Longer chainstay = more speed

[Osiris]

Well you know better than me because you have done it. Now that you have said that... it's given me the idea that each knee goes through a different loci of points depending on chainstay. I still suspect the knees will go higher with a higher bottom bearing.

The maximum height of your knee relative to your shoulders is determined by the seat recline angle, the length of your torso, and the length of your femur. None of those variables are changed by raising your feet. Below is an animation of a study I did several years ago. It's purpose was to discover how to set up the pedals in a hypothetical velomobile to obtain the most compact aerodynamic shell. Increasing the height of the pedals naturally resulted in a more open knee angle during maximum flexion, but it had no effect maximum knee height.

 

[Gary123]

Catalyst pedals don't work well for me. I would love the mid foot position with cleats and a big pedal such as the catalyst. I have used the Catalyst pedals when on the trainer and definitely feel more power. My feet slip off when on tough hills and I have a hard time when starting out. I may try the use of toe clips to hold my heels in position. Someone has used toe clips in the heel position and reports that it works for him.

Have only used them on mb. With long spikes and soft sole they grip really well.

 

[ccf]

Something isn't making sense here. Going to a longer chainstay will only raise your feet. But how can raising (or lowering) your feet change your knee height relative to your shoulders?

As you raise your feet your entire leg will rotate upward. At some point your femur will be vertical (when your knee is maximally bent). If you raise your feet beyond that point, your knee (at its maximum bend point) will lower (not that this would be a practical riding position).

 

[bladderhead]

toe clips

Below are two pix of the Silvio pedals.



Below is the Grasshopper.




I am a bit scared of unclipping from clipless. I know what would happen if I got clipless and tried shoe-drilling. I would drill it wrong, try again, drill it wrong, so on until the shoes would fall to bits. Then buy more shoes and start the whole sorry process again, until I run out of money and you all see an advert on this forum for a (very) used Silvio in England. I was lucky to find old bits of ironmongery, like light-brackets etc that made a perfect fit. The Grasshopper ones incorporate the sawed legs of a metal table. The secret is to get the position of the toe-clips just right. You may think this is more hassle than shoe-drilling.

I can pull on the backstroke, but I cannot get power all round the arc. They are probably heavier than drilled shoes. They are a compromise between platforms and clipless. My feet do not fall out backwards, but it is really easy to get in and out of them. I never had a scary moment trying to put my feet down.

 

[Gary123]

Just curious is your pedal midfoot or forefoot placement?

 

[bladderhead]

Midfoot. If you want to ride on the balls of your feet you need to put more space between the toe-clips and the pedals.

 

[Gary123]

Thought so.

 

[Osiris]

As you raise your feet your entire leg will rotate upward. At some point your femur will be vertical (when your knee is maximally bent). If you raise your feet beyond that point, your knee (at its maximum bend point) will lower (not that this would be a practical riding position).

I thought I'd put my overpriced engineering software to some good use, so I did the following analysis based on actual dimensions. It turns out that you're correct. Though it's mathematically possible to raise the BB without any change in hip angle, if we want to maintain the same distance as before from the hip joint to the pedals, then there will be a resulting decrease in hip angle and a corresponding increase in knee height at full flexion. In my case, going to a size Large chainstay increased the BB height from 26" to 31". Using my body dimensions, and assuming a knee angle of 165 degrees at maximum leg extension, this raises my knee height at full flexion by 1.67". It's too small a change for me to perceive when on the bike, but more interesting is the decrease in hip angle, which in theory should allow me to produce slightly more power.

 

[Charles.Plager]

We are all different sizes and for me, putting my boom level increased my drag. I was really surprised. I did a bunch of coast down testing with different chain-stays and picked what worked best foe me.

This.

Aerodynamics is just weird. It really is. And having educated guesses is great, but testing things all together is going to give you the best results.

The only other complication is: Some aero changes that give better aerodynamics will also have you produce less power. How these two things interact depends on where you are on the power/speed curves and how you are riding (e.g., lots of climbing compared to going down hill, power is more important than aero).