lumping all betas and tires for both the 1080 and three spoke during these tests:
http://biketechreview.com/...trispoke-tire-choice
http://biketechreview.com/...458-1080-tire-choice
puts watts to spin at about 20% of total watts. there are some interactions at play with these data, though.

Thanks Kraig, awesome work! Guess I'm in the dark because I never bought your articles...

Did you ever publish your "back of the pickup" test data?

maybe we should back up a bit and challenge our assumptions.

I am assuming that "watts to spin" is measurable... say in a wind tunnel or other apparatus that can spin a wheel up to say, 50kph, with a knows Crr tire, and can than measure said energy required to spin wheel at 50kph.

energy to spin engine alone minus
energy to spin known Crr tire equals
energy to spin wheel

energy to spin wheel A minus
energy to spin HED 3 equals
watts saved (or lost) over state of the art spoked wheel

If this is true, then what we're measuring is watts to spin three very large in-line air foils vs. 18 very small out-of-line quasi-air foils.... right?

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Eric Reid AeroFit | Instagram Portfolio
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For our wind tunnel validation study, Jim Martin built a special F and R drive fixture out of an old bicycle frame and threw an SRM on it to measure the rotational + drivetrain power required when it was hand-pedaled in the tunnel (suspended above the floor) with the wind on. The same experiments were repeated with just hubs instead of wheels, with the rotational-only power requirement obtained by subtraction. A bit of a crude approach, perhaps, but the results were consistent with previous studies, i.e., the majority of the drag of a wheel is translational, not rotational, with little difference between wheels.

It should be measurable, but no one is doing it. At least not routinely. And the numbers appear to vary a lot, so maybe it's harder than it looks. Kraig was using balance data at LSWT, not motor data, but I don't know how he did it.

One thing to keep in mind is that rotational and translational drag are related. To compute rotational drag, you take the translational components multiplied by the ratio of their vector distance from the axle, divided by the wheel's radius. If the Hed3 and 808 have the same translational drag, then the Hed3 having less rotational drag means that its drag components are comparatively closer to the axle plane and less at the top of the wheel.

Is that right or am I missing something?

Because I'm getting more confused now. If the Hed3's airfoils improve rotational drag at yaw, then it should improve translational too. Since the airfoils are closer to the hub than the rim is, I'd expect translational to improve *more* than rotational.

EDIT: One thing just occurred to me. I've been assuming that pressure and friction drag are acting the same way, but that doesn't seem right. Pressure drag on the rim and tire won't be acting in the x-direction, but rather radially, and won't effect the rotational drag at all. Be warned! I really don't know what I'm talking about...

are you stomping your foot like a horse here? Or, is the difference between a tri spoke and a regular spoked wheel enough that they're not in the same family of "wheels" in your quote above.

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Eric Reid AeroFit | Instagram Portfolio
Aerodynamic Retul Bike Fitting

“You are experiencing the criminal coverup of a foreign backed fascist hostile takeover of a mafia shakedown of an authoritarian religious slow motion coup. Persuade people to vote for Democracy.”

This is my explanation:

When wind tunnel yaw is present, the part of the wheel below the hub sees a higher yaw because the velocity of the airfoil section is in the same direction as the wind. Even though the wind-airfoil relative speed is smaller (due to both the ground boundary layer and wheel rotation), near stall the drag coefficient increases significantly and the contribution of the lower part of the wheel on the rotation moment can become higher that the contribution of the upper part (that sees a higher wind-airfoil relative speed and but lower yaw so it may be in pre-stall conditions).

With this, the wheel turns forward.

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http://cds-0.blogspot.com

Are you thinking of why a Hed3 would start turning on its own at yaw? I'm not interested in that personally, since it doesn't relate to what happens when you are riding a bike.

If you are thinking of riding conditions, then a nice airfoil is going to create lift with a small forward component, once a little yaw is introduced.

My previous post was related to this. It shows how rotational drag can be reduced while translational one increases in yawed conditions.

This explanation is applicable in riding conditions or when the wheel starts turning on its own so I don't understand why you say that it doesn't relate to what happens whe you are riding a bike.

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http://cds-0.blogspot.com

Any plans to review the H3+? I'm developing an infatuation with that wheel and interested to see how it stacks up.

All the Cda of a tri-spoke, with lower Crr of a wide wheel?

Scott

My statement earlier was primarily to show that there is some inherent lack of axisymmetric flow for a forward moving, spinning wheel, and as ruff notes, that influence is not directly related to the longitudinal drag which is acting on the hub and tires and not producing torque on the wheel.

Regarding yaw, unlike in a (good) wind tunnel, gusts will have a boundary layer with respect to earth ground unless you are sliding sideways with your bike. So, I would suspect that even though what gusts actually affect the wheels will have higher relative yaw to rotational components, the absolute speeds may make the effect smaller. Maybe I shouldn't speculate so much here :P

Using the approach described, it was possible to detect a difference between regular 32 round spoke wheels, 24 bladed spoke wheels, and disks.

H3s (actually, could have been the original Specialized Ultralights, but same wheel) were also tested, but it wasn't possible to distinguish them from 24 bladed spoke wheels.

Power data were converted into an incremental drag area, as described in the paper:

https://www.academia.edu/...mech_1998_14_276-291

At 30 mph, it took approximately 2 W to rotate a single H3.

thanks, I'll dig through that when I get a chance. So you're saying H3 and 24 bladed spoke wheels are 2w to spin. Have you seen that data kicking around over at aeroweenie.com? I hesitate to even call it data to someone like you ;)

disc had rotational drag of 9 watts, tri spoke at 12 watts, Zipp 808 at 18 watts at 50kph



Watts at 50kph, Zero Yaw

Wheel Translational Drag Rotational Drag Total Drag

Mavic Disc 22.22 8.52 30.74

Zen TriSpoke 19.57 11.58 31.14

Mavic 5 Spoke 20.91 11.8 32.71

Zipp 808 20.01 18 38.01

Zen Wire Spoke 24.15 19.5 43.3

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Eric Reid AeroFit | Instagram Portfolio
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“You are experiencing the criminal coverup of a foreign backed fascist hostile takeover of a mafia shakedown of an authoritarian religious slow motion coup. Persuade people to vote for Democracy.”

Those SRM based watts to spin data were pretty much for entertainment purposes only...and I don't think my wife would have been able to collect on any life insurance had I continued pursuing this approach! ;-)



Not right now. It's an interesting wheel. Its' the only thing recently that has piqued my interest. However, I think folks would have to band together and fund the test so that I don't have any out of pocket expenses. Email me if interested in pursuing this.


I've seen a range of ~7w to spin across wheel/tire combinations and betas. The data i've collected also suggests the three spoke can have negative watts to spin at as little as beta=10.

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=================
Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
=================

Yes. As such things go, though, those results are an outlier. That is, there have been about a half-dozen investigations of the question over the years (including one a long time ago by Damon Rinard), with the vast majority of data indicating that translational, not rotational, drag dominates.

BTW, I calculated the "watts to spin" for an H3 wheel as:

0.5 * 1.185 * 0.00185 * 13.4^3 = 2.6 W (so closer to 3 W than the 2 I said before)

0.00185 is one-half of the incremental CdA we measured for a pair of such wheels in the tunnel.

hmmm....

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Eric Reid AeroFit | Instagram Portfolio
Aerodynamic Retul Bike Fitting

“You are experiencing the criminal coverup of a foreign backed fascist hostile takeover of a mafia shakedown of an authoritarian religious slow motion coup. Persuade people to vote for Democracy.”