Home Made Aero Spin Down Test of 2 Top Wheels
Moderator: robbosmans
-
- Posts: 622
- Joined: Fri Feb 10, 2012 4:27 pm
Gah. this is tough to explain without a diagram. I'm not referring to the drag on the WHEEL, but the energy required to sppin the wheel.
Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓ Broad Selection ✓ Worldwide Delivery ✓
www.starbike.com
davidalone wrote:Gah. this is tough to explain without a diagram. I'm not referring to the drag on the WHEEL, but the energy required to sppin the wheel.
Doesn't matter. You're totally wrong. The drag from every single spoke uses energy. For what you are saying to be true, the drag from spokes on one side would be inputting energy into the wheel and drag from spokes on the other side would be sucking energy from the wheel. This is self evidently impossible. It doesn't even make sense.
The spoke drags cancel out on the sense that spinning the wheels will not make the spokes push the whole wheel up, or down, or forwards or backwards - but they do all work to rob it of kinetic energy and slow down its rotation. You need to go learn some physics. Any physics. Otherwise just stop talking.
- cyclespeed
- Posts: 1134
- Joined: Mon Jun 06, 2016 8:45 am
Wow, a lot of emotion here!
Just to take a time out!
1. I am not trying to re-invent the wheel (pun intended)
2. I am not looking to build a wheel company to take on Zipp, Enve et al.
3. Although I have a degree in mechanical engineering, a) it is from 1992 (i.e. old) and b) I do not claim to have any special knowledge of aerodynamics
4. I simply set out to compare two wheels' spin performances trying to focus on spoke drag.
5. I totally agree that this is not a 'real world' situation. As soon as the wheel moves forwards, the aerodynamics change. But this does not somehow magically anul the effects of aero spokes.
Just to take a time out!
1. I am not trying to re-invent the wheel (pun intended)
2. I am not looking to build a wheel company to take on Zipp, Enve et al.
3. Although I have a degree in mechanical engineering, a) it is from 1992 (i.e. old) and b) I do not claim to have any special knowledge of aerodynamics
4. I simply set out to compare two wheels' spin performances trying to focus on spoke drag.
5. I totally agree that this is not a 'real world' situation. As soon as the wheel moves forwards, the aerodynamics change. But this does not somehow magically anul the effects of aero spokes.
-
- Posts: 622
- Joined: Fri Feb 10, 2012 4:27 pm
wingguy wrote:davidalone wrote:Gah. this is tough to explain without a diagram. I'm not referring to the drag on the WHEEL, but the energy required to sppin the wheel.
Doesn't matter. You're totally wrong. The drag from every single spoke uses energy. For what you are saying to be true, the drag from spokes on one side would be inputting energy into the wheel and drag from spokes on the other side would be sucking energy from the wheel. This is self evidently impossible. It doesn't even make sense.
The spoke drags cancel out on the sense that spinning the wheels will not make the spokes push the whole wheel up, or down, or forwards or backwards - but they do all work to rob it of kinetic energy and slow down its rotation. You need to go learn some physics. Any physics. Otherwise just stop talking.
LOL. sure. okay. I really can't be bothered to explain online. But nevermind. Pretty damn sure I am correct in the way I mean it, even if you can't understand it. I have a master's degree in engineering, so, pretty sure my physics is sound.
davidalone wrote:LOL. sure. okay. I really can't be bothered to explain online.
I think you mean you can't explain it because there is no explaining it... because you're wrong. Or at the very least you've expressed yourself so incredibly badly that what you said is the opposite of what you meant.
Draw your diagram and we'll find out. Or answer this question - according to your 'cancelling' theory, if you span one wheel in a stand with bladed spokes set correctly and one wheel with baded spokes set 90 degrees crossways, would there be a difference in total drag slowing the wheel down?
I have a master's degree in engineering,
On current evidence, that's really depressing
Oh, wow, OP is still defending the test. Three words: Bearing Seal Drag.
I can spin my RZRs by hand and I guarantee it'll out spin both those wheels. Is that because Reynolds created the most aero spokes ever? Doubtful.
This test is about as bad as testing the aero properties of a crankset by the number of revolutions it achieves in a free spin. I think that's a fair analogy, no?
I can spin my RZRs by hand and I guarantee it'll out spin both those wheels. Is that because Reynolds created the most aero spokes ever? Doubtful.
This test is about as bad as testing the aero properties of a crankset by the number of revolutions it achieves in a free spin. I think that's a fair analogy, no?
- cyclespeed
- Posts: 1134
- Joined: Mon Jun 06, 2016 8:45 am
RyanH wrote:Oh, wow, OP is still defending the test. Three words: Bearing Seal Drag.
I can spin my RZRs by hand and I guarantee it'll out spin both those wheels. Is that because Reynolds created the most aero spokes ever? Doubtful.
This test is about as bad as testing the aero properties of a crankset by the number of revolutions it achieves in a free spin. I think that's a fair analogy, no?
If it's all bearing seal drag, care to explain;
a) why most speed is lost in the first 30 seconds. i.e. the speed curve is NOT linear, it plunges from 54km/h, then levels off. Bearing seal drag is linear. Therefore this does not compute......
b) why there was significant air turbulence noise (almost like a fan) from the Corima at high speed.
If the RZR really does have amazing bearings, then in a low speed test (i.e from 25km/h) it may well beat these two wheels, as at some point, at a certain speed, bearing performance is more of a factor than aero performance. I had estimated about 20km/h but that is guesswork.
But the real test would be a high speed one. How long would the RZR take to decelerate from 54km/h to say 40km/h (same inertia, same tyre). ? At these higher speeds aero drag must come into play. If you think not, and given that aero drag is a function of speed squared, at what speed would YOU say aero drag becomes important? 100km/h, 200?
Test may be confused but OP has nifty wheels, that's for sure
I actually like wheels that spin well in the stand, even if any advantage it indicates is mainly or even completely in the head. FFWDs IME spin a long time but I struggle to think they are better hubs than Boras. I remember Ksyriums almost stopping the moment you your hand off them LOL
I actually like wheels that spin well in the stand, even if any advantage it indicates is mainly or even completely in the head. FFWDs IME spin a long time but I struggle to think they are better hubs than Boras. I remember Ksyriums almost stopping the moment you your hand off them LOL
----------------------------------------
Stiff, Light, Aero - Pick Three!!
Stiff, Light, Aero - Pick Three!!
-
- Posts: 304
- Joined: Mon Jul 04, 2016 1:52 am
This is what happens when someone with no engineering background concocts a test. Embarrassing.
- cyclespeed
- Posts: 1134
- Joined: Mon Jun 06, 2016 8:45 am
GothicCastle wrote:
This is what happens when someone with no engineering background concocts a test. Embarrassing.
Does a degree in mechanical engineering (Kings College 1992) qualify as an 'engineering background'?
What is embarrassing exactly? The fact that I believe that the forces acting on a stationary spinning wheel are bearing and aero drag? And that drag increases exponentially as speed increases?
The fact that I think you should consider what the spokes are like in your aero wheel set up?
Please elaborate.
not everything that can be measured is worth measuring. And Ive a masters in competitive knitting, so I should know.
Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓ Broad Selection ✓ Worldwide Delivery ✓
www.starbike.com
Relax guys, don't get excited that much... Many of the 'scientific tests' done by renowned companies and cycling magazines are similarly, if not more, simplistic and many in this forum believe them as the absolute truth.
The aerodynammics of the spokes are definitely somewhere in the test but the truth is that nobody knows what is their actual contribution to the deceleration effect.
The aerodynammics of the spokes are definitely somewhere in the test but the truth is that nobody knows what is their actual contribution to the deceleration effect.