Weight Vs Aerodynamics -Wheelset Selection

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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Alex Simmons/RST » Tue Feb 05, 2013 5:12 pm

Xplora wrote:
Alex Simmons/RST wrote:http://alex-cycle.blogspot.com.au/2013/02/the-sum-of-parts.html

BWAHAHAHA If your event lasts less than 6 seconds, get the lighter wheel.

I think the real question is how much does 500 grams affect you on a 5 and 10 percent gradient, because gravity is the key. What is the 0/30 acceleration for 1000W on these gradients? What is the difference in speed and distance?

Of course, and my examples were specific to flat accelerations (since that's what was being "discussed").

When climbing one needs to account for changes in potential energy when making such comparisons. Gradient is already in the models, in these examples I just set it to zero. If you want to play with your own numbers, you can go to Tom Compton's site and knock yourself out. :)

On another day perhaps I'll do more examples of different scenarios, (certainly it's possible to feed in a detailed course profile and run the models over that) but really I have little need for that, I already have models for detailed time trial and triathlon bike leg pacing assessments (both for pre-race pacing strategy development and post-race pacing assessment) and the contribution of kinetic energy variances variances is pretty trivial in such events, and my models have stood up well when compared directly with time trial power files from professional riders to club amateurs. For the former I used data from David Millar and Marco Pinotti, who kindly make such data available.
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by BNA » Tue Feb 05, 2013 5:14 pm

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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Alex Simmons/RST » Tue Feb 05, 2013 5:14 pm

jcjordan wrote:As far as I can see Alex is supported by ENVE. They push there wheels, especially the deeper ones, as being suitable for climbing.

Just to be absolutely clear for everyone, I have no association with ENVE nor any wheel manufacturer.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby ironhanglider » Tue Feb 05, 2013 5:53 pm

Despite the naysayers I can happily accept that aero beats light in nearly every condition that my wheels experience. However I wonder what the real aero benefit is for me. The last pair of wheels I built for myself were intended for crit use. I used low profile tubular rims with not much more depth than the brake track, and 32 PG round spokes. This might not be the ideal setup for performance but they are for me.

I'm too lazy to look up whether you have any results for my situation but I'm not the sort of rider who likes to breathe fresh air. I'm happy to let the bloke in front of me worry about being aero. What swung the equation for me was that the rims are unpopular so I got them from eBay for $40 I got Novatec hubs cheap as well and I was able to use some spokes I already had (even though I had to do the front wheel 1x) and built up a fine pair of wheels for about $80. They are round, straight and I'm not going to cry if they get mangled in a crash. The real question is how many dollars do I have to spend to save how many watts in dirty air?

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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby thearthurdog » Tue Feb 05, 2013 7:25 pm

TDC wrote:
thearthurdog wrote:Aero, or light, it doesn't really matter. In the end the critical thing is that your wheels make that 'wo wo wo wo' noise. If they do that, you will fly.


erg...my heavy and non aero 32 spoke box section rim wheels make that noise. So...confused!


No you are getting 'wo wo wo wo' confused with 'wup wup wup wup'.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby jcjordan » Tue Feb 05, 2013 8:09 pm

Alex Simmons/RST wrote:
jcjordan wrote:As far as I can see Alex is supported by ENVE. They push there wheels, especially the deeper ones, as being suitable for climbing.

Just to be absolutely clear for everyone, I have no association with ENVE nor any wheel manufacturer.

Sorry Alex I did not intended to link your with ENVE wheels.

My point was that their published finding on the website support your statements that unless you are going up a very steep incline aero wheels provide benefit that outweighs the weight cost.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Xplora » Tue Feb 05, 2013 8:36 pm

Tom Compton's site is quite illuminating. You don't seem to get any "weight" advantages until you hit 8.5% gradient. Those are some pretty serious climbs... and I'm guessing if you are racing, you could expect some flats and downhills with those climbs... which would propel the aero rider way in front of the light rider... you'd have to give up some serious weight over your competition in the wheels for you to choose a light wheel over an aero one. If you could choose, I think a 404 (60mm) pair of wheels would sort you out unless you were attacking stupid climbs all day. Even then.... the rider with the bigger frame cannot hope to beat the skinny guy without pushing a lot of extra watts.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby winstonw » Tue Feb 05, 2013 8:46 pm

Alex Simmons/RST wrote:More red herrings and non-sequitur.

Have you anything constructive to add?


Alex, I'll keep your blog charts in mind every time I'm cycling windless flattish environs. :D

Meanwhile, I look forward to your blog models accounting for unstable aerodynamics, steering torque, and hills.

As for the gallery, I look forward to their 2013 anecdotes telling how all year round, they raced ultra-aeros.....and I'll be sure to avoid them as they struggle to come to terms with the steering torque required to hold an efficient race line. :roll:
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby mjd » Tue Feb 05, 2013 9:00 pm

winstonw wrote:
Alex Simmons/RST wrote:More red herrings and non-sequitur.

Have you anything constructive to add?


Alex, I'll keep your blog charts in mind every time I'm cycling windless flattish environs. :D

Meanwhile, I look forward to your blog models accounting for unstable aerodynamics, steering torque, and hills.

As for the gallery, I look forward to their 2013 anecdotes telling how all year round, they raced ultra-aeros.....and I'll be sure to avoid them as they struggle to come to terms with the steering torque required to hold an efficient race line. :roll:

Another fantastic contribution!
When doing rolling paceline as stated in another topic for 80km at 45kph am curious to know do you use aero or not ? Or is that just torque I mean talk.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby twizzle » Tue Feb 05, 2013 10:03 pm

I never realised that wheels only came in 12-spoke 600gm 50kg-riders-only and 2Kg disc with nothing in between.

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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby ausrandoman » Wed Feb 06, 2013 5:00 am

winstonw wrote:
Meanwhile, I look forward to your blog models accounting for unstable aerodynamics, steering torque, and hills.

As for the gallery, I look forward to their 2013 anecdotes telling how all year round, they raced ultra-aeros.....and I'll be sure to avoid them as they struggle to come to terms with the steering torque required to hold an efficient race line. :roll:


This is very interesting.

Can you point to any numerical data on the combinations of wind speed, direction and rim depth at which steering becomes aerodynamically unstable?

At what range of rim depths are the boundaries between non-aero, aero and ultra-aeros?

I'm looking for a new set of wheels and I would like to get something in the range 1400 to 1700 grams (as a rough guide, (1) I ride lots of 10% - 15% hills (2) most wheels lighter than about 1400 grams are over my budget). Being only 65 kg and 177 cm, I descend fairly slowly: I have a disadvantageous weight to cross-sectional area ratio that I can't change. I can buy a bit of aerodynamic assistance in the form of a pair of wheels but I don't like the idea of aerodymanic instability while hooting down at 70 kph in a cross wind.

So, wintsonw, would you please make a recommendation for maximum rim depth. I'd be most interested to see specific data on the threshold of steering instability for (as an example) a wind vector of 80 kph at 30 degrees. I realise that, while rim depth is the dominant parameter, it is not the only factor in aerodynamic instability.

Oh, and please define "aerodynamic instability" as it applies to bicycle front wheels. How is it different from being forced to steer downwind to maintain balance in a gust of wind?
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby thearthurdog » Wed Feb 06, 2013 6:36 am

winstonw wrote:As for the gallery, I look forward to their 2013 anecdotes telling how all year round, they raced ultra-aeros.....and I'll be sure to avoid them as they struggle to come to terms with the steering torque required to hold an efficient race line. :roll:


This won't be a problem. I can actually steer a bicycle.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Alex Simmons/RST » Wed Feb 06, 2013 9:07 am

winstonw wrote:
Alex Simmons/RST wrote:More red herrings and non-sequitur.

Have you anything constructive to add?


Alex, I'll keep your blog charts in mind every time I'm cycling windless flattish environs. :D

Meanwhile, I look forward to your blog models accounting for unstable aerodynamics, steering torque, and hills.

As for the gallery, I look forward to their 2013 anecdotes telling how all year round, they raced ultra-aeros.....and I'll be sure to avoid them as they struggle to come to terms with the steering torque required to hold an efficient race line. :roll:

I think it's time you published your models. The gallery awaits.

Unstable aerodynamics? What exactly do you mean by this? Be precise in your definition.

Steering torque? Seriously? If you have trouble steering a wheel due to steering torque variances in wheels that are commercially available, then I'm afraid you have much bigger problems.

Perhaps you mean suitability of wheel choice when facing cross winds or variable wind conditions? I can't tell from your choice of words if that's what you mean or something else. If so, that's clearly a consideration one needs to account for (and is on the wheel choice list under "suitability for the purpose/race/riding situation" and "handling characteristics"). I have never said otherwise.

I mean take a time trial scenario. Most competent TT riders will ride a rear disk in almost any wind conditions, but they will typically vary their choice of front wheel to suit the conditions (my confidence limit was a rear disk and front 40mm deep wheel in 60km/h cross head/tail wind with 100km/h gusts, I wouldn't ride a deeper section front rim in those conditions. A different/lighter rider however may struggle with such a combination in such conditions). There are many factors at play when making these choices, e.g. rider weight, bike set up, rider experience for instance. In a road race, the factors to consider are different again and naturally what I would choose there is different.

Hills? Sure, as I've said many times already, gravity is another factor and I was discussing the flat acceleration scenario because, as you know, that's what I was asked about. The fact that it's also a factor we experience in most track and crit racing is a fringe benefit.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby boss » Wed Feb 06, 2013 9:47 am

Stop feeding the trolls doods.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby __PG__ » Wed Feb 06, 2013 12:56 pm

Alex Simmons/RST wrote:http://alex-cycle.blogspot.com.au/2013/02/the-sum-of-parts.html

I'm crunching some numbers to see what sort of theoretical improvements I can get out of a carbon tubular wheelset for a hillclimb. How easy is it to track down real Cd/intertia numbers for Zipp/Enve rims?
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby ausrandoman » Wed Feb 06, 2013 2:18 pm

__PG__ wrote:
I'm crunching some numbers to see what sort of theoretical improvements I can get out of a carbon tubular wheelset for a hillclimb. How easy is it to track down real Cd/intertia numbers for Zipp/Enve rims?


Track down real numbers? That's 20th century fascism. In the 21st century, we each choose our own reality then select number to justify it.

Now to get serious ...

Your theoretical improvement is relative to what? If you are looking for a fine distinction between aero rims of similar construction and weight, you might have a hard time getting reliable data - and what looks like reliable data might be advertising copy. (In the 21st century, we ...)

On the other hand, if you want to compare wheels that differ in weight be a few hundred grams and in depth by a few centimetres, generic data for wheels of similar weight and depth to your two test cases might be a good enough guide.

See, for example

http://www.analyticcycling.com/WheelsConcept_Disc.html

http://www.southampton.ac.uk/~aijf197/Wheels.pdf

I hope you will share your results with us :)
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby mrgolf » Wed Feb 06, 2013 4:12 pm

So in a nutshell, a lightweight set of aero wheels is your best bet. /thread.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby twizzle » Wed Feb 06, 2013 4:22 pm

Yeah - lets lock this sucker. :twisted:
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Alex Simmons/RST » Wed Feb 06, 2013 5:31 pm

mrgolf wrote:So in a nutshell, a lightweight set of aero wheels is your best bet. /thread.

Depends on what's important. You may not wish to spend that much, or you expect to ride on rough surfaces, and so on...
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Alex Simmons/RST » Wed Feb 06, 2013 6:10 pm

__PG__ wrote:
Alex Simmons/RST wrote:http://alex-cycle.blogspot.com.au/2013/02/the-sum-of-parts.html

I'm crunching some numbers to see what sort of theoretical improvements I can get out of a carbon tubular wheelset for a hillclimb. How easy is it to track down real Cd/intertia numbers for Zipp/Enve rims?

Cd is tricky, as it depends on a few things, and typically varies with yaw and where on a bike it's used (obviously a rear wheel is dealing with some different air flow issues than the front wheel). Been a while since I've seen an updated table of wheel aero comparisons. There was one done about 5 years ago by http://www.rouesartisanales.com/ and they also measured moment of inertia for many wheels available at the time, but IIRC they don't provide values for Cd or I, but rather estimated power demand differences (unfortunately - although one can determine an equivalent change in Cd).

As for moment of inertia, well it's possible to set up a rig designed to measure it (or a very good approximation) - basically a big pendulum with the wheel in a vertical plane as the mass at end of a long string, but need to be able to control the plane of the wheel to be the same as the plane of the pendulum swing, or another method is hanging a wheel in horizontal plane from a rod through the axle and set up like a torsional spring. Measuring the period of either can provide enough information to calculate moment of inertia.

Velonews have a rig, and they might provide such details when doing a wheel review, can't say I've looked beyond one table Zinn published, which shows the spread of "I" amongst various wheels is pretty small, for a kinetic energy factor that's pretty small to start with. He did have values for a Zipp 202.

But you can assume that most 700c wheels will be somewhere between 0.1225 kg.m^2 and 0.06125 kg.m^2, per kg of rim mass, with the former being with all rim mass at the outer edge and the latter a rim that extends all the way to the centre (i.e. a disk). Then add the moment of inertia for the hub, which will be an even smaller factor, by another couple of orders of magnitude.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby Mulger bill » Wed Feb 06, 2013 6:42 pm

boss wrote:Stop feeding the trolls doods.

:? Plural? I see only one...
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby mrgolf » Wed Feb 06, 2013 7:18 pm

2nd attempt at ending thread: So a 38mm lightweight wheelset would be a decent compromise... /thread.
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby toolonglegs » Wed Feb 06, 2013 7:32 pm

Why end the thread... apart from W's clippety cloppiting this thread now has a wealth of information :D .
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby skull » Wed Feb 06, 2013 7:49 pm

toolonglegs wrote:Why end the thread... apart from W's clippety cloppiting this thread now has a wealth of information :D .


I know, if it wasn't for this thread I wouldn't know the wu wu wu sound means fast.

8)
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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby twizzle » Wed Feb 06, 2013 7:49 pm

True - now the noise has quieted down, it's a lot more interesting,


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Re: Weight Vs Aerodynamics -Wheelset Selection

Postby toolonglegs » Wed Feb 06, 2013 7:51 pm

skull wrote:
toolonglegs wrote:Why end the thread... apart from W's clippety cloppiting this thread now has a wealth of information :D .


I know, if it wasn't for this thread I wouldn't know the wu wu wu sound means fast.

8)


Well unless you are on your back in transition :P ... was thearthurdog's wheel still making that sound then? :mrgreen:
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