So it seems yaw angle has been tested ad nauseam. But I’m wondering if anyone has seen any testing done on how many watts it takes to simply rotate different wheels at speed? The reason I ask is I’m curious if given the fact that the Jet 9 performs better than Hed 3 in most yaw angles is it in fact a slower wheel due to more exposed and less aerodynamic spokes, especially at higher speeds(around the 27-36mph).
Search on the Aeroweenie website. There is a paper their on wats to spin and it is the only published study I am aware of. BikeTechReview also has a video for negative watts to spin. Specialized did some testing , but they have been pretty tight-lipped about results.
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.
In terms of translational drag those two differ. Discs have almost all their benefit at higher yaw, though can marginally beat all other wheels at zero yaw. Tri-spokes, on the other hand, tend to suffer at higher yaw relative to modern deep aero wheels.
In terms of “watts to spin” I’d speculate that drag is largely independent of yaw angle, and mostly just a function of the rotational velocity of the wheel. But yes, discs and tri-spokes would have fewer watts-to-spin than spoked wheels.
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.
Is that the Trispoke tire video?
http://biketechreview.com/forum/1-general-discussion/26543-negative-watts-to-spin
I am not sure the video is still avaiable, but the thread with the discussion is at
.
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.
It’s not necessarily lift, but could also simply be the fact that the spokes have more drag when pointing down than when pointing up (i.e. reverse airfoil vs. airfoil). This will give a net torque on the wheel making it roll forward (if it’s higher than the force from the bearing drag). This effect will disappear when the wheel is actually rolling the same speed as the wind (but you will still have the advantage of the spoke being slightly more aero in the top part where wind speed is highest).
But I’m wondering if anyone has seen any testing done on how many watts it takes to simply rotate different wheels at speed?
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.
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.
A back of the envelope calculation indicates rotational drag to be about 1/3 of the translational and the little experimental evidence I’ve seen has indicated 25-30%. Haven’t seen the NZL data just posted.
A youtuber (Ronald Kuba) just posted vids of his aero testing on the velodrome and in Boardman wind tunnel with same setup and he stated that measured CdA was the same across both. One would expect wind tunnel CdA to be a bit lower because it doesn’t capture rotational drag. That would place rotational drag as somewhere close to the error in CdA measurement.
Here’s the only comparison I’ve seen.
Yes, I’ve seen that also, but their rotational drag numbers seem too high to be realistic. It’s important to realize that the two types of drag are related. Most of the rotational component is due to the vertical variation in translational drag, so it cannot be higher, and it should in fact be much less. I could believe up to 50%. I think when this subject came up in the past Dr Coggan said he was privy to some data he couldn’t mention in detail, but the rotational drag was less than 20% of translational as I recall, for a spoked wheel. That number is a bit less than I’d expect.
Somebody with a stable position needs to take a H3 and a good spoked wheel out to the velodrome and spend a few hours doing ABABAB… etc testing. Put a 20mm Conti SS on both.
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.
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.
Something like a Notio Konect would be awesome for this.
Maybe something like it… that works better.
Any recommendations?
But I’m wondering if anyone has seen any testing done on how many watts it takes to simply rotate different wheels at speed?
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.
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?
Any recommendations?
Not yet.
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.
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.
If this is the case, are any companies advertising these other parameters as a selling point for their wheels? With everything so close nowadays, it seems like if a company had this data they would be putting it out there instead of marginally better drag for double the price.