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  1. #1
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    Seat Height Change & Power Increase

    After 2 years riding close to the same the same fit my MMP curve on WKO+ hasn't moved much. Small movement here and there but nothing drastic until recently. Long story short, I moved my saddle up 1.5cm (no change fore/aft) and rode some punchy group rides with 6 defined sprint points. The red dashed line (old power) shifted to the right and was replaced with that beautiful new yellow line (new max) between 5 seconds and 2 minutes . The increase in watts at 5s was 6.5%, 10s increased 14.1%, 30s increased 22.2%, 1m increased 13.6% and smaller gains until the lines merged again around 2m. At 4m there was a little bump of 3.2%...

    Looking at it from a time perspective I was able to hold the old wattage values a bit longer. Starting at 5s I looked at what the old wattage was and looked where the new line crossed that value and noted the time. I did this every 100W down to 2m and the increase in time was; approximately 60%, 60%, 84%, 50%, 48%, 21% 37% 40% and then about flat at 2m. It should be noted that while the % change looks big I'd just like to point out that we're not talking about huge numbers here so any change at all will look "large". But, paying attention to power and trying my best to improve for race season this improvement will go a long ways towards sprinting, bridging and breaking. Hopefully over time I can improve or see gains in longer metrics as well.

    Anyways, this is just anecdotal and JMO. Further, I understand correlation doesn't equal causation but, I'm definitely intrigued as I was originally fit a bit conservatively due to an injury. I've been hesitant to move off that fit as I've been doing ok injury wise. However, knowing I have room to move higher (knee extension was at 35 degree) I plan on moving off the old fit but in a slower and more conservative approach (3-5mm change at a time). It should be noted that with the higher position my fit was balanced and comfortable when I moved the saddle fwd 5mm (On the bike-Steve Hogg methodology) and no crazy knee acceleration or hip rocking at the bottom of the stroke (again Steve Hogg methodology).

  2. #2
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    1.5 cm is a lot. I wonder if the increase in power reflects the fact that our power increases as the leg straightens and you may have missed a bit of top end power by having the seat too low.
    My rides:
    Lynskey Ti Pro29 SL singlespeed
    GF Superfly 29er HT
    S-Works Roubaix SL3 Dura Ace
    Pake French 75 track

  3. #3
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    Quote Originally Posted by serious View Post
    1.5 cm is a lot. I wonder if the increase in power reflects the fact that our power increases as the leg straightens and you may have missed a bit of top end power by having the seat too low.
    With out a doubt. I think it's pretty well known seat height affect power the most. I just wasn't expecting such gains. Actually, the long story is I stumbled onto this by accident. Anyways, my previous fit wasn't necessarily too low. It may have been too low for optimal power output but it worked as far as a conservative starting point post injury.

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    I know Joe Friel recommends riders get a bike fit each season as we tend to evolve a bit over the course of the year ( ie: gain/lose weight, flexibilty). I have also raised my saddle 2cm after having a professional fit that served me well for two years. As I became more flexible from riding alot more I could more fully extend my legs and able to rotate my pelvis more forward thus enabling the glutes to kick in more. For me I have not noticed an increase in short duration power but rather in my ability to spin more smoothly which I feel has helped me push a bigger gear longer.

  5. #5
    wim
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    Quote Originally Posted by woodys737 View Post
    I think it's pretty well known seat height affect power the most.
    Not really. Much has been written about saddle height, but there's nothing out there seriously correlating saddle height with power (watt). There's a strong and easily measured correlation between leg extension and force (newtons). But since power is a measure that involves force and time, force alone doesn't translate cleanly into power on a bicycle.

    There's also the complication of how the force is applied. As an extreme example, imagine a huge amount of force on the pedal at bottom dead center, which corresponds to maximum leg extension: it's completely useless to forward propulsion.

  6. #6
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    Quote Originally Posted by wim View Post
    Not really. Much has been written about saddle height, but there's nothing out there seriously correlating saddle height with power (watt). There's a strong and easily measured correlation between leg extension and force (newtons). But since power is a measure that involves force and time, force alone doesn't translate cleanly into power on a bicycle.

    There's also the complication of how the force is applied. As an extreme example, imagine a huge amount of force on the pedal at bottom dead center, which corresponds to maximum leg extension: it's completely useless to forward propulsion.
    Thanks Wim. I do appreciate your insight and you always give me more to think about that I hadn't considered. I've been looking at this for years and seem to run across studies such as this abstract HERE.

    Since I can't really measure how and where I apply force I just have to go on observations of power which seem to be in line with higher=more power (at least with in the 25-35 degree range).

  7. #7
    wim
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    Quote Originally Posted by woodys737 View Post
    I've been looking at this for years and seem to run across studies such as this abstract HERE
    Thanks, nice find in that it does address power!

    I've got a previous Will Peveler study here somewhere on paper (can't find it, of course!) in which he studied the effects of saddle height on economy only. The interesting thing for me about that study was the fact that saddle heights based on percentages (like 109% of inseam) can result in a wide range of knee angles. For example, one rider at 109% had a knee angle of 20 degrees while another rider at 109% had a knee angle of 40%. What surprised me was not that there is a variance, but that the variance is so large.

    The trouble with almost all of these studies is that they don't (more likely, can't) take the time to take adaptation into account. For example, a 2 cm change in saddle height is felt as huge and will most likely produce a significant change in economy and power. But what happens after three months of riding with that new saddle height? It would be good to have some information on that. Fascinating stuff, either way.

  8. #8
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    Quote Originally Posted by wim View Post
    Thanks, nice find in that it does address power!

    I've got a previous Will Peveler study here somewhere on paper (can't find it, of course!) in which he studied the effects of saddle height on economy only. The interesting thing for me about that study was the fact that saddle heights based on percentages (like 109% of inseam) can result in a wide range of knee angles. For example, one rider at 109% had a knee angle of 20 degrees while another rider at 109% had a knee angle of 40%. What surprised me was not that there is a variance, but that the variance is so large.

    The trouble with almost all of these studies is that they don't (more likely, can't) take the time to take adaptation into account. For example, a 2 cm change in saddle height is felt as huge and will most likely produce a significant change in economy and power. But what happens after three months of riding with that new saddle height? It would be good to have some information on that. Fascinating stuff, either way.
    Great question! Just guessing but, if the new position did yield more power, it's because the rider is recruiting either more muscles, the same muscles in a different way or new muscles not used before. If that's true then as you use those muscles they will only develop as you adapt and therefore yield better results (more power). I only say this from my own experience riding a tt bike compared to a conventional road bike...again just guessing.

  9. #9
    wim
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    Quote Originally Posted by woodys737 View Post
    as you use those muscles they will only develop as you adapt and therefore yield better results (more power).
    That would be my guess as well. But you can't ignore other parts in the kinematic chain, like tendons or ligaments. Over time, you might have to pay for that additional bit of power with discomfort or even an injury. It's all much more complex than many people assume.

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