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The ride characteristics flex stay bikes give is subjective. Not everyone likes them which is clearly your point of view, but you don’t speak for everyone.
I have the flex stay Stumpjumper and an Evo. They both have their pros and cons. If I am riding a flow trail or something that’s not too rowdy, the flex stay feels awesome as you get so much energy back for what you put in. On the other hand it gets overwhelmed quickly in chunk and that’s where the Evo does better and if I had one, an Enduro would do better again.
Both are good bikes but have different use cases. I find myself picking the flex stay Stumpjumper more often as I enjoy the energetic feeling it provides.
One of the local XC racers who I worked with races U23 WC went to a training camp last year in europe with a flex stay bike and i started getting messages about how she should set up the suspension as her and her coach couldn't figure it out. She was racing on a medium frame, but she was over all just too light for the way the flex stay was tuned and she just could not get along with the bike. Allegedly, that bikes frame flex was tuned for 140-190ish expected rider weight for best results. So that bike just never worked for her no mater how she set it up. It was always harsh and bouncy no matter what she did.
a thin leaf spring is still a leaf spring.
Re: stumpy shock – Maybe that was my issue. Couldn’t stand the digressive shock for some applications and swapped to a stock tune when I blew up the RX tuned shock. I never did run them back to back… either way, EE should be flex stay, stumpy should be proper crab.
I think a lot of folks either don’t mind or don’t notice how crappy the flex stay bikes feel. If someone has a recommendation for a flex stay bike that’s especially well designed that I should test ride please let me know. But overall, whatever gains you’re getting by running a flex stay on an XC bike are not really worth the compromise on a proper trail bike. (My subjective opinion.)
Merida. Reviewed really well and realistically is fantastic - A bike I had in for testing, ended up buying it. seriously good.
thanks for this Jason.. so, if I understand correctly, with a linkglide setup ( 11sp XT derailleur/shifter, LG700 cassette), technically I could run xt di2 rear mech and shifter on my chain/cassette, right ?
btw I have been running the same cassette since Aug-2023, just changed the chain..amazing durability for LG stuff
What kind of maintenance was required?
when did you order them? mine got delayed way beyond what was initially communicated
The damping in the shock will still provide the same damping. Rather than looking at individual links and joints, think about what the suspension package is doing - it's providing a spring and damper system between the front triangle and the rear hub. Springs and dampers don't all have to be co-located (I think cannondale did a DH bike with that concept...) You just need to imagine the bike has two springs, one in the shock and a second on elswhere on the frame. You would maybe run a little less air pressure to compensate.
Cleaning and re-regreasing.
Mid January. IIRC raw Al pedals were delayed, black ones are shipping on time.
I can see how you might be correct on compressive forces (though I might also disagree based on the axis that the spring deforms not being in parallel with the damper?) but the rebound of the flex stay spring is for sure transferred undamped back into the axle. The damper will be controlling the shaft speed but the flex stay spring will be allowed to rebound unimpeded.
At the very least the flex stay equation depends on optimal/perfect shock performance, where a shock that is binding or has friction will decouple the flex stay from the effects of the damper. Also, if the flex stay is tuned to deflect at smaller forces than the shock can absorb, the damper won’t even be “activated” at all.
Flex stay can't rebound undamped. It doesn't move without the shock moving.
Nah.
The flex stay only moves a meaningful amount when the shock compresses. The flex stay can be modelled as a revolute joint with a torsional spring around it. If there is any angle change at that joint the shock will move. I've not checked out the kinematics but my suspicion is that the flex stays are only bending a couple of degrees so the effects are negligible anyway. The results people are describing could come from general suspension decisions.
To achieve what you're describing the shock would have to be very stiff compared to the rest of the frame and we'd see another portion of the frame deflecting in preference to the shock. Kinematically this would then no longer be a 4 bar linkage anyway.
This is derailing tech rumours a bit but the chattery feeling is almost certainly due to the effects on braking and not from the impact on the spring rate at the shock. Torsional revolute is the correct model but it's a fairly high rate. With a long lever arm (and a very small angular displacement) like a seat stay this results in low forces at the shock but it transfers big portions of the brake torque from the seatstay to the chainstay. Makes the braking much closer to a single pivot in feel.
And before someone else says it this conversation should move to a different thread 🙃
To keep the derail going, if you look at 99% of flex stay designs they are flexing maybe 2-3 millimeters tops. Take your rear linkage apart and you can flex the seatstays up and down with your pinky finger. There's very little resistance.
If you have a more novel design with meaningful spring to it, then the spring force is still acting on the damper and therefore affected by the damper.
as said before, the chattery feeling is almost certainly from going to a single-pivot-ish design from a Horst link. This is why I think the Cannondale flex pivot is better, although I've heard reports of them cracking so maybe not.
Thanks for insight about braking forces, I see now that this is a major factor, especially with my experiences on the two Stumpys.
I have to say though, the flex stay equation works when the bike is compressed and rebounds with the tires in contact with the ground. The problem is that when riding rough terrain the tire is leaving the ground (or maybe better put, the ground is falling away from the tire) faster at times than the shock is rebounding. At this point the leaf spring is going to unload faster than the shock, and when this happens over and over again over a section of chattery trail, you will feel very bad sensations coming from the rear of the bike. (And even if this is only a couple of mm of deflection, I think this can add up to a tremendous amount of undamped feedback into the bike.)
You guys are right, suspension tuning can play a role here, but I would rather not have to use a shock to tune out the flex stay chatter when there are more important things that the shock could be doing…
As someone who took part in a flexstay design project, I can confirm that:
- The spring force of the flex stay is minimal, relative to the spring force of the shock. As in it barely registers in a meaningful way to the ride quality of the bike. This was measured with instrumentation. The shock tune is all that matters here.
- We benchmarked the 2021 Epic EVO when we began our 2025 Rocky Mountain Element project, and yes that EVO frame rides stiff. There was a ton of trail feedback, and the anti rise that results from their flexstay design coupled with the stiffness of their RT made for a sporty experience when on the brakes. Their leverage curve (~18% progression), shock choice, and tune was also geared toward the XC racing side of things. As an aggressive XC bike, it performed exactly as such, but riders coming from the Enduro category might be left wanting a bit more compliance and comfort, and depth of travel.
Thanks for all the input, fascinating (to me at least) subject and let's move the discussion here: https://www.vitalmtb.com/forums/hub/flex-stay-discussion-thread
dammit i hate when someone else gets the last word in the Big Thread 😩
I figured since I kicked it off I should also move it 😀
32" wheel on a Lefty?
https://www.instagram.com/stories/romeandstuff/3659149975738703182/
Yeah and this makes me think about how the upcoming fox podium or other USD forks could easily be shimmed to fit a 32" wheel. The same thing I did to run a 29" wheel on my shiver SC.
Bad news for Di2 curious 11-speed LinkGlide lovers like you. This is a clarification about 12-speed vs. 11-speed XTR rear derailleurs, added to the XTR article after we published it due to questions from readers about 11-speed Linkglide options and clarification at Big Blue. Basically, no you can't use a normal M9250 battery-operated Di2 derailleur on a LinkGlide setup, only the M9260 derailleur that hardwires into e-bikes:
"The M9250 wireless derailleur is available for 12-speed Hyperglide+ drivetrains only, but can be used on normal bikes or e-bikes. However, there are 12 speed Hyperglide+ and Linkglide 11 speed options for e-bike only, but these M9260 derailleurs hard wire to the e-bike drive unit and can only be used with an e-bike, because they don’t have their own battery. There is compatibility between Shimano’s M9260 Di2 EBIKE rear derailleurs and Bosch, Shimano, and TQ drive units, with Shimano expecting expanded compatibility from other drive unit manufacturers in the near future.
So, there are no wireless derailleurs available for 11-speed Linkglide, only hardwire derailleurs for e-bike usage. And bad news for those wanting to hack a Linkglide M9260 Di2 RD onto a normal bike, it is unfortunately not possible to connect the e-bike Linkglide derailleur to the Shimano BT-DN300 battery for road bike Di2 systems. That means Di2 Linkglide is not possible without a compatible e-bike, unless you're ready to go rogue and MacGuyver a wired battery solution and maybe burn your garage/house/apartment down. This is not recommended by Shimano or Vital, or by your landlord, roommates, or romantic partner."
Someone, somewhere just thought, "Challenge accepted."
It is a dumb decision by Shimano, IMO. Instead of finally giving 11speeders a mainstream option, they chose the obscure route of proprietary design and complexity. I can't believe anyone will pick a Shimano-powered ebike just to have access to this RD.
Don't think it is limited to Shimano powered bikes, Avinox seems to support it too if other forums are correct.
Linkglide is so good on my cheat bike. I don't see why Shimano couldn't make their wireless RD's work with 11speed. Seems like a software and not hardware limitation.
They have software for the 11sp eRD, so it must be a business decision.
Rock Shox has a product launch next Wednesday, 6/25. Maybe a USD Fork??
32?!?