Loss of efficiency with Ritchey Flexlogic seatpost?

Hello all,

I have a Canyon Ultimate CF SLX with a Ritchey Flexlogic seatpost. I find the bike very comfortable and smooth during bad asphalt and paving stones, thats good. I also have another bike that feels a lot stiffer, but hard to say that this difference is due to the seatpost.
link: Ritchey WCS Carbon Link Flexlogic Seatpost / Carbon Bicycle Seatpost

But on the indoor trainer during the ride i see moving the seat post slightly, and my question is doesn’t this lead to a loss of efficiency? Iam not a heavy rider with 66kg and 180cm tall.

I found this review: Best soft-riding rigid seatposts for road, dirt, and gravel - BikeRadar

You see in this graph the seatpost is not as flex as the Ergon CF3 and Canyon VCLS 2.0:

But the Ritchey scores very good in vibration damping:

And the last question, is it better for a light person to get some flex compared to a heavier rider?

I have the Syntace and as you say, these seatposts really help out when the road gets rough.

I’ve noticed the additional movement on the trainer too and wondered the same thing. And mine isn’t the most bendy either.

However, for me, the gain in on-bike comfort without having to give up the attributes of my frame that I like is worth any negligible loss of efficiency on the trainer.

Not sure that helps or answers your question. A true forum response.

1 Like

Hi DXR, thanks for your reply.

To be clear, I am not concerned with efficiency loss on the indoortrainer, but outside on the road

1 Like

His statement still applies if you swap “on a trainer” for “on the road”.

“There is no free lunch” is a saying that nothing comes for free. That is no different than anything in engineering where every benefit comes with some associated cost. The challenge is understanding the pros/cons and how they impact the overall goal.

Devices like this that improve comfort almost always have some level of “cost” to the rider. That motion that aides in comfort also has the potential to degrade power transfer. Much like MTB suspension (although on a smaller scale), the motion from a flexy post may lose power, but it can be a net positive in terms of comfort. I may give the rider durability over time that offsets the power loss.

  • If you are riding mostly smooth roads and the effectiveness of the post is minimal, it is likely a net negative.
  • If you are riding roads with sufficient roughness, the post may well prove to be a positive overall.

It is easier to quantify the power transfer data while the rider comfort/durability aspect is much harder to define. As such, it is up to the rider to evaluate if and when something like this might make sense. There is no hard data that will prove out that you need X amount of rough roads to justify the Y amount of power loss.

1 Like

thanks! Really helpfull.

Does a lighter person need more suspension, because otherwise he will “bounce” faster than a heavier person?

  • That is a tough question.

“Suspension” generally consists of a flexible support (spring in many cases, where the post in this case acts a bit like a leaf spring) and some level of damping (method to control the rate of compression and/or rebound, usually oil damper in regular suspension or material selection in this case).

Higher level suspension may include ways to adjust the spring rate and/or damping rate. This is intended to handle things like rider weight and/or performance preferences.

A post like this doesn’t have any of that and is just a compromise design that is aimed to hit some functional range of rider and performance characteristics. Unless the post maker specifies things like a functional rider weight or things like performance relative to exposed post length, all we can do is guess.

But in a simple sense, all we know for sure is that the basic amount of travel and rebound action of these posts will be different between riders of different weights.

No chance. You could ride seatpost-less without it hurting your efficiency. Just because something flexes doesn’t mean it’s inefficient.

The carbon seat post is a spring and a bad damper - springs spread out the release, dampers convert that energy into another type or direction of energy. I think steel springs are 85-90% efficient and carbon composites are 60% -ish. In any case, without dampening (hysteresis) or inefficiency (also dampening), you’re not losing mechanical input.

Just because something is less efficient in isolation doesn’t mean it’s inefficient in the long view.
–The flex smooths PEAK stresses, lessening the strain on your muscles and tendons. You’re going to be able to ride longer because you feel less tired; you’re going to be able to sprint harder because you’ve lengthened the peak application of force on your body.

Just because it flexes doesn’t mean its flexing in all directions.
– It’s only going to flex down and a bit away. It won’t flex strait backward or upward while you push, but will if you’re pulling on the pedal.
– If you’re sinking during harder efforts, it’s because you’re engaging your muscles in a way that’s shortening your leg - the lower saddle is automatically moving to a more efficient position.

I’ve tried the PWN Coast suspension post and the Canyon VCLS seat post, neither of these are all that active with the bike on the trainer - that right there tells you it’s not hurting anything. I’d say there is no downside other than weight and cost.

1 Like

Depends on the type of suspension and the how the rebound is damped…very easy to do that with a suspension fork, harder to do with something like a seatpost.

But I think the differences we are talking about here are so small that they are meaningless compared to the increased comfort.

I have been riding a suspension seatpost for years on any rigid off-road bike I have…hardtail MTB, CX and now gravel. Unfortunately my 2 decade old USE seatpost gave up the ghost this summer (bushings crapped out) so I am now on the stock Cervelo SP. I can’t detect any increased efficiency, but I sure miss the extra comfort.


I have a similar Ritchey aluminum seatpost at home that I’m going to mount to see if I notice a difference.

Bouncing depends on dampening and a few other factors. You can and will bounce on a rigid seat post.
Every spring on that first ride outside, i bounce like a pogo stick after I get off the trainer for a few minutes - it has nothing to do with the seat post. I think we’ve all had that experience where we hit a bump while we’re pedaling somewhat hard in the drops and we bounce 3-4 times on the saddle after the bump punts us up in the air.

Some factors outside of the seatpost spring rate:

  • tires size & inflation
  • saddle construction
  • bike fit / power application
    -pedaling / movement rhythm
    -seat post material
    -seat post exposure
    -seat post flex design
    -seat post clamp design

Does a heavier person with the same seatpost exposure and saddle need a stiffer suspension/flex post? No. Even a super flexy one under a heavy dude is going to feel pretty good as long as the motion of the flex is good and there’s some damping in the system. The main thing would be the springs oscillation doesn’t match your cadence, the roads vibrations, or something other vibration and you don’t bottom out the travel hard.

1 Like

To be clear, the bike + seatpost rides really nice on the road and I don’t feel like I’m really bouncing on the saddle through the seatpost. I only see him bending slightly during the indoor trainer. Outside (and inside) i dont feel it.

It is bending because it needs to. Either that force would cause the seatpost to give a bit, your bum/muscles/tendons to absorb the force, or you to be forced forward. It’s not likely the force would travel to the pedals because the pedals have your body weight forcing them down - inefficiency would be you raised off the saddle.