How much does wind slow a bike?

[tommaguzzi]

Still. 20 mph for 3 hours is some going in a loop where there cannot be wind assistance all the way.
I once tried a one hour tt on British Cycling's closed racing circuit at Middlesbrough.
There was a slight headwind on the very small up gradient on the back straight and quite a few turns which would slow me down. I did 19.8 miles I seem to remember. Just short. I was 10 years younger and a fair bit quicker than I am now and I was tired at the end. No way could I have done another 2 hours at that rate.
While I dont doubt the OP if he can do 20 mph for 3 hours he should think about completing .

 

[johnnyb47]

I find the wind a big factor in my cycling. When I first got back into cycling a few years back i never really noticed it. I would put that down to being a slower cyclist back then and the lower speed = lower wind resistance. Now I'm a little faster i really feel the head winds more. Cycling hard with the wind behind gets some great speeds, but when you turn against it, the resistance of it trying to maintain a quick pace really slows you down. Recently I've slammed the stem on my bike and this has made a considerable difference. Riding on the drops in a head wind really helps battling against it. I would imagine commuter type bikes where you're positioned in a more sit up beg position, you would catch more of that head wind.. I've become quite obsessed in looking for flags on my rides to determine which way the wind is blowing

 

[HLaB]

Still. 20 mph for 3 hours is some going in a loop where there cannot be wind assistance all the way.
I once tried a one hour tt on British Cycling's closed racing circuit at Middlesbrough.
There was a slight headwind on the very small up gradient on the back straight and quite a few turns which would slow me down. I did 19.8 miles I seem to remember. Just short. I was 10 years younger and a fair bit quicker than I am now and I was tired at the end. No way could I have done another 2 hours at that rate.
While I dont doubt the OP if he can do 20 mph for 3 hours he should think about completing .

If they are doing 20mph in undulating terrain definitely, if its in flatlands they'll still be fast and will have fun competing (I do) but don't expect to compete with the best guys. You'd be surprised what you can do/maintain in flat terrain speed wise

 

[SkipdiverJohn]

I reckon the difference in speed for the same physical effort when riding in wind ought to be the square root of the wind speed - assuming you are either directly facing or directly backing the wind direction.

 

[MntnMan62]

Head winds definitely slow me down. The stronger the winds, the more it slows me down.

 

[Blue Hills]

If you want to answer the question. Go to the fens on a typical day and ride north. Then turn round and come back south. You’ll soon see what effect the wind is having.

Shudder. Terrible memories of riding across the fens heading south west fully loaded for a peterborough train.

 

[Twilkes]

What is 'a fen'?

 

[matticus]

...

While I dont doubt the OP if he can do 20 mph for 3 hours he should think about completing .

We're now well off-topic, but I'd like to point out that TTs are for everyone (if they can ride 10miles non-stop, anyway!). It's you against the clock, no minimum speed. (bunch racing is a very different thing ... )

And meanwhile, fast people are allowed to ride just for fun!

 

[nickyboy]

lol - so have I, although 20yrs later probably couldn't find my arse with both hands regarding most of the subject matter now

Isn't force x time the formula for "impulse"? My understanding of mechanics gets sketchy once past the basics..



FWIW I'd say that the in real-work terms you'd probably expend more energy / require more power to complete the same ride in windy conditions, but more because of tertiary issues rather than the square drag law - which shouldn't make any difference as that relationship applies whether the wind is assisting or hampering you.

Where the effect of the drag law does become relevant is on hilly terrain since due to the high speeds (and associated exponentially growing drag) encountered on descents, proportionally less of the potential energy gained on the climb is translated back into speed on the descent, if you see what I mean. So, if seeking to maintain a high average speed throughout a hilly ride the best tactic is to expend as much energy as possible attacking the hardest ascents (where speeds and hence aero drag are lowest) and putting in zero energy on the descents while seeking to minimise your drag / frontal area.

You need to do the maths regarding the square drag law. You'll find this is the main reason why average speeds are lower on windy rather than still days. I did a very simple calculation upthread to show why this is the case

Imagine a cyclist who is programmed to produce 150W all the time, regardless of conditions. You'll find his average speed on a windy out and back ride is lower than on a still ride

 

[NickWi]

Apologies to Nickyboy but to change his wording just a little. "Imagine a bicycle that is programmed to produce 250W all the time, regardless of conditions."

Buy an ebile, whack it on full power, problem solved!

 

[CXRAndy]

While I dont doubt the OP if he can do 20 mph for 3 hours he should think about completing

Id never cycled faster than 20mph in a club run. I entered the Tour of Cambridge and at 53 years old averaged 21.3 mph for 80 miles. I wasn't by any means the fastest. Some of my mates average 23-24mph

 

[Ming the Merciless]

Indeed on the flat, on my recumbent, I can comfortably maintain 27 mph. If I had a velomobile I’d be comfortably north of 30 mph. I’m no racer, it’s just the aerodynamics significantly reducing the power required.

 

[SkipdiverJohn]

it’s just the aerodynamics significantly reducing the power required.

Predominately aerodynamics, yes, but not entirely. Weight and drag still matter. Last Saturday I did a route on my old Raleigh 3-speed and noted the elapsed time (as it doesn't have a Cateye computer fitted), and yesterday I repeated exactly the same route riding a Raleigh MTB on knobbly tyres with a computer. The distance on the MTB was 19.5 miles and the average speed was 10.7 mph. On the roadster, the elapsed time by stopwatch was a minute less, so the average speed was marginally higher. Both very non-aero, especially the 3-speed. Flat bars set high for comfort. MTB weighs 32 lbs, roadster weighs 41 lbs but even so was still a tiny bit faster. Clearly the knobbly tyre drag not only outweighed the MTB's weight advantage, but also the fact that it was marginally more aerodynamic.

 

[Ming the Merciless]

Predominately aerodynamics, yes, but not entirely. Weight and drag still matter. Last Saturday I did a route on my old Raleigh 3-speed and noted the elapsed time (as it doesn't have a Cateye computer fitted), and yesterday I repeated exactly the same route riding a Raleigh MTB on knobbly tyres with a computer. The distance on the MTB was 19.5 miles and the average speed was 10.7 mph. On the roadster, the elapsed time by stopwatch was a minute less, so the average speed was marginally higher. Both very non-aero, especially the 3-speed. Flat bars set high for comfort. MTB weighs 32 lbs, roadster weighs 41 lbs but even so was still a tiny bit faster. Clearly the knobbly tyre drag not only outweighed the MTB's weight advantage, but also the fact that it was marginally more aerodynamic.

Weight doesn’t matter it’s flat and drag is included within aerodynamics.

 

[SkipdiverJohn]

Weight doesn’t matter it’s flat and drag is included within aerodynamics.

Weight matters as far as acceleration goes, and in urban riding you have to use the brakes more, which turns momentum into heat. So you invest more energy in getting the mass up to speed but can't utilise all of the momentum created because of the need to brake. If weight didn't matter at all, no-one would care if racing bikes were heavy as they would be just as fast as light ones. Frictional drag from tyres and mechanicals is separate from aerodynamic losses.