Would a trispoke or flatter disc tend to be better at low yaw because the “spoke” essentially presents zero exposure to frontal area?

Looking head on at a spoked wheel you see, well, spokes. Head on at a trispoke you see nothing but hub and tire.

Would a trispoke or flatter disc tend to be better at low yaw because the “spoke” essentially presents zero exposure to frontal area?

Looking head on at a spoked wheel you see, well, spokes. Head on at a trispoke you see nothing but hub and tire.

Well drag is directly proportional to frontal area so if all other things were equal, which isn't a given, then yes it would be faster. The BikeTechReview video is interesting because as they change to yaw of the trispoke to about 5 degrees it starts to actually turn forward. So the airfoil of the spoke (probably at the top of the rotation) generates sufficient lift to overcome the bearing drag.

A trispoke definitely has some advantage over a traditionally spoked wheel, but I don't know how many people actually know or are willing to spill the beans. You can buy the BikeTechReview reports. I bought one a few years back, but even those don't tell the full story because they are wheel only tests and fork interaction is supposed to be a key factor.

But I'm wondering if anyone has seen any testing done on how many watts it takes to simply rotate different wheels at speed?

Here's the only comparison I've seen.

It's difficult to measure properly. That video of the Hed 3 spinning in the tunnel is meaningless. It needs to be spinning at tunnel velocity.

Here is my thinking on this... Rotational drag is primarily a byproduct of the translational drag being asymmetric. There is more drag at the top of the wheel than the bottom, because the top of the wheel will have a much larger relative speed to the wind. At the very top it's 2x wind speed. At the very bottom it's 0x. This drag asymmetry resists the wheel spinning forward (negative Torquemada), resulting in extra drag.

It's difficult to measure properly. That video of the Hed 3 spinning in the tunnel is meaningless. It needs to be spinning at tunnel velocity.

Here is my thinking on this... Rotational drag is primarily a byproduct of the translational drag being asymmetric. There is more drag at the top of the wheel than the bottom, because the top of the wheel will have a much larger relative speed to the wind. At the very top it's 2x wind speed. At the very bottom it's 0x. This drag asymmetry resists the wheel spinning forward (negative torque), resulting in extra drag.

I don't recall ever seeing reliable and sensible data on this. The Hed 3 spokes have way more frontal area than typical steel aero spokes, but they are airfoil shaped, and in line with the rim. The last feature might be significant at very low yaw. But the drag reduction from that will also show up in translational numbers, and the H3 is good but not great at low yaw. If the Hed 3 has an advantage in rotational drag, I'd expect it to be related to lift generated from the spokes. If you imagine a spoke at the top of the wheel moving through the air at >bike speed, the lift vector would be mostly to the side, but also forward a bit, counteracting the drag force. But... this phenomena would also reduce translational drag, and the Hed 3 doesn't do that well in translational drag compared to other good deep wheels. And you will always have a much greater side force when there is lift, which will upset steering, particularly if you transitioning back and forth between lift and no lift.

The results below are pretty typical I've what I've seen for Hed 3 translational drag. Based on that, I'm just not seeing a compelling reason to believe that any supposed reduction in rotational drag at higher yaw is happening, or if it is, it's compensating for the poor translational drag. And at low yaw it's good but not the best choice either.

Any recommendations?

You do realise the chart you have supplied is for a Hed 3D that had a very limited yaw window where it was marginally better than a Hed H3 but the H3 killed it as yaw got higher?

Here's the only comparison I've seen. The savings appear to not be trivial and definitely call into the question the industry's "Yaw is everything" mentality.

rruff wrote:

Shambolic wrote:

You do realise the chart you have supplied is for a Hed 3D that had a very limited yaw window where it was marginally better than a Hed H3 but the H3 killed it as yaw got higher?

One is, one isn't.

Show it.

True but even more complex than that. To truly measure it you need to vary tunnel speed, rotational speed and yaw. Think about trying to simulate a 40 mph tailwind on a wheel traveling 20 mph. In that case the relative velocity is 0 at the top and 2X at bottom.

https://www.sgvbicycles.com/products/hed-h3d-trispoke-90mm-clincher-html?variant=32749141455