Weight Vs Aerodynamics -Wheelset Selection

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Weight Vs Aerodynamics -Wheelset Selection

Postby Krank » Wed Jan 30, 2013 3:47 am

Your views on this topic?

If you had the choice of buying a top end clincher wheelset for racing and training hard, which criteria would be your highest priority in selection - weight (less rim depth and lighter weight and less aero) or more aero (greater rim depth, heavier, more aero - but saved Watts)?


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by BNA » Wed Jan 30, 2013 5:24 am

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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby toolonglegs » Wed Jan 30, 2013 5:24 am

Aero trumps weight in almost every situation.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Krank » Wed Jan 30, 2013 6:44 am

thanks TTL.

can u elaborate on the science behind your statement.

i am interested to know why slightly heavier (but more areo) wheelsets are better than lighter ones - in your view?

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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby warthog1 » Wed Jan 30, 2013 6:50 am

They help you go faster everywhere except the steepest climbs.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby winstonw » Wed Jan 30, 2013 7:22 am

warthog1 wrote:They help you go faster everywhere except the steepest climbs.


At what speed do you think aero wheels provide an acceleration advantage?
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Alex Simmons/RST » Wed Jan 30, 2013 8:31 am

http://www.biketechreview.com/index.php ... erformance

aside from mass and aerodynamics, wheel choice factors include other things like durability, ability to stay true, lateral stiffness, cost, repair-ability and service cost, suitability for the purpose/race/riding situation, braking demands, handling characteristics, available tyre choices, bearing and freehub quality etc
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Alex Simmons/RST » Wed Jan 30, 2013 8:36 am

winstonw wrote:
warthog1 wrote:They help you go faster everywhere except the steepest climbs.


At what speed do you think aero wheels provide an acceleration advantage?

At all speeds above a track stand, or at all speeds that any regular rider might encounter.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby winstonw » Wed Jan 30, 2013 8:50 am

Alex Simmons/RST wrote:
winstonw wrote:
warthog1 wrote:They help you go faster everywhere except the steepest climbs.


At what speed do you think aero wheels provide an acceleration advantage?

At all speeds above a track stand, or at all speeds that any regular rider might encounter.


Evidence?
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby warthog1 » Wed Jan 30, 2013 9:43 am

Don't have any objective, only experiential. Alex has forgotten more stuff than my entire knowledge on the subject, so I'll leave it to him.

Edit: that is my way of saying he knows heaps more than me, for the pedants on the forum.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Krank » Wed Jan 30, 2013 6:57 pm

thanks - any other input?
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Krank » Wed Jan 30, 2013 8:35 pm

SES 6.7 enve rims
Alchemy ELF front hub
Alchemy ORC rear hub
Tubular
Sapim CX-Ray spokes

looking at above.....

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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby toolonglegs » Wed Jan 30, 2013 8:52 pm

Krank wrote:SES 6.7 enve rims
Alchemy ELF front hub
Alchemy ORC rear hub
Tubular
Sapim CX-Ray spokes

looking at above.....

krank


So we are talking top $$$ here ... and we are talking tubular now as well as you highlighted clincher in OP.
Personally I would be RATHER happy with that combo!... but I would not spend my time training on it, can't swap tubs over very easily between races and training. Personally I like near new tyres for racing.
So get a cheaper clincher for training?.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Krank » Wed Jan 30, 2013 9:05 pm

thanks TLLegs.

Honestly, I am not sure about Clinchers or Tubulars yet.

I read that tubs are very hard to install in event of a flat and you have to carry around a significant spare tire and glue in your gurnsey - as opposed to a smaller a tube for a clincher...

I understand that tubulars are lighter, but are they worth the reduced weight?


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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby toolonglegs » Wed Jan 30, 2013 9:22 pm

I am having a set built now 58/88 combo... they will be racing only. I will carry a pitstop bomb for punctures ( but punctures are rare where I live ). Long races I will carry a spare... I have seen guys change tubs as quick as you can change a clincher on the roadside.
I have tubs on my TT bike ( 88/Disc ) but have never ridden them on a road bike... keep hearing stories about how great they feel. So time to try.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Krank » Wed Jan 30, 2013 9:25 pm

thanks.

how will you be carrying a spare tire with you when you ride with the tubs? Bulky??

you have a link for the "pitstop bomb" for punctures?

ANd, dumb question - but do wheel decals affect aero in any way?

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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Bakks » Wed Jan 30, 2013 9:54 pm

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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby winstonw » Wed Jan 30, 2013 10:15 pm

Bakks wrote:Apparently they are bringing out a "proper" toroidal clincher in about a month. See http://velobuild.com/14-carbon-wheels/4 ... arbon-rims


Thanks. Didn't realize the composites were chiroidal, not toroidal.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Alex Simmons/RST » Wed Jan 30, 2013 10:33 pm

winstonw wrote:Evidence?

Umm, not sure I need any, it's just basic physics. Newton's laws of motion, and a bit of fluid dynamics.

Anything moving through air experiences a resistance force due to the air, and so if you have two similar objects, and one has "better" aerodynamics (e.g. by having a lower coefficient of drag and/or frontal area), then by its very nature, the one with the lower CdA requires less force to travel at any given speed through the air, and so clearly it will also use less energy to arrive at any given speed from a slower one.

Now if you are comparing objects that have a different masses (nothing suggests an aero wheel has to be heavier than a less aero wheel) or presents different moments of inertia, then one can also do the math, and you'll find that the difference then depends on how much the CdA of the system has been reduced compared to difference in mass, and the moments of inertia. You can pretty much discard the moment of inertia, as the difference in energy demand when accelerating bicycle wheels with a different moments of inertia is very small.

but let's consider an example, take for instance my rear Velocity Aerospoke 32 spoke standard bike track wheel and my Zipp disk. Not I don't know the weights precisely of each, but let's be generous and say the Zipp weighs 0.5kg more. It's nothing like that much heavier, but let's take worst case.

Let's also assume we have a bike + rider with the Aerospoke = 80kg.

And let's also assume they go from 0 to 50km/h in 10 seconds, which is a pretty solid acceleration.

Power required just to accelerate (not including all the other resistance forces - this is just power required to change kinetic energy so we can isolate the impact of different masses)
= 771.6W

Now let's add the 0.5kg to the system. Power demand for acceleration component is now
= 776.4W, or an extra 4.8W due to the additional mass.

OK, I know (because I have done the testing) that my Zipp lowers my system CdA by 0.023m^2 over the Velocity Aerohead. I also know that similar scale reductions in CdA are possible with similar deep section rims, such as 808 or 404. And that's just for the rear, not the front.

If I do an integration across that 10 second acceleration (and make an assumption of an even rate of acceleration, although it will under estimate the aero savings since the rate of acceleration will slow due to both neuromuscular fatigue kicking in after 5-6 seconds and the curvilinear rate of increase in air resistance during an acceleration), and compare the difference in power demand for overcoming air resistance, the more aero wheel saves me 11.2W for that 10 seconds, more than double the power "cost" of the over estimated mass increase. So a net gain there. And keep in mind I'm over estimated the mass cost and under estimating the aero benefit.

Now the aero savings are very small at the slower speeds at the start, and build up significantly as speed increases. If I had done same for an acceleration from say 30-50km/h over 5 seconds, then the saving due to the better aerodynamics during that 5 seconds is 21W and the cost due to extra mass is 7W. Net gain of 14W.

Then consider that once up to speed, the steady state power demand difference between the wheels at 40 km/h is 19W and at 50km/h it's 37W.

So not only does the heavier aero wheel reduced the net power demand during an acceleration from a standing start, it's also now significantly easier to maintain speed once you've stopped accelerating (which is most of the time), or indeed enables one to go faster for the available power. And if the starting speed is higher, the benefit of aero over weight during acceleration is even greater.

YMMV
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Xplora » Thu Jan 31, 2013 8:41 am

And the magic being that you can buy that wattage rather having to train for it ;)
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby simonn » Thu Jan 31, 2013 9:33 am



If you are going to be buying a set can you let us know how you get on with them? I am most interested, especially as the weight is within the same ballpark as my Mavic Ksyrium Equipe.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Xplora » Thu Jan 31, 2013 10:08 am

^^^^ hopefully some competitive pressure, or even rebranding, will put these rims on our bikes? I did note that Zipp has some yum cha import wheels.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby winstonw » Thu Jan 31, 2013 12:05 pm

Alex Simmons/RST wrote:Now if you are comparing objects that have a different masses (nothing suggests an aero wheel has to be heavier than a less aero wheel)


except maybe price, durability....and the title of the thread.

If your explanation covered all bases Alex, everyone would be riding discs, front and rear at 2+kg.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Alex Simmons/RST » Thu Jan 31, 2013 12:18 pm

winstonw wrote:
Alex Simmons/RST wrote:Now if you are comparing objects that have a different masses (nothing suggests an aero wheel has to be heavier than a less aero wheel)


except maybe price, durability....and the title of the thread.

If your explanation covered all bases Alex, everyone would be riding discs, front and rear at 2+kg.

Perhaps you missed my earlier post on this thread wrt factors involved in wheel choice :roll:

viewtopic.php?p=915616#p915616
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby twizzle » Thu Jan 31, 2013 12:28 pm

Thanks for the detailed explanation, Alex.
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