How much does wind slow a bike?

[davidphilips]

Know that cycling into a say 20mph wind will slow down a bike by about 10mph but does cycling in a windy day slow you down much? know it slows me down and i dont seem to be able to maintain any where near a good average speed on any loop? Example on a good day i can cycle one 60 mile loop in just over 3 hours this morning it took me over 3 hours and 40 minutes and i was really pushing as hard as i could (windy this morning) ?
I never seem to be able to gain as much from a tail wind as i loose from a head wind?

 

[DSK]

Its certainly been more windy over the last week or so. I can't recall how much it typically slows me down but, as soon as its enough to be noticeable it annoys me and I find myself giving it everything to try and maintain pace, especially with cars on my @ss. I find it easier to make myself more aero rather than try and power through it as the latter is hard work and doesn't really do much.

 

[T.M.H.N.E.T]

A tailwind is a phenomenon in these parts, if it's particularly windy I prefer to hide on hillier routes where the wind is generally less of a factor and average speed is going to be lower for that ride anyway.

 

[Drago]

I find that wind speeds me up. A diet of beans, duck eggs and Pernod used to shave 5 minutes off my daily commute.

 

[davidphilips]

Lol Drago never though of that, what i can not understand if going into a head wind i get more aero yet still can not make up speed/time lost when theres a tail wind?

 

[Brads]

I'm struggling with this one as I have spent years bitching about the wind slowing down my average pace.
For reasons unknown to me, I am hitting faster speeds this year even in very windy conditions.
I'm older and have been MTBing all summer only hitting the road bike in the last 2 months but am quicker than before.

Very windy last week and a car driver and his missus clapped and waved as they passed me flying along the flat at near 60k/ph

 

[CanucksTraveller]

I am slower in windy conditions, personally I feel it's largely psychological. I kind of feel like it's a battle from the off, and I feel that little bit more defeated (or possibly defeatist) every time I head directly into the wind. I think that just saps my will and mentally knocks me back, translating into less than peak effort and a general "trudge" feel to proceedings. I reckon that feeling of being beaten lasts and hangs like a cloud, even over your "wind assisted" bits. Far from scientific I know, but it makes some sense to me. On a calm day I often fly along with some elation and adrenaline in my veins which I never really feel in the windy conditions.

 

[welsh dragon]

I was going to say ask Drago, but he beat me to it.

 

[Drago]

Being serious for a moment - which comes difficult for me - I don't think a tail wind speeds me up by the same degree that a head wind slows me down, but it certainly feels a lot blummen easier.

 

[nickyboy]

The stronger the wind, the slower your average speed. It's all about the physics.......

Wind resistance is proportionate to the SQUARE of the speed. So imagine you cycle 15 miles out, 15 miles back, at 15 miles an hour on a completely still day. That takes two hours, right? In that time you've suffered 15x15x 2 hours of wind resistance. That's 450 wind resistance units

Now imagine it's a headwind out of 5mph, and you only manage 10mph. That takes 1.5 hours. So to do the whole ride in 2 hours, you need to cycle back at 30mph. Your outbound wind resistance is 15x15x1.5 hours. Your inbound wind resistance is 25x25x0.5 hours. Total is 650 wind resistance units

Of course, you don't manage to deal with the big increase in total wind resistance...so you go slower overall

 

[Sharky]

Maths is not my strong point, but I think if you ride for an hour at 20mph with the wind and 10 mph for an hour into the wind, the average would be 15mph.

Unfortunately on the bike, it's not an even time split. You will spend 75% of the time into the wind and only 25% of the time with the wind, so not enough time to make up.

 

[Lozz360]

When it's windy plan your ride so you cycle into the wind on the way out, then you have the tail wind when you return and you're tired. You can also do a loop around a town so that the wind direction means that you are sheltered when riding into the wind and exposed when the wind is behind you.

 

[wafter]

Unless travelling extremely slowly air resistance is the dominant factor that controls our speed as cyclists.

Frictional losses, rolling resistance etc generally rise linearly with the change in road speed (so double the speed, double the losses / energy required to overcome them) while aero drag increases with square of the change in road speed (so double the speed, four times the drag / energy required to overcome it).

SImplified (negating the effect of moving wheels, ground effects etc), the influence of wind can be explained with the simple concept of superposition and relative air speed; therefore it takes as much power to maintain 10mph into 10mph headwind as it would to maintain 20mph in still conditions or 30mph with a 10mph tailwind.

In an ideal world a flat loop under wind of constant speed and direction should make no difference to your average speed as the amount of retardation and assistance cancel out.

 

[T.M.H.N.E.T]

Then winter happens and everyone is slower again

 

[Twilkes]

I once asked a windy question on stack exchange: https://bicycles.stackexchange.com/questions/65234/how-do-sidewinds-affect-forward-speed