grwoolf

Assuming I have a perfect 90 degree (running exactly perpendicular to my direction of travel), does the crosswind affect my speed vs. a wind-less day, how much, and why (assuming a solo rider)?

In general, I'd think a cross wind would not have much affect because the force is pushing from the side, but I assume there is more to it than that (based on how much they seem to slow me down).

I'm guessing that a cross wind probably disrupts the smooth flow of air around the bike/rider (compared to a windless day), creating more resistance.

I was also wondering if the rider has to use some small amount of energy to 'lean into' the wind while riding or if this is just a balance thing. I know on a really windy day, I feel like I'm constantly fighting with the bike (particularly in a cross wind).

Sorry if this a stupid question, but this is the kind of stuff that gets in my head while riding.

cyclezealot

While out on a ride, I've had sudden weather changes, creating cross winds of 50 MPH or more.. This area is known for it's winds... I'd say when I slow down in order to lessen the chance of being blown over, i'd say my speed has been affected... . But, the odd thing, as often as I sense cross winds , I also feel head winds.. That can be as great a work out as ascending a steep grade..

Velo Dog

Bicycling magazine (I think--may have been Cycle Guide, which is no longer around) did a story on this 15 or 20 years ago, with wind tunnel tests. I can't remember the details, but the conclusion was that wind in a 270-degree arc from straight ahead hurt performance overall--that is, unless it was coming from within 45 degrees to either side of straight back, it slowed you down. Didn't make a lot of sense to me then, and it doesn't now, but they seemed convinced.
As for energy fighting a crosswind, of course it takes some. Just man up and ride. Or stay home, which is what I'm probably going to do this afternoon.

Bianchigirll 

I think I read the same article! I totally agree. why wouldn't a cross wind slow you down? the air is disturbed before you you 'break' it and therefore rougher than if there was no movement in the air. this is just like riding in a paceline. it is easier to stay 2" from a wheel then 1' behind it and you can keep pace abreast of a rider than if your were a few feet behind.

I understood this after I started working for a air freight service and started to learn a bit more about aero dynamics

banerjek

I remember that article (though the one I'm thinking of was published more than 25 years ago). I agreed with it then, and I still do though your posture and equipment have a significant effect on how much wind resistance you get at different angles.

Crosswinds have a huge effect because it totally changes the airflow around the bike and the rider. To make things worse, winds typically vary because they change on their own and features in the landscape create currents and eddies. When winds slow you down and then drop, the practical effect is you wind up wasting a lot more energy accelerating even if you maintain constant power.

As if that knowledge should ever affect your decision to ride. HTFU.

asgelle

Aero drag doesn't depend on the the true wind over the ground but the apparent wind on bike and rider, i.e., the vector sum of the true wind and the bike velocity . If a rider is moving forward at 15 mph and there is a side wind at exactly 90 degreed also at 15 mph, the apparent wind is at 45 degrees at a speed of 21 mph. Virtually every riding condition results in an apparent wind from the front.

Grumpy McTrumpy

https://www.hedcycling.com/aerodynami...calculator.asp

ejbarnes

I read the same article in the last year or so.
The 270° idea is that you are leaning into the wind, more or less steering into the wind.
Therefore you will be affected by the wind.
I notice much more work in side wind when using a wheel with a deep rim but the hill climb rims can also make for a twitchy ride on a very windy day.

Heck I even notice much more work when running with a side wind.

asgelle

You realize that flies in the face of all the recorded data - wind tunnel, field test, analysis?

ejbarnes

Try it. A good wind gust can almost blow the wheels out from under you.
I think the aero factor works in the forward direction not sideways, as from the side it creates more surface area.
Like a fat person and a skinny person.

BarracksSi

Yup. The only way you won't have an apparent headwind is if it's coming from behind and if it's blowing faster than you're riding.

achoo

Not only those effects.

A wind from the side introduces a significant side force on the bike and rider. The only place that side force can be offset is where the wheels contact the ground. I'm not sure of the exact physics going on, but your rolling resistance goes up because of that side force.

I actually did some experimenting when I was out in LA and did a lot of biking on the coast between PV peninsula and Santa Monica, where crosswinds are pretty much the norm. I once tested how far I'd coast on a flat stretch one morning when there was no wind. A couple of days later I passed the same spot with probably a 10-15 MPH crosswind. My rough experimentation had me rolling only about half as far as I rolled with no wind.

exRunner

I am going to simplify the math somewhat, but basically: If you do a vector force analysis you will discover that the side force that the rider is feeling has to be countered in some manner or the rider is going to be knocked over. That is done by the rider and bike leaning into the wind. The force is now balanced in such a manner that it is transferred to the ground. In effect, you and the bike get heavier.

It might seem counter-intuitive at first glance. Now, how much force and how much effect is questionable and nearly impossible to calculate, but I would guess it is pretty small in the big scheme of things.

umd

You are still moving forward into the wind. Less so that if it was a pure headwind, but there is still a forward component to the vectors when added together.

ricohman

Cross winds are killer.
I live in the land of never ending wind.

asgelle

This is physics, not what color should your bar tape be. It isn't a matter of opinion. While frontal area increases with increasing yaw, the drag coefficient decreases faster than area increases. As to the "aero factor" working in the forward not sideways direction, drag is a vector quantity and exerts a force parallel to the direction of the flow. Of course, there is also a force normal to that; we call it lift.

Anyway this guy comes home and sees his wife in bed with his best friend ...

achoo

So, that's another impact of crosswinds.

Do the force vectors on the tire contact patches. If the wind is pushing the rider to the left, there must be an equal force on the contact patches pushing the rider to the right. And that is going to be in addition to the lean you mention - that lean is there to counteract the torque from the two side forces of the wind and its countering force on the contact patch.

I'm thinking that that in addition to the changes in aerodynamics mention earlier along with the lean you bring up, the side force on the contact patch does something to directly increase the rollng resistance of the wheel and tire. Maybe the torque on the wheel bearings makes them roll less efficiently, maybe the tire doesn't roll straight ahead and has to crab like a plane in a strong crosswind, maybe the tire is actually skidding sideways just a bit. Maybe all of those.

bbattle

I was watching a video of the Coors Classic races back in the 80's. They had full disc front wheels. Wonder why they don't do that anymore?

asgelle

I didn't realize 1080 mm deep rims were available in the 80's. Do you have a picture of them?

BarracksSi

According to Sheldon Brown, there were disc wheels back in the 1800's:
https://www.sheldonbrown.com/gloss_da-o.html

bbattle

Francesco Moser

neuronal

What the hell are you talking about? You make it sound as if there's a non-trivial number of wind tunnel tests that compare wind flow from different directions on bicycle wheels. Link me to 3.

asgelle

What am I talking about? At this point testing over the full range of relevant yaw angles is so routine that a masters racer trying to improve his position does it as a matter of course https://www.cyclingtechblog.com/2009/...b-at-texas-am/. Further, anyone testing only at 0 yaw would have their results laughed off the stage (see MIT cycling team).

But anyway, here's a bunch. https://www.zipp.com/_media/pdfs/technology/rimshape.pdf

neuronal

Nice job...first link doesn't even compare wheels, second link is from Zipp and doesn't substantiate any of your claims seeing as how they only test at 30 degrees max.

neuronal

If you're gonna dispute someone's claim (i.e. this guy's), link to relevant stuff. Try again. And don't quote people out of context as you did above.