Anyone know of any aero studies they can point me towards where they tested the rider in the reverse direction from normal head on ?
I was interested in trying to figure out at what wind speed delta ( rider forward speed versus tail wind speed ) that it makes sense to “sit up” and try and catch the tail wind more. Maybe never ?
Anyone know of any aero studies they can point me towards where they tested the rider in the reverse direction from normal head on ?
I was interested in trying to figure out at what wind speed delta ( rider forward speed versus tail wind speed ) that it makes sense to “sit up” and try and catch the tail wind more. Maybe never ?
You don’t need a wind tunnel for this one, just some personal observation as you ride. Do you feel any wind coming from in front of you? No? Then sitting up won’t slow you down any. Do you feel any wind on your back? If so, the sitting up will make you get a little push forward.
But, about the only time this might happen for most people is when they’re climbing and moving pretty slowly. And as I’ve heard someone say before, if you don’t feel any wind on your face, pedal faster until you do!
This brings back memories of IMSG 2012 with the crazy tailwind pushing us down the main road from Veyo that goes back to St George itself… wind gusts suddenly giving you a massive acceleration which would come at times at an angle so it would suddenly accelerate you but also try to push you off the road. Scared the crap out of me.
This has relevance (Directly downwind faster than the wind):
I would think that if the tail wind is slower than your speed then you’re better off being low in an aero position but if the wind speed is higher then you should sit up and use your body like a spinnaker sail.
But that is sort of the question .
If I’m going slower than the wind speed behind me while I’m tucked down , would I actually pick up speed, for the same power output, if I sat up and tried to catch the tail wind.
I assume this would come into play more for the average person , not as much forward speed, than a pro where the forward speed
is higher. 10-20 versus 20-20.
I assume the testing would have to be done at slower wind speeds since it’s the delta not the absolute value that is of interest, Is that correct?
Back in the late '80’s we were testing at the tunnel and got interested in this. This was right at the beginning of “aerobars” so the positions were not real low and the bikes were pretty standard. The aero drag was about the same over the rider forwards or backwards but at the yaw angles it showed some strong bike steering reactions, I looked briefly for some old results but haven’t found them yet. I believe we decided that if the wind was strong enough to actually push you along, it would be very hard to ride outside that day because of the changing directions. Then we calculated that a strong tailwind should be looked at more like a good drag reduction, like going to aerobars vs no aerobars or having a deep frt/disc wheelset vs std. 32* spoke wheels. I suggest that if you catch a really strong tailwind, get in your most powerful position and pedal hard to take advantage of it.
Anyone know of any aero studies they can point me towards where they tested the rider in the reverse direction from normal head on ?
I was interested in trying to figure out at what wind speed delta ( rider forward speed versus tail wind speed ) that it makes sense to “sit up” and try and catch the tail wind more. Maybe never ?
You not looking at thsi the right way. You should ALWAYS consider relative wind speed, never, ever ground speed. That only matters for rolling resistance and rotating drag of rotating parts.
Most data seems to indicate that 10-14mph is the range where its’ better to sit-up. It depends also if you make better power sitting up than when aero. Personally, I do not, it’s generally about the same and depends on how much I’ve been running and how fatigued my glutes are. Sitting up probably isn’t helpful to running well off the bike, especially if you don’t train that way a lot.
So if you moving at 18mph, and there’s a 6mph tailwind, your relative forward speed is 12mph. You need ot consider vectors too. So a 10 mph cross tailwind is only a 5mph directly behind you, so you woudln;t sit up until 15-19mph.
If you ride enough, you get a sense of relative headwind, mostly from the sensation of less evaporative cooling (you get warmer)
Tape a piece of string to your aerobars. If it points towards you, stay in aero. If it points away from you, you can sit up (because you are probably at a stop light).
You not looking at thsi the right way. You should ALWAYS consider relative wind speed, never, ever ground speed. That only matters for rolling resistance and rotating drag of rotating parts.
I think that’s basically right, but there are other forces at work in addition to the apparent wind that make things pretty complex. Sailboats go faster than the wind speed when in close reach, where the wind is actually coming slightly from the front (and also any time they are not heading directly downwind). The reason is similar to a wing, where the sail creates “lift” that pulls the boat forward. The same thing happens to a lesser extent with your body/bike/disc wheel when you bike with a side wind, which is why CdA drops with yaw angle. At the right apparent wind angle, disc wheels have negative drag and push you forward.
I’m not really sure whether a more aero position does this better or not, but I would guess it might? I’m pretty confident that the optimal position for a no wind situation must be different than the optimal position for a sidewind though. The question is, with a straight block tailwind, power aside, is it simply a matter of sit all the way up when the apparent wind is behind and all the way aero when the apparent wind is ahead? I just don’t know. It would depend on how much of a sail effect your body/bike produces. With no sail effect all the answers above are clearly correct, but with the sail effect, who knows? Maybe you should always maintain aero to get a better sail effect? (or possibly it goes the other way)
Hello southwick and All,
Your powermeter and speedometer should be helpful … since the wind is generally variable and you need real time data …
Position yourself for most speed with least power (or at your planned power level) … modified for sustained ability to maintain the position for the required interval.
Tape a piece of string to your aerobars. If it points towards you, stay in aero. If it points away from you, you can sit up (because you are probably at a stop light).
Seems legit, +1 from me
I once had a tailwind on a long flat straight road. I averaged 53kph for a touch over 15km…then turned into a horrible cross wind. I sat up during the tailwind.