Home Made Aero Spin Down Test of 2 Top Wheels

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Zigmeister
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by Zigmeister

The noise and reverberation due to the rim being hollow affects the sound right? Spoke material/shape etc..so sound has nothing to do with this. Hence, why there are multi million dollar wind tunnels that can pretty accurately determine drag as that portion of the equation. Bearings/seals can be tested, and have been shown to only be maybe a watt or two at most. Also, tire friction has been shown/proven very well in several places. So we already know most of the equation/numbers related to drag/friction of wheels.

Not sure how spinning a wheel using noise and the length of time it spins is going to give us exactly how much drag/watts and time savings this translates into?

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cyclespeed
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by cyclespeed

I re ran the test using just the chuck of the drill, which measures 20mm radius. This gives 22.6km/h. This is 41.8% of the speed of the 1st test (54km/h). Thus, this slower test has less aero impact and more bearing.

If there were no aero drag going on at all in these tests, we would expect the spin time to be 41.8% of the 1st test, i.e. 2 mins 5 secs for the LW, and 1 min 15 for the Corima.

However, the results are; 3min27 for the LW, and 2min27 for the Corima.

This shows that deceleration is not linear. A non-linear force is affecting the wheel.

For consistency, I measured the time until the valve completely stopped, but I also measured the time for it to initially stop, and each time, for each wheel, this takes approx. 20 seconds.

Also, between the 2 test speeds there is not a doubling of total time, and yet there is a doubling of the advantage to the LW.

A slow test, (one small impulsion by hand - inaccurate, but hey), showed 40s Corima and 50s LW.

To my mind, this shows;

a) the bearings on the LW are slightly better (freeing rolling) that the Corima.
b) in this situation at least (static spin), the LW is more aero than the Corima.

Interesting further reading on this subject here; http://www.sheldonbrown.com/rinard/wheel/grignon.htm

lw11
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by lw11

So, at the end of reading five pages, what am supposed to have learned? And considering this test only has a sample oh two wheelsets, what does this mean for those not tested? If someone could explain this in layman' terms, that would be great!

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cyclespeed
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by cyclespeed

lw11 wrote:So, at the end of reading five pages, what am supposed to have learned? And considering this test only has a sample oh two wheelsets, what does this mean for those not tested? If someone could explain this in layman' terms, that would be great!


It would have been nice to have included a Zipp 404 or similar, but unfortunately I don't have one to hand at the moment.

I guess it just confirms what most people knew already;

a) aero drag becomes an important factor at high speeds, i.e. above 30km/h it starts to become an issue, above 40km/h it is by far the dominant factor, 50km/h +, well.....

b) free rolling wheel bearings are a useful addition to overall efficiency, but are far outweighed by aero considerations above a certain speed

c) given that your spokes are spinning at up to twice your cycling speed, and you usually have 40 or more of them, it makes sense to consider their shape, (thickness and profile).

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dj97223
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by dj97223

Leviathan wrote:not everything that can be measured is worth measuring.


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bm0p700f
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by bm0p700f

Well I have a shallow rimmed wheel 28 round spokes that spins for 4 to 5 minutes does that make it more aero than the wheels you tested? Well by the OP reasoning it does so he has wasted his money. My wheel is a Kinlin XR200 (£35 retail) 28 black sapim laser spokes not even £28 and a novatec A291 hub. So there you go OP by your test I have a more aero wheel that cost alot less.

In the real world it is not more aero though.

I still the OP needs to do the maths on this. if by this test you have concluded that aero drag is increasing important as speed increases then we all could have told you that. Aero drag for a rider on a bike is dominant on the flat above at 10 mph so I am not sure how this test has changed that fact.

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cyclespeed
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by cyclespeed

bm0p700f wrote:Well I have a shallow rimmed wheel 28 round spokes that spins for 4 to 5 minutes does that make it more aero than the wheels you tested? Well by the OP reasoning it does so he has wasted his money. My wheel is a Kinlin XR200 (£35 retail) 28 black sapim laser spokes not even £28 and a novatec A291 hub. So there you go OP by your test I have a more aero wheel that cost alot less.


I would guess;

a) your wheel has a much higher moment of inertia that mine, so takes more energy to spin up, and hangs onto that energy longer.

b) you may well have nice bearings that are relatively loose and allow long spin times.

One thing that has come out of this test is that below about 30km/h it is mostly bearings, above 30km/h it is more aero, but especially above 40km/h or so. I had expected the 'transition' point to be more like 20km/h, but seems it is higher.

Would be nice to have a big ass fan to blow air across the wheel at 50km/h for a more realistic result, but don't have one..yet!

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Calnago
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by Calnago

cyclespeed wrote:Would be nice to have a big ass fan to blow air across the wheel at 50km/h for a more realistic result, but don't have one..yet!

That would only blow your whole stand over with those Lightweights and wide flat spokes.
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bm0p700f
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by bm0p700f

Please get a fan and set to max and blow your stand over with those light weights and video/post that. I would watch that and laugh.

I am not normally this mean but 5 pages and the OP still does not get it.

Marin
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by Marin

It's similar to those "how long do my cranks spin" vids that are used to sell unsealed bearings :)

jsinclair
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by jsinclair

lol logged in for the first time in months to tell OP how stupid and pointless this "test" is

even if this were a some way valid experiment, and its not, whats the point of measuring aerodynamic drag of the spokes separate from the aerodynamic drag of the system as a whole, especially since in this case you have tested rims and spokes that are inseparable?

even as a test of bearing and seal drag this experiment is pointless because you haven't taken into account system weight and other variables

lol, just lol

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cyclespeed
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by cyclespeed

So further testing has shown that the LW's bearings are free er running than the Corimas and that aero affects are small below 25-30km/h.

1 impulsion test;

(all timing is now done until when valve 1st stops moving.)

LW 50s
Cor 40s

10mm test (11.5km/h)

LW 122s
Cor 91s

20mm test (22.6km/h)

LW 3min 07 - 3min 12
Cor 2min 07 - 2min 10

48mm test (54km/h)

LW 4min 43 - 4min 44
Cor 2min 48 - 2min 49

The LWs are about 2 minutes better than the Corimas at the high speed test. This 2 minute gain is made up of bearing and aero, but in what proportion?

The LW's time advantage in the slower tests is almost all due to bearings. If we extrapolate this LINEAR curve, we would expect something in the region of a 1m30 gain for the high speed test (+/- 10s). And yet the high speed test shows an advantage of 2 minutes. Therefore, there is some kind of additional aero gain by the LW's, which could be anything from a few seconds to 30 or so. Without dozens of different size wheels (45mm, 40mm, 35mm etc.) which I don't have and lots more testing, I can't be any more accurate than that. It's just an attempt to see if there is some tangible difference there.

To hobble the LW's I made a simple cardboard rectangle of 56cm2 (3.5 x 16), which I ziptied to a spoke.

Image

The surface area of the LW's spokes is 84.5cm2. I have no choice but to guess the Cd at about 0.1. Given that the card has a Cd way higher, we are therefore increasing the spoke drag significantly.

The results are;

20mm (22.6km/h) = 2min50, 2min53

compared to 3min10 ish, therefore not a huge drop, and just confirms that at this low speed test, aero has little impact.

However, the 48mm test (54km/h) is;

3m07, 3m15. A huge drop of over 1m30. Clearly at this speed the drag is much higher, and in the test, the speed drops off visibly very fast.

I then cut the middle section out of the card, thereby reducing it's area by 1/3.

37cm2 card high speed test = 3m28 and 3min29. Still a big impact, but moving back up.

I then cut each remaining piece of card in half.

18.5cm2 card high speed test = 3min58 and 4min

I then removed one piece of card and slid the remainder to the middle.

9.25cm2 card high speed test = 4min 21

Unfortunately I don't have a NASA approved wind tunnel to hand, so can't do similar tests in 'real world' conditions, but if it can be shown that Wheel A spins statically at high speeds (therefore aero affected) better than Wheel B, is it not reasonable to assume that it would therefore also be better in the 'real world'?

I guess the internet forum police can sneer all they like, but I'll be keeping the LW's in France for the flatter, faster stuff, and the Corimas* in Majorca for the hills. *also stiffer for climbing.

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cyclespeed
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by cyclespeed

FWIW, I placed the largest domestic fan that we have, as close as possible to the wheel, on full power, yaw angle 10', and this reduced the LW's high speed run from 4m45 to between 4m15 and 4m05, i.e. a drop of over 30 seconds.

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mrgray
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by mrgray

i think this was interesting but that's mainly, as somebody else pointed out, because i do ride rollers all the time (and typically want to get some miles up when i'm riding them to hit my weekly goal). for the easiest mileage - i recommend 80 mm boras. perhaps cyclespeed the thing that got some people a bit revved up was your contention that manufacturers have failed to take into account spoke characteristics, which i think you'd agree in hindsight is unlikely.

instead i am led to believe based on a sifting of the various replies, spoke shape is not the world's most important thing (for a wheel on a bike that is actually moving (i.e. not on rollers) because at its peak velocity (relative to air) it is trailing the rim? but then i presume it does become relatively more important for a non zero yaw situation? also bladed spokes are probably not really a great idea in real world situations because of non-zero yaw?

all i know is that my lightweights look awesome and run great except in real gusting winds when they can really give me the heebs.
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cyclespeed
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by cyclespeed

mrgray wrote:i think this was interesting but that's mainly, as somebody else pointed out, because i do ride rollers all the time (and typically want to get some miles up when i'm riding them to hit my weekly goal). for the easiest mileage - i recommend 80 mm boras. perhaps cyclespeed the thing that got some people a bit revved up was your contention that manufacturers have failed to take into account spoke characteristics, which i think you'd agree in hindsight is unlikely.

instead i am led to believe based on a sifting of the various replies, spoke shape is not the world's most important thing (for a wheel on a bike that is actually moving (i.e. not on rollers) because at its peak velocity (relative to air) it is trailing the rim? but then i presume it does become relatively more important for a non zero yaw situation? also bladed spokes are probably not really a great idea in real world situations because of non-zero yaw?

all i know is that my lightweights look awesome and run great except in real gusting winds when they can really give me the heebs.


Nice to see a balanced reply that isn't foaming at the mouth.

I don't think I ever said that manufacturers haven't taken spoke design into consideration. On the contrary, I think they take it very seriously.

Full carbon wheels like the LWs/Corimas have to use relatively large spokes as carbon cannot yet safely be made into a thin a spoke as a metal one. Making a bladed spoke is more complicated than just using a normal round one.

Corima improved their MCC design recently to make the front spokes more elliptical (as opposed to round). But the rear is still fully round, a shape that does not have a good Cd. So had I been testing rear against rear, the Corima would presumably have suffered more.(disregarding bearing drag).

When you ride on rollers, I think we can agree that you are putting energy into keeping your wheels spinning; at low speeds, mostly bearing, at high speeds, there is an aero factor too. That's all I'm looking at, albeit without scientific equipment.

A spoke's aero performance will be a function of it's surface area and it's Cd. Big round carbon spokes will therefore fair relatively poorly.

Things get more complicated at high yaw angles as side forces and more turbulence will be created.

I would say the best type of spoke aerodynamically is something like the CX-Ray. Thin and bladed, but not too thick side on.

MAvic's R-Sys wheels were well received (once they strengthened the carbon spokes) but was often criticized for the lack of aero performance of it's spokes;

"If there is one area that R-SYS could be criticized, it would aerodynamics. The carbon fiber spokes are round and fairly big, and do not fare as well as bladed spokes in wind testing. This will be of varying importance to you depending on the type of riding you do. If you are a competitive road racer with a penchant for the solo break, you might think twice. But for anyone else that recognizes that the biggest aero disadvantage your bike has is you, the R-SYS SLs are worth a look".

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