Home Made Aero Spin Down Test of 2 Top Wheels

Back by popular demand, the general all-things Road forum!

Moderator: robbosmans

Post Reply

RyanH
Moderator
Posts: 3185
Joined: Tue Jan 17, 2012 4:01 pm
Location: Los Angeles, CA
Contact:

by RyanH

I didn't listen with volume but this test is not indicative of anything. Bearing seal drag will have an influence on an unloaded wheel. If I did that test with my 404s vs RZRs, the 404s would come to a stop much sooner than both of your wheels and the RZRs would go almost the entire length of the video. That doesn't make one more aero than the other.

Sent from my SM-G930V using Tapatalk

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



User avatar
cyclespeed
Posts: 1120
Joined: Mon Jun 06, 2016 8:45 am

by cyclespeed

RyanH wrote:I didn't listen with volume but this test is not indicative of anything. Bearing seal drag will have an influence on an unloaded wheel. If I did that test with my 404s vs RZRs, the 404s would come to a stop much sooner than both of your wheels and the RZRs would go almost the entire length of the video. That doesn't make one more aero than the other.

Sent from my SM-G930V using Tapatalk


I would disagree.

At high speeds, the aero drag from the spokes, rim, etc. the wheel as a whole, is significant. You cannot simply ignore it. The noise alone coming from the Corimas shows that a lot of air is being moved. Maybe listen with volume? If you think spinning the equivalent of 2 x CD's through the air at 54km/h has no aero effect, then I fear you are mistaken.

If I was to rerun the test, but at a lower top speed (eg. 25km/h), then yes, bearing efficiency would play a much larger part.

wingguy
Posts: 4318
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

So you're testing how aero the spokes are and how good the seals are on two sets of wheels. Wow, that's fascinating. You know that rim and tyre weight will also play a significant role in your results here, right?

The test is meaningless and dumb.

Shrike
Posts: 2019
Joined: Fri Jun 03, 2016 5:08 pm

by Shrike

Aren't the tyres the same though, and the rim weights very similar. I think he addressed that in the video, no?

User avatar
kgt
Posts: 8749
Joined: Sun Jun 18, 2006 10:29 am
Location: Athens, Greece

by kgt

Not the most 'scientific' test but an interesting one nevertheless. I would like to see a Campagnolo Bora in comparison just for the fun.
IME all LW front wheels spin forever, that's for sure.

User avatar
cyclespeed
Posts: 1120
Joined: Mon Jun 06, 2016 8:45 am

by cyclespeed

wingguy wrote:So you're testing how aero the spokes are and how good the seals are on two sets of wheels. Wow, that's fascinating. You know that rim and tyre weight will also play a significant role in your results here, right?

The test is meaningless and dumb.


It's amazing how quickly people jump to conclusions without actually watching / listening.

I addressed the question of inertia in the video. The two wheels are very similar in weight, and although the LW is a touch lighter, most of that is in the hub. The tyres are exactly the same, even the same pressure.

So we can rule out the effects of inertia for the purposes of this exercise.

AJS914
Posts: 5397
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

To me this video creates more questions than it answers. Like:

What do those bearings do when loaded with 150-200 pounds worth of rider?

What was the speed the wheels ran at? Typical cycling speeds?

What was the point of measuring the Lightweight wheel bobbing back and forth. At that point, it seems like it's a test of the bearing seals.

User avatar
cyclespeed
Posts: 1120
Joined: Mon Jun 06, 2016 8:45 am

by cyclespeed

AJS914 wrote:To me this video creates more questions than it answers. Like:

What do those bearings do when loaded with 150-200 pounds worth of rider?

What was the speed the wheels ran at? Typical cycling speeds?

What was the point of measuring the Lightweight wheel bobbing back and forth. At that point, it seems like it's a test of the bearing seals.


OK, to take these in order.

1. Obviously, when loaded up, the bearings will create more drag, more resistance to motion, but not dramatically so. But this extra drag would be very similar for both wheels, and besides we are trying to look more closely at the aero drag, hence the high speed involved. If you load the wheel, you then load the tyre and bring tyre hysteresis into it, which just blurs the data. But if you DID do all that, then I would expect the spin time for both wheels to reduce by similar amounts, i.e. the conclusion would not change.

2. This is given in the video, both verbally and in writing; 54km/h. The polishing wheel on the drill is there for a reason; without it, you cannot get the wheel up to a high enough speed. Without the polish wheel, just using the drill chuck (20mm radius) you get about 25km/h. Aero drag forces increase with the square of your speed, so as the wheel spins faster, the aero drag increases significantly. Hence the high speed involved. A good Cat 1 race can easily be at these speeds for sustained periods.

3. Both wheels were measured until they stopped completely. The out of balance valve will always end up at the bottom, creating a seesaw effect. I could have stopped timing as soon as the wheel actually stopped in one direction, but for both wheels, from that moment to completely stopping was about 30 seconds, so it changed nothing. Those last 30 seconds are so slow, that aero becomes negligible.

User avatar
Rick
Posts: 2034
Joined: Sat Aug 29, 2009 4:30 pm

by Rick

THe test is interesting, and probably has some relation to bearing quality, seal drag, and spoke drag;
But it is not really indicative of anything associated with the aerodynamic drag of a wheel in real use.

When spinning a wheel in place, it is rotating in the steady state air 'field' of its own vortex.
When riding, the top of the wheel is moving at twice the speed of the bike, while the bottom of the wheel has a near zero velocity; and it is always moving into fresh, undisturbed air. There is also the question of loaded bearings, but that isn't part of the "aero" analysis.

{EDIT: So at the bottom of the rotation, the spoke aerodynamics is almost completely irrelevant, while at the top of the rotation, the spoke is moving into the 'shadow' of the tire/rim. In your test, the spokes are creating almost all the drag, while the rim has been almost eliminated, because it is moving into its own vortex.....all WAY different.}

Summary: Sort of a very flawed attempt. Not completely meaningless, but not conclusive of anything either.
So, if the goal was to "show" or "prove" the superiority of one wheel over another, that is a "failure".
Last edited by Rick on Sat Aug 27, 2016 5:39 pm, edited 1 time in total.

User avatar
DMF
Posts: 1062
Joined: Sat Dec 06, 2008 10:14 am
Location: Sweden

by DMF

But for crying out loud, you're testing wind resistance, WITHOUT WIND! Really, just sit down for a moment and contemplate yaw, even zero yaw. Yes you're test might have some validity in a 54kmh tail wind (but not really even then, not even by a long shot)... Otherwise, these wheels really aren't facing any actual wind, and the rims might be moving thru air, which is already circulating/rotating in the rims moving direction, but the wheels themselves as a whole are not by any means being pushed thru the wind.

User avatar
Calnago
In Memoriam
Posts: 8612
Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

Hmmm... I watched, I listened, I went away... I thought. And I come to the same conclusion as a few others here... Completely meaningless. If anything, it is much more about bearing drag than anything else.
cyclespeed wrote:...
If I was to rerun the test, but at a lower top speed (eg. 25km/h), then yes, bearing efficiency would play a much larger part.


What average speed do you think the wheel was spinning at during the entire test, including the back and forth pendulum swinging due to an unbalanced wheel. Why even include that phase? :noidea:
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

davidalone
Posts: 622
Joined: Fri Feb 10, 2012 4:27 pm

by davidalone

I am sorry, but your test is entirely wrong. Recommend you go learn some physics.

Relative velocity of your air relative to the wheel here is zero in this test since both are stationary.
Drag = 1/2 (rho)*u*CdA

where u is the flow velocity relative to the object.

your wheel in this case has rotational velocity and zero relative velocity to the air around it. There is a reason why wind tunnels test with moving air.

Because the wheel spins in a 360 degree circle, the minuscule amount of drag caused by the rotating spokes in the tangent direction of rotation is cancelled out by the exact same drag generated on the opposite side of the wheel. The amount of air drag that actually stops the wheel spinning is going to be extremely minusucule. the difference in bearing seals and wheel balance is the factor making up rotational losses.

User avatar
ergott
Posts: 2870
Joined: Tue Apr 18, 2006 3:03 am
Location: Islip, NY
Contact:

by ergott

This would be great if I were concerned with performance when I'm riding rollers.

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



User avatar
Calnago
In Memoriam
Posts: 8612
Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

I can't ride rollers without discs. Lol.
Apologies for being the first one to completely send this thread spiraling into the cesspool of irrelevance.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

Post Reply