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Take your average 9 kg roadbike and 75 kg roadie on the hoods going at 40 km/h.
A 20 km/h headwind would bleed you around 300+ watts (1), but tailwinds giveth you less than headwinds taketh away so perhaps you'd need to put down 200w less power to stay at 40 km/h than with a 20 km/h tailwind compared to none?
I'm wondering since a lot of sTrAvA KOMs around here seems to be done in hurricanes and there's no power data, personally my goal is to improve my P..get all of them.
1. https://www.yellowjersey.co.uk/the-draft/how-much-difference-does-a-headwind-make-when-cycling/
Hmm I think the question isn't correctly formed.
Are you saying a cylist needs 700w to cycle into a 20km/h head wind at 40 km/h. Either you can produce 700w or you can't. No one can sustain that for long.
Are you asking how much power is needed to cycle 40km/h with a tail wind?
https://www.analyticcycling.com/
Have a play here.
Specifically here:
https://www.analyticcycling.com/DiffEqWindCourse_Page.html
I'm saying that a 20 km/h tailwind will make it 200w easier to stay at 40 km/h. So you could hold 40 km/h at around 250 watts I'd guesstimate.
https://www.analyticcycling.com/DiffEqWindCourse_Page.htmlhmm not getting watts saved out of it
Rolling resistance is small, and assuming you’re on the flat... Drag changes with the square of airspeed.
40k with a 20k headwind means 60k airflow over the rider.
40k with a 20k tailwind means 20k effective headwind over the rider. Three times the wind speed.
Nine times the drag. That’s in theory.
Tailwinds make more difference on fast segments. Say it’s a flat sprint segment at 50kph - 5kph headwind vs 5kph tailwind is nearly half as much drag again.
Hand waving assertion: it takes [b]no where near 250W[/b] to hold 40k in a tailwind on the flat, effectively the same as riding at 20k in still wind - 12.5 mph!
To sustain a speed of 40kmh I’d imagine you’d need a pretty nice tailwind, or be riding in a bunch, or both.
Depends on the length of the segment though. One minute? 30 minutes?. And are they pan flat roads or gently rolling? I don’t have any panflat roads so that’s a foreign thing for me... always a slight up or down.
Road surface is also a factor .
I reckon a 20km wind behind would enable me to ride at 25mph (approx 40 km/h) for around 200 watts on the drops on my fast bike.
With no wind I reckon to do 25mph I'd need close on 300 watts on same bike.
Into a 20km wind..well I don't think i could hit 25mph on the flat for very long ..but at a guess maybe 400-450 watts would get me there. I regularly ride into 20km winds and I reckon 220 watts gets me 18mph ish
Basing those numbers on what i see on the road bike, plus my power outputs on the tt bike (26 mph average for a 10 with no wind and a flattish course required 280 watts on a tt bike with all the slippery accessories). And my tt bike is considerably faster than the fast roadie.
Flat roads here!
Sockpuppet, hmm I'd say at least 200W to hold 40 kmh with a 20 kmh tailwind on the hoods, guesstimating from experience - what's your bet?
Just got back from a ride and it took me 522w to maintain 45 kmh for 1 min on a flat road with a very slight tailwind, flat back on the hoods..
Well if we’re guessing...!
20k is a decent tailwind. I can average 30kph for over two hours on my road bike on a pretty loop (so taking wind out of it). No idea how much power I put out to do that.
But riding at 40 in a good tailwind on the flat isn’t that hard. Just like riding at 20 on a nice calm day isn’t hard.
I’m going to guess 138.6W.
These wind variations you’re talking about aren’t that big?, more like a spring or summer breeze? They seem like a fairly light wind. It’s when it gets to 35 or 40kmh winds that I start to notice a big difference 🤔... or maybe that’s just me 🤫🤷♂️
Looking at one of my 2 mile segments, with my power meter on my winter bike, 203 watts and 23mph (over the 2 miles it’s 0.3% downhill). Wind was 5.1mph ENE. Total time was 5:18.
Same segment, with an 11.9mph SE wind (same bike, same wheels, same tyres and same power meter), 227 watts, 25.9mph and time of 4:42.
Not sure if that helps, was just trying to find a 40kph segment that I’ve repeated with a power meter and different wind directions.
The downside is that it’s not a straight line, typical winding countryside roads.
Time to go out and ride at 40 kph back and forth on straight roads with an anemometer
and see what the powermeter says.. :p
Wow, roadcyclists are an obsessive bunch.. https://science4performance.com/2017/02/24/the-best-wind-for-a-kom-on-strava/ hehe
No clue on watts but from experience of prevailing westerlies and my commute on a flat cyckepath to Morecambe a big storm can crush you or make you. With 60moh tail winds a relatively unfit beer monster can match semi pros on a still day.
Tailwind descent down a big steep hill (Jubille Tower) got me to 94kph.
Tailwind are to roadies what a dry Lakeland bog is to mountain bikers, it's not cheating, its make the most of the conditions... Sreava for scoring points is however one big cheating waste of time.
Drag changes with the square of airspeed.
Yes, but power is drag x speed. With no wind, it takes 8 times as much power to double speed.
Wind speed in weather forecasts is measured 10m off the ground.
The actual wind speed experienced when riding will usually be much lower than the forecast suggests.
Exactly, unless you are measuring windspeed and yaw with some very clever device on your bike then everything is just a total guess.
Drag changes with the square of airspeed.
Yes, but power is drag x speed. With no wind, it takes 8 times as much power to double speed.
Ok, I wondered about going down this rabbit hole...
Yes, for aircraft power required goes with the cube of speed. Work done is force times distance, and when you increase the speed you travel further in the same time so effectively apply the force over a longer distance, as well as the force being increases because it must balance the drag which changes with the square of speed.
This is definitely correct. Which is why jets cruise at the speeds they do. Fuel needed goes up massively even for a small cruise Mach increase, while flight time only drops by a few minutes, so it rarely makes sense to go faster.
But an aircraft is applying force to the air it’s flying through.
A bike is applying force to the road, through the drive train. At 40k (say) and in same gear is always applying the force over a fixed distance.
In this specific case (fixed speed, headwind varying) I think that the power goes with the square of the wind speed over the rider (which is 40k plus/minus the wind over the ground).
Now, wait for it...
If you start changing more things, like speeds, or gears, it all gets harder to explain convincingly. And you may recognise this situation.
Yes, it’s the treadmill thing again. And no, the cyclist *does not* get airborne.
Back when power meters first became 'accessible' ie didn't need their own hub I used an online watts calculator to get the avg power I'd need to beat a time on a local climb. I found it the 'easiest' way to do it - I'd know I needed 340w avg for the duration of the climb, so hit LAP at the bottom and just gurn at the avg power number all the way up.
I know these days you can plug a virtual partner into your garmin and try to hang on, but the calculator was always very accurate for a long, steady climb and had the windspeed variable so no reason to doubt that would work.
Based upon last night’s ride which was an out and back of 30 miles with the wind from the east so headwind out, tailwind back given the curving of the road.
Taking the 10 miles in the middle each way and using average speed and normalised power from a crank meter, I was 1.9mph faster on the return with a tailwind for the same wattage (within +/-5w).
Steel road bike, 50mm wheels, no aero kit and just into tempo hr.
To add; the only difference I felt was that it was nice to have a tailwind home for a change.