wphamilton

I agree that fact that some wheels can create a positive force isn't the point - the fact that some can create a positive force for more than about 12°-15° of yaw is the point. The take from that is that some do, most don't. Greater yaw angles may be a net loss. By the same token, the fact that each produces some lift at small angles isn't the point. The point is what happens at greater angles of apparent wind.

The other guy made some generalities that I don't necessarily agree with but he raised another concern that I think bears thinking about: how important are these results outside of the wind-tunnel. I'm not one to dismiss wind tunnel data just because they don't replicate real-world conditions. I do like to consider what those differences in conditions are, and how the results might be altered under various real-world conditions. Maybe that's beyond the scope of discussion in this venue, but it is at least reasonable to say that the wind-tunnel shows the best case scenario, and under real world conditions the gains will not be as great as under ideal conditions.

asgelle

I think you're focusing on the fact that the curves are U-shaped at at some angle, the drag increases for a given wheel. I don't think this is relevant. For a given wheel, even after the curve turns upward, the drag is lower than it was at 0 yaw (except for the two cases), and comparing wheels, in general, the one with lower drag on the down side of the U, continues to have lower drag on the up-side.

I don't understand in what way a wind tunnel is not the real world. How is the air different inside a wind tunnel than outside? I think what you mean is that out in the field, we don't have as precise an understanding of the conditions in the tunnel. That doesn't mean that for the same conditions, the tunnel doesn't replicate the field test.

The wind tunnel doesn't do any scenario; it provides the parameters to put into a performance model such as here, https://www.recumbents.com/WISIL/Mart...%20cycling.pdf which is what is implemented in analyticcycling. It is up to the analyst to then perform the simulations using these parameters for whatever scenarios they see fit. The result will depend on the level of detail the analyst chooses to build in including whether or not parameter sensitivity and uncertainty quantification are considered.

justinzane

You note one of the consistent issues with human perception and numerical measurements -- we tend to suck at them without careful training and good instruments!

One of the ways I gauged the gusts was by the size and density of the crap that the gusts threw up. This was a pea-gravel knocked off the tops of ridges, large chunks of bark/mulch flying around, 1-2" dead branches coming off trees, cows all standing away from the wind kinda front. When I'm home, I've got an anemometer that provides real data to balance my perception.

I'd love to have an pair of onboard anemometers to actually measure airspeed while riding and I've got the Raspberry Pi to monitor them. I've just been lacking the motivation to find some small airflow/barometric sensors and create a bike friendly rigging for them.

justinzane

Makes it even more depressing... I'm 210-215lbs at 6'3", not a light rider, and I still had a brutal time.

justinzane

At least for me, I'm thinking the same is probably true as long as I live in high-wind geography. Wish I could find some published data on the subject to see if there was some rational basis for my feeling on the subject.

wphamilton

I'm not - I'm focusing on the scaling of the x-axis, and the context that there is basically no yaw angle over 17°.

Regarding the scaling, look at this from the article "the Zipp 808 are the surprise ...the first spoke wheels to achieve negative resistance ... from 13 to 22 degrees" . Doesn't it follow that other spoke aero rims did not achieve this? That comforms with my prior knowledge of the sweet spot up to around 12 degrees - I didn't know that the Zipp performed better than that. Kudos to Zip, but that doesn't change the performance of the other spoke aero wheels.


Basically it is straight, and non-fluctuating. Depending on how sophisticated the test is, it may not take into account vibrations, shifting of the wheel, movement of the bike as the rider shifts balance. The wind tunnel provides mostly steady state wind at different angles, but wind actually shifts frequently and gusts, with effects that aren't necessarily the same as a continuous transition from one steady state to another. The wind tunnel data is valuable and precise, but it is also for idealized conditions.

justinzane

I'm thinking that one way to test would be to do the wind tunnel tests like normal, but make sure to record, analyze and publish results with the wind at 0,15,30,45,60,90,120,135,150,180 degrees to the bike's "straight ahead". Preferable with rider wearing helmet, jersey with gels in pocket, as one would be in an actual ride. I would have thought that pro tour teams would pay for that since they compete in the real world. OEMs might not want it published, but it seems odd that those with an actual performance motive would not check.

justinzane

This is NOT actually true. Since drag increases polynomially with speed, but gravitation force increases only linearly with mass; a light bike will roll downhill at almost the same speed as a heavy one (assuming a difference in bike+rider mass of a few kg). On a steep hill, the drag down will be the limiting factor unless there is a crazy fast tailwind. On the upward track on the same hill, drag will be minimal but gravitational force -- the conversion of glucose chemical energy to gravitational potential energy -- will be far more important than drag in most conditions.

therhodeo

That post didn't dignify a response like this.

Stucky

Only because the differences are so minimal when talking about a pound or two, that it just doesn't matter.

It's a freaking bicycle! Just ride the damn thing and enjoy it!

Stucky

True. But really, why should we even care? Or even the racers, for that matter. So one bike is a few seconds faster than another....before long, they'll all have the same technology, so any advantage will be gone. But for recreational riders like myself, who cares? I always expected aero wheels to be sensitive to crosswinds. Now I have 35mm aero wheels...and sure enough...they are. I can only imagine 60mm's!

I just ride my bike and enjoy it. I'm not seeing a lot of joy in most of threads on these forums- despite so many people spending thousands of dollars on bikes- except for the newbies- until even they get corrupted by this all this BS from other cyclists.

justinzane

I actually think that the fact that some rims do convert sidewind to directly front (or rear) directed force IS relevant. If those rims do not generate twisting moment from 15-345 deg. and 175-195 deg. that implies that for 60 deg. (16.7%) of possible wind angles, stability is not adversely impacted and may be better than old-school rims. There is a further implication that some airfoil shapes on frames may also mitigate sidewinds in a small range around 0/180 degrees. That likely would enhance stability in that range.

I'd be curious to know, however, what side forces are generated on the steerer and on the whole bike+rider virtual object once one gets winds outside the "safe sixty" degrees quoted. And, do those side forces act closer to the center of mass of the combined bike+rider with aero frames/rims or further down? That difference, if it exists, in the height of the sideforce vector strongly influences the effective lever arm of the sidewind and therefore the stability of the system.

My guess is that if one were riding a philosophical bike with the same geometry as a Spec. Shiv that had 1mm diameter unobtanium tubes; the side force would be almost totally generated by the sidewind against the rider and therefore very slightly above the center of mass. On the other hand, a fictional planar rider -- think cardboard cutout -- with the same mass as a real rider on an actual Shiv with carbon disc wheel on back would experience a side force vector just above the chainstays and well below the center of gravity. That, I'm guessing would feel a lot wobblier, even if the forces were equivalent in magnitude.

Ok, I'm more interested in pizza at the moment than in thinking about force vectors. I'll stop polluting the interwebs for the moment.

wphamilton

The bolded portion does not follow, because you still have a side force against the wheel.

Stucky

And a larger area on the wheel, exposed to the wind.

justinzane

First, let me say that if I could reasonable build or buy a wind tunnel to have at home, I'd be there in a heartbeat. I'm a data geek, and that would be an awesome toy. I'd actually do thing like determining just what forces a birdhouse attachment fixture needs to survive on one of my trees. Oh, and of course, experiment with every conceivable bike, water bottle, clothing, facial hair fashion, etc. So, I'm not at all dismissive of windtunnel data or its use in extrapolative analytics.

But, riding on the road in wind, there are so many factors that mess with airflow that it is hard to imagine any reasonable set -- on something less than NASA or CERN's budget -- of tests that can provide enough disparate data points to allow reasonable thorough analysis. Where I ride is a very rural area, so the roads are much like the paved sections of the cobbled classics in the sense that they are relatively narrow and run through active farms, grazing fields and tiny towns. It is possible to transition from being on flat pavement next to a 1m high, 3m long downslope into a flat field to passing a relatively windproof 2m high x 10 m long hedge to being next to the equivalent upslope. Even with a constant 20km/hr wind at a 40 deg angle to a straight road, the differences in the terrain change the direction, 0-1.5m turbulence and so on of the wind one experiences within say 30m. At 30km/hr that is approximately 3.6 seconds to experience 3 different wind regimes.

Add to that the impacts of 50mph cars and trucks either windward or leeward, the gusty nature of most of the wind in some places, etc. All that means that it is hard to generate data that captures high frequency changes in wind speed and turbulence with typical tunnels. The ability to rapidly accelerate and decelerate the fans driving the tunnel, the ability to quickly and repeatable generate useful size and placed eddys, etc. seems to require quite an investment in tunnel hardware and I'm unaware that such exists in a way accessible to bike reviewers, manuracturers or teams.

My original question relates to how much effort is expended staying on the proverbial straight an narrow with the hypothetical bikes when passing into and out of said hedge or being passed by an 18-wheeler full of hay or... I know that the question is NOT answerable fully and accurately. But, I'm hoping that some testing has been done that is more useful to approximating the real world than simply testing straight into a constant laminar flow. I'd love to see data on the effect of eddies like those generated by passing vehicles on aero and non-aero frames/rims/bikes. I'd love to see simple 0, 45, 90, 135, 180 degree results with simple constant laminar airflow.

justinzane

Sorry.

justinzane

The reason I care is that I don't got the cash to be buying several nice frames and a few sets of rims and ... whatever. I'd like to get a well fitted, comfortable bike that will be the best compromise for the range of riding I do. Since I'm a novice and I had the wacky windy ride, I was inspired to think about some of the potential drawbacks to the drool-worthy aero bikes I see. I'm pretty sure that I feel most comfy in the steep seatpost, slack and low headtube geometry. I'm not at all sure that for someone as slow as I that the "aeroness" has much value beyond prettiness. And, if it has drawbacks that might matter to me but do not to someone trying to win an Ironman, I'd like to think that through in advance.

Oh, and I think that thinking about bike science is almost as much fun as riding. And, especially in crappy weather, more fun!

But, I quite agree with your core assertion that wankery analysis should never get in the way of getting in the saddle and pedalling off!

StanSeven

There is data from what I've read but it's not all that meaningful for a variety of reasons. What is more relevant is pro riders personal preferences. The old Sharp Garmin team is a perfect example. Riders could chose between the very aero S5, middle of the road S3, or the more traditional and lighter R3/R5. Some stuck with just one model while most switched based on conditions. The most common choice for all conditions is the S3, which is moderately aero yet much more comfortable and not so stiff that the rear wheel doesn't bounce cornering on rough roads.

More tour legs are in the 150 km range with pack riding so riders pick what gives them the best chance of doing well.

therhodeo

Nothing to be sorry about. Just don't think facts are going to make a difference.

wphamilton

Event the truly fast riders - pros - will choose the bike depending on course conditions, sometimes the non-aero bike but that's really only part of it. The geometry, how it rides.

For the rest of us, the aero shape of the frames poses no drawback at all, as an isolated quality. And only a small performance gain, measurable in the high end but in general less noticeable. But the frames are designed for other characteristics, that we can't really tell just from looking, and varies from one to the other.

Wheel selection has a greater impact on aerodynamics than the shape of the frame tubes, and greater impact on handling in more varied conditions.

justinzane

Here's a tidbit from Enve:



Annoyingly, they only publish 0-15 degrees!

-----
https://janheine.wordpress.com/2012/...orld-bicycles/ is thoroughly on topic, but the results were published in Bicycle Quarterly Vol. 6, No. 1 and Vol. 6, No. 3. It seems to be subscription, though. Anyone able to excerpt segments would be appreciated!

asgelle

And yet they were able to do this https://www.recumbents.com/WISIL/Mart...%20cycling.pdf and testing protocols have improved dramatically in the last 15 years; witness what Robert Chung has been able to do with virtual elevation.

Changing road or wind conditions just means the model has to have spatially or temporally changing parameters. There's nothing that precludes the analyst from including that level of detail if it's considered relevant. As to changes in wind speed and direction, these are still slow enough that a quasi-steady treatment is more than adequate.

asgelle

Or not. Road to Roubaix, Part 1 | SILCA Road to Roubaix Part 2: Tires (and Pressures) Are EVERYTHING | SILCA Road to Roubaix Part 3: We Just Invented the Future | SILCA

Pro riders are pros because they can peddle a bike really fast, not because they're really good engineers.

Stucky

That sounds like it could have been written by me! That's basically why I bought my Venge- comfort and position. I wasn't expecting it's aero properties to do anything for me [and I've had plenty of opportunity to test it out, as it's usually windy here.] and I was right....no difference between it and my non-aero Klein. In-fact, it is my contention that old-school bikes with skinny tubes and non-aero wheels probably do slightly better in windy conditions....less surface area exposed to the wind trumps aero shapes and more surface area- or so it seems to me. But, anywho, I did get what I wanted, in buying the Venge...a very comfy bike [a lot of people would disagree with me on that!] which stands out amongst many of the cookie-cutter one sees today.

Yeah, maybe it would save 1 second per mile- but if I were the kind of person who counted seconds, I'd quit cycling and become a UPS driver.

Hehe, yeah, I guess I find it somewhat interesting too- or I wouldn't get sucked into threads like these! I just take most of the analysis with a grain of salt, and cheer when I see a few others who realize that most of the "research" is either BS. or of little actual meaning to the average cyclist.

redfooj

check many of these
Aeroweenie.com - Aero Data Compendium

theyre tested at various AOA / yaw