Trakhak

Or your could choose to ride the lighter bike for the same elapsed time by taking a longer route.

CargoDane

60 kph is 37 mph. For comparison, When I hit 45 kph (downhill) I can really feel the wind. At 55 kph I spin out with my gearing (I am trying to become better at spinning).
In actual wind, I do try push through between the gusts.

On flat ground, I can hit around 40-45 kph before wishing for a heavier gear (not that good at high rpm spinning yet - I'm a natural masher), but truth be told, I'm not sure I could push the bike much faster on flat ground in a much heavier gear (at least this particular bike).

If you double your speed, you quadruple the wind resistance (force).
So, going 9 mph to 18 mph results in four times the resistance, and going from 18 mph to 36mph is four times that - which means that 36mph has 16 times the wind resistance as 9 mph. Yes, I did choose 9 mph because it came close to 37mph when multiplied by four, lol.

This is the reason for those time trial setups and why no one but Cubewheels stand up in strong headwinds.

60 kph/37mph is a Beaufort 7 - a "near gale". Something you most likely have experienced quite a few times, as most of us on here have (because it's not a rare wind strength).

Edited to add:
If going 20 kph (12.5 mph) into a 60kph/37mph headwind, the effective wind is 50 mph. That's almost highway speeds. There's an immense wind resistance at those wind speeds.

livedarklions

Like I said above, I am not defending his wind physics because I don't believe they're correct, just explaining how I deal with high headwinds in a manner that mitigates the aero effects. I'm not disagreeing with your math, I'm saying that people who are riding in such winds aren't really making progress except between gusts or when they can aim the bike out of the direct blast. Remember that a strong headwind can also be one hell of a great tailwind, and there's a lot of on-between impacts depending on where it's hitting you.

You and I aren't really disagreeing at all.

CargoDane

Oh! No, no, I wasn't thinking we disagreed. I was just trying to explain

livedarklions

Nope, if you want to get into an argument with me, you'll have to assert that a skin suit gives you major aero benefits at 15 mph. I forget how many pages were wasted on that one.

CargoDane

Haha, what? I hadn't read that. That is a glorious assertion!

CargoDane

No it doesn't. You have completely misinterpreted/miscalculated that. The only difference is rolling resistance. You will have more when you're actually going 80 kph rather than 20 kph.

The main force we are worried are the wind force. So it's the effective velocity of the wind. Not the velocity of the bike as the only thing thing that has an influence here on the actual bike is the rolling resistance. To find the wind resistance, all you need to concern yourself with is the effective wind velocity.

ofajen

That link doesn’t work for me, but the result is correct.

The air drag component of cycling work is k(a)*A*v**2*s, where s is the bicycle speed on the road, k(a) is the air resistance coefficient, A is the combined frontal area of cyclist and bicycle, and v is the bicycle speed through the air (i.e. road speed plus head wind speed).

So, the v**2 term is the same and the difference is the value of s: 20 vs 80.

Otto

CargoDane

Again: That would be true if we weren't talking about wind, but merely talking about wind resistance in still air.

To calculate the force of wind resistance, you cannot ignore actual wind speed in relation to the ground (and you). If you could, it would be equally hard to ride 20 kph in still air, in 60 kph headwinds, and in 60 kph tail winds as there is no effective wind resistance at all other than what results from your own progress over the ground.

Wind resistance (drag) is calculated against the speed of the wind, not the speed over ground. Hence why planes go slower over the ground in a headwind, and faster with a tail wind, yet they travel through the air at the same speed.
This is also the reason that wind tunnels work. If you calculated drag as speed over ground, wind tunnels would be absolutely useless.

To put it another way: Wind resistance (drag) is a measure of how much resistance there is for going through the air at a given speed.

preventec47

I bet we could probably learn a lot about heavy bikes from those guys who drive bicycle taxis in various parts of the world. I am no specially skilled rider
but I have a tandem bike and I give rides to a number of people who are otherwise unable to peddle. i have a place in the frame where I ask them to
keep their feet so as to not interfere with the cranks going round and round. Hard to put into words but you do indeed gain a unique perspective.
I also ride my tandem solo which is unique.... I say it feels like a bicycle limousine. One thing I have to say i like a little bit is the fact that the front wheel steering is far less twitchy and might be more steady if I was riding hands off .... which I would never do.

locolobo13 

My bike isn't light. Nor heavy. By the time I load her up she feels heavy. A lighter bike would be faster. But she takes me where I want to go, mostly. You just have to figure out what you want.

This thread reminded me of an episode of "Insider Training" with Laird Hamilton. They showed him and somebody else loading up mountain bikes with weightlifting plates and riding dirt and gravel for the extra exercise. That looked heavy.

livedarklions

During WWII, the original mission for the B-29 bomber was high level bombing of Japan. However, it turns out that the jet stream flows directly over Japan at that altitude, so that the bombers were attempting to fly directly INTO the jet stream while dropping their load. The planes were often going about 5 mph in reverse while still maintaining lift. Needless to say, it was absolutely impossible to control where the bombs landed under those conditions, and the planes started flying their missions at a much lower altitude.

preventec47

A commonly known constant in aviation is that the aerodynamic drag increases by the cube of the speed. ie 20mph requires eight ( 8 ) times the
power to overcome the drag at 10 mph. 40 mph requires (64) times the power as 10 mph. For ground vehicles add in some for rolling resistance.

CargoDane

Yes, becaise you're both doing it wrong. Wind resistance is drag through the air, not speed over ground. The only place the two are the same if there is no wind whatsoever.

Ever notice that it is easier to ride fast with a tail wind than it is with a headwind? The reason for that is that your speed through the air changes, and therefore the drag.

CargoDane

You're right, I actually miscalculated the drag factor quite a bit.

Trakhak

Or, more logically, do what I said.

squirtdad

imho wrong in so many ways..... mostly heavy bikes are cheaper with cheaper components requiring more repair. Heavy does not mean rugged, it just means heavy, often because of cheap components, heavy tubing ,etc.
riding a bike should be a joy, I don't get joy out of riding something heavy and ill suited for the riding your are doing.

Life is too short to not to ride your best lightest bike as much as you can

ofajen

As noted in the equation I gave, drag (the product of k, A and v**2) is proportional to the square of relative wind-speed, v, while power is the product of the inline portion of that drag and rider speed, s. Required power only increases as the cube of speed in still air.

Otto

CargoDane

Relative windspeed.

And you're wrong when you say "Required power only increases as the cube of speed in still air.". No, that is only the point where the ground speed matches the speed through the air. I can't believe I have to say this again: Your wind resistance is the resistance you meet by going through the air. It doesn't matter if it's you who is moving at hurricane speeds or it's the wind moving at hurricane speeds in relation to the ground.
Seriously, planes would have really weird stalling limits, you wouldn't be able to tell the difference on a bike with headwinds or tailwinds, nor would wind tunnels work at all.

In a headwind, your speed through the air increases even though your ground speed doesn't. You said he was "correct" in his calculation, but he is only right with his calculation if there is no wind. Required power to move through the air doesn't change due to your ground speed. It changes the same whether the air is moving faster or you are moving faster through it. Again: Notice a difference while riding 25 mph in a headwind vs. a tailwind? Force required in the headwind will be higher than in still air, and much higher than with the tailwind.

CargoDane

1) No they don't. Not unless you guys can cheat physics (and the formulas)
2) Yes, in still air.
3) You two should know better by now as it has been explained ad nauseam to you.
4) If the formulas held true that ground speed is the same as wind speed - even with wind around, you wouldn't be able to tell a difference with your bike between going in still air, in tailwinds, or in headwinds - even at hurricane force winds.

And, finally:
5) It has reached a point where I'm beginning to suspect you're doing this on purpose, that you're actively pretending to not understand things in order to troll. No one can continue to stay, let's call it "that unknowing" unless it's on purpose.

tomato coupe

Actually, he's correct about this. When riding against a headwind, the power required to overcome aerodynamic drag scales like the square of (ground speed + wind speed) multiplied by ground speed. In other words, it's proportional to the square of the air speed multiplied by ground speed. In the absence of wind, the equations reduce to a simpler form, and the power scales with the cube of ground speed.

With airplanes, the power required to overcome aerodynamic drag simply scales with the cube of air speed.

CargoDane

That's wrong too and not what he is saying. You don't multiply your ground speed with the air speed. The wind resistance (air drag) is solely a function of how fast you go through the air. Full stop. And the only time ground speed and air speed can be interchanged is when there is no air movement whatsoever.

Again, you're wrong. Go do some calculations for me to check. Other than rolling resistance, it doesn't matter if the wind is moving or you are moving. Again: Frigging windtunnels, headwinds, and tailwinds.


LOL, even with that knowledge, you still argue that aerodynamic drag in the air is somehow different than aerodynamic drag if some part is touching the ground (by many, many factors since you want the aerodynamic drag to be multiplied with the ground speed).

In other words, you're arguing that lift and drag forces changes - as well as stalling speeds) for the wings AND propeller/s if the wheels are touching the ground vs. not touching the ground. Let's hope they're not dragging a piece of string on the ground, because suddenly they have to deal with forces multiplied by the ground speed.

tomato coupe

That's correct. The aerodynamic drag depends on the square of airspeed. But, the power required to overcome the aerodynamic drag depends on the aerodynamic drag multiplied by the ground speed of the bicycle.

I have done the calculations, and it does matter. Riding at 20 kph into a 20 kph headwind is not equivalent to riding at 40 kph in still air.

No, it isn't different just because "some part is touching the ground." It's different because the part touching the ground, i.e. the rear wheel, is the means of implementing the forces that overcome aerodynamic drag.

The power required to overcome the aerodynamic drag in an airplane scales as the cube of airspeed. Dragging a string does not change that. Wheels on the ground only changes the calculations via rolling resistance or braking forces.

You can check any number of references or textbooks; they will not support your argument.

CargoDane

No, you haven't done the calculations. Of course you won't get the same results is you afterwards multiply the speed through the air with the ground speed. Seriously, I'm done with lies.

Especially the part where you argue the drag changes because wheels are the propulsion rather than, say, gravity or a propeller. If dragged changed due to whether the propulsion is in the air, on the ground or in the water for that matter.
So, in other words, drag will change immensely the moment you stop pedaling, the moment you jump over something, or the moment you let gravity take over.
It's air drag. It's a force to do with air. It doesn't matter if the vehicle in question is standing still and the wind moves, or the vehicle moves and the wind doesn't (or both). It's the movement through the air, and with boats, although those also have air drag, it's mostly about drag in the water. It doesn't matter if the propulsion are sails or a propeller.

Show me those "reference books" which supports your claim that it matters what actually propels you. Those same books would also say that drag cannot be calculated in wind tunnels and that headwind and tailwind produces much less drag when you use, say, a tow rope rather than the wheels, or a rocket engine rather than wheels.

You're not even sure about what the consequences of what you're saying have. WHY would what type of propulsion used to push against the force of the effective wind matter. No, I don't need another unsubstantiated claim. I am asking why. Any propulsion system produces a force to counteract other forces to move.
If what you said were true, then the moment one starting applying force while riding (let's say downhill, but could be anything), THEN suddenly the forces to overcome are somehow suddenly multiplied.

The opposite is also true: If you pedalled yourself up to speed downhill and then suddenly stopped pedalling, then suddenly the drag you're trying to overcome would then be divided by your ground speed, meaning you would actually accelerate as the forces you are trying to overcome are suddenly decimated.

No frigging textbooks supports any such claims.

Another thing I want you to explain according to your "understanding" of this: How does tailwinds and headwinds work? How does wind tunnels? This is beyond ridiculous.

tomato coupe

Here you go, just substitute bicycle for car: