CdA vs Power

[nobrakes]

So just a couple of months into my Cruzbike adventure and I’m already thinking of tweaking the V20....

I have the standard chainstay and a 45” xseam which puts the BB roundabout the same height as the bottom of the seat.

I haven’t tested CdA yet and am planning on some optimisation using the Chung method soon. I’m pretty sure a longer chainstay is going to be a consideration though.

However my local stomping grounds are like this: /\/\/\ so hill climbing is a significant part of any ride and I’m wondering how much of an effect raising the BB will have on my power. My suspicion is that I will lose a little off the top end. What say the hive mind?

 

[snilard]

So just a couple of months into my Cruzbike adventure and I’m already thinking of tweaking the V20....

I have the standard chainstay and a 45” xseam which puts the BB roundabout the same height as the bottom of the seat.

I haven’t tested CdA yet and am planning on some optimisation using the Chung method soon. I’m pretty sure a longer chainstay is going to be a consideration though.

However my local stomping grounds are like this: /\/\/\ so hill climbing is a significant part of any ride and I’m wondering how much of an effect raising the BB will have on my power. My suspicion is that I will lose a little off the top end. What say the hive mind?

My experience says that with lower angle between your torso and your legs you can produce more power. So you will get some power with longer chainstay.

 

[nobrakes]

With a longer chainstay, to keep the distance to the pedals the same I would lift the B.B. higher and closer making the angle more closed. This would be to get a more aero position with feet in the dirty air in front of the torso instead of pushing into the clean air stream going under the seat. So would you not lose a bit of power?

 

[LarryOz]

For me and from testing the wider the hip angle the more power can be made. Same athlete, same fitness. (I did a ton of testing between a V20 and S30). I ride an V20 now. Put me on an S40 and I will generate more power with same effort. Probably about 50watts. Great for going up hills faster, but bad for going down hills and on flats faster. On flat ground aero trumps power usually.

 

[nobrakes]

Thanks Larry. Makes it difficult to know if there will be a net benefit. Very little flat ground around here!

 

[Markopolo]

An opinion would be that there is quite a bit to be gained with doing something with the air coming off the back side. Compare the Cd of the tear drop vs. round object and the half sphere.

Couldn't post the link but wiki Cd and there are diagrams.

 

[snilard]

With a longer chainstay, to keep the distance to the pedals the same I would lift the B.B. higher and closer making the angle more closed. This would be to get a more aero position with feet in the dirty air in front of the torso instead of pushing into the clean air stream going under the seat. So would you not lose a bit of power?

Yes, I am saying that you will gain bit of power.