asgelle

You might be interested in this https://forum.slowtwitch.com/Slowtwit...24mph_P2474619 and the interview with Josh Poertner referenced there https://nyvelocity.com/content/equipm...-josh-poertner

neuronal

Good reads. Quote from the article (from a ZIPP engineer no less): "It's very rare that you're going to have a most likely wind angle of 20 or higher, 'cause that means your peak wind angle is going to be 40 or more, and to get there you either have to be going really slow, or have really ridiculous wind speeds, at which point most people are going to opt for shallow wheels."

I would say that the rarity of the situation is not as extreme as he is allowed to claim in an interview, but there it is.

Grumpy McTrumpy

maybe you just don't go fast enough.

asgelle

Have you ever met or talked to Josh? Having had many exchanges with him, I believe him to be as honorable as any researcher I've ever met. For implying that he would distort the science to suit the marketing, I believe an apology is in order.

joejack951

No, that is not what is happening. Without the presence of a crosswind, a rider stays balanced by keeping their weight centered over the wheels. As keeping this centered point forever is impossible, bikes have steering to correct the position of the bike under the rider keeping them upright. Now, when you add in a side force (crosswind), the cyclist has to compensate for this. If you were able to determine the exact force applied to the rider by the crosswind, you could easily determine what angle the cyclist would need to lean into the wind at to stay balanced (you'd need to know the rider's center of gravity too). Leaning simply applies a counter-torque to the torque applied to the rider by the force of the wind. The system pivots about the tire contact point. The rider leans about their center of gravity. The wind applies a force to the rider centered on the bike/rider's centroid which is affected (both the force and centroid) by things like deep section wheels, aero frames, or panniers.

In my experience dealing 30+ mph crosswinds, the force can be very significant as noticed during gusts where a sudden change in wind direction can mean moving a few feet laterally on the road. It's quite normal to find the relatively heavy trash bins blown all over the street during the high wind days which demonstrates the amount of force the wind can apply to an object with a decent cross section.

neuronal

This thread is becoming silly. I'm sure that Zipp guy is great, but it doesn't change the fact that heavy crosswinds are not rare, depending on where you live. Who cares if I ride slow and average 16 mph during the winter? Doesn't change the fact that occasionally the 20mph winds here do create a high apparent wind angle. This entire argument is tangential to the original argument about whether or not deep rims reduce "work" in heavy crosswinds anyways.

asgelle

Nor does any of this change the fact that you impugned the honesty of someone you don't know. I guess in a couple of days we'll get the clarification of what you really meant.

In the meantime, as I said above, we have lengthy explanations by the leaders in the field of cycling aerodynamics explaining what yaw angles are reasonable, and then we have you saying in effect "I refuse to believe it."

neuronal

A few less personal attacks and a few more facts would greatly help your argument. Misquoting "leaders of the field" isn't going to make your argument more solid. As far as I can tell, none of these experts (even the guy at ZIPP) is denying that a shallow rim is preferable in heavy crosswinds. And certainly it's not the case that angles of >30 never happen. On almost every ride I've been on in the last month, there have been sections with gusts above 30 mph. If I were riding perpendicular to the wind in these situations, the apparent angle would be >30 degrees.

Like I said before, I'm not talking about 90% of riding conditions. ZIPP wheels are manufactured for efficiency in 90% of riding conditions. We are talking about heavy crosswinds. It almost sounds like you are denying that heavy crosswinds exist. Pretending that "leaders of the field" agree with you doesn't make it so.

asgelle

One simple question: How would you know?

(and now you're misusing efficiency.)

neuronal

Weather reports, mostly. But you can also feel heavy gusts. If we take your point that wind speed on the ground is slower than 5 meters above the ground into consideration, I suppose 20 mph is more realistic. Anyways, the point still stands. Keyword here is "gusts".

I was using the layman's definition of efficiency. You get the point.
Places near where I live: https://www.wunderground.com/weathers...p?ID=KMACAMBR9
https://www.wunderground.com/weathers...p?ID=KMAMEDFO7

asgelle

Keyword here is "suppose."

neuronal

Calculations based on this: https://en.wikipedia.org/wiki/Wind_gradient

It's reasonable to estimate that at 1 meter the wind speed is 70-90% of the wind at 3 meters off the ground. But even if it was 50%, the angle is still >30 degrees with 30mph gusts.

I can see that this conversation has basically run its course.

umd

Get a room you two.

Bah Humbug

Very direct yes-or-no question for you: do you believe wind speed on the ground ever hits 20mph?

asgelle

No.


Do you?


Do you believe in viscous flow?


Was this a serious question?

neuronal

Assuming a 40mph gust (measured at 10m off the ground), the wind at .5 meters about 20mph (if there aren't too many buildings or trees in the way).

asgelle

That's nice but why didn't you answer the question? Do you believe wind speed at the ground ever hits 20 mph; yes or no?

neuronal

Yes. On the ground isn't referring to 1cm above the ground- it usually means .5m to 1.5m from the ground.

Furthermore, "the ground", as Bah Humbug is probably talking about, refers to the anywhere that you can reasonably cycle. I'm pretty sure that if you ride up an exposed mountain pass or along the coast, winds can get pretty high on "the ground".

Jynx

on the ground definately does not mean 1.5 meters above it.

neuronal

We're talking about cycling here, not insect life. Defining "on the ground" as lower than .5m is pointless. 1.5 seemed reasonable to me, but .5-1m is the height most people care about.

asgelle

I'm not a mind reader. To me "on the ground" means "on the ground," 0 elevation. To someone studying non-continuum flows, 0.1 micron is way off the ground. To an astrophysicist, 10,000 m might well be considered on the ground. There's a really good word for distances slightly away from something else, it's called near. For example, "Do you believe the wind speed ever reaches 20 mph near the ground?" Though in the context of this discussion, it would be better to ask "Do you believe the wind speed ever reaches 20 mph 0.5-1 m above the ground?" None of those was the questions asked.

asgelle

Why do you think it's pointless? All viscous flow is based on the hypothesis of what happens "on the ground" To understand precisely what someone believes is the operating physics on the ground is crucial for understanding everything about their analysis of viscous flow. In other words, it's impossible to understand what happens at 1 m, if you don't understand how "on the ground" is treated.

Jynx

I understand your question. Unfortunately you can not assume everyone will know what you mean. Like asgelle said, on the ground means something totally different to different people studying different things. If you want to know if a cyclist ever experiences 20mph winds at their respective height, that is a different question.

neuronal

Once again, it seems like we aren't talking about the same thing.

I was talking about how wind speed affects wheel performance. Wheels are on average about .4m off the ground. Cyclists are on average 1-2 m from the ground.

If this were a engineering forum, I would have used more specific language. It was a mistake on my part to assume that you could gather from context that "on the ground" was not meant in the most literal sense of the phrase.

neuronal

I think, as someone stated earlier, we aren't actually disagreeing on anything besides definitions. Let's lay this thread to rest.