank you for the explanation. I can't remember seeing a more beautiful full-suspension bike. Love the clean lines and the steel-tubing aesthetic. Thank you for sharing.
This bike check has 12 comments.
ThomDawley Added a comment about bike check Dawley T16
6/9/2025 11:38pm
Cheers! I imagine the Canfield frame is about the same weight as my T16, so it’s just part selection I reckon. I’ve got some really nice wheels and tyres that drop a fair bit (and make it accelerate like a rocket). With a more ‘standard’ trail wheelset and rubber my T16 would likely come in closer to 33.
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This bike check has 12 comments.
ThomDawley Added a comment about bike check Dawley T16
6/6/2025 10:42am
Cheers mate! Brief when designing this one was just to squeeze a shock into my hardtail design. Turned out better than I ever imagined!
This bike check has 12 comments.