I heard from a friend that there is absolutely no benefit to riding in an aero position when your speed drops below about 15mph.
You may as well give yourself a posture break and sit up.
Is this true?
And is 15mph the magic number?
It makes sense to me.
You need to understand that air is basically a fluid you are moving through. At any speed, something more aerodynamic will allow that air to move past you faster and with less drag. There is no magic speed number that aerodynamics suddenly becomes important. That would be like saying “the aerodynamics of an airplane wing don’t really help until 400 mph”. Anything aero helps at any speed
I heard from a friend that there is absolutely no benefit to riding in an aero position when your speed drops below about 15mph.
Not true, but if your friend’s in the same age group you should tell them that it’s actually anything less than 25mph.
This visualizes it pretty well. Both your friend and the above poster each have a point.
More aero is always better. According to the below, already the dominant drag factor around 10MPH.
But your friend is right that most people have no problem sitting up around 10-15MPH. But I think the primary reason for that is that speed - at least for racers - is low enough that most aren’t at a high % of FTP, so the extra bit of power needed to overcome drag is pretty negligible.
But if you’re at 15MPH at 80% FTP, then it’d matter.
As mentioned, obviously being more aero always helps, but at lower speeds difference to other losses become smaller. Typically when going 15mph or below, one is climbing and a position where lots of torque can be produced starts to become more important.
Btw. 15 mph is about the average speed of the pro’s when doing big mountain climbs in TdF or Giro, they still like to be behind people at those speeds.
For what its worth I remember a pro (Rapp?) doing a wind tunnel test and for them around 20kph was the magic number where sitting up meant they could produce more power than what they would give up in drag.
I heard from a friend that there is absolutely no benefit to riding in an aero position when your speed drops below about 15mph.
You may as well give yourself a posture break and sit up.
Is this true?
And is 15mph the magic number?
It makes sense to me.
I heard from a friend that there is absolutely no benefit to riding in an aero position when your speed drops below about 15mph.
You may as well give yourself a posture break and sit up.
Is this true?
And is 15mph the magic number?
It makes sense to me.
One ultra important aspect that many cyclists fail to keep in mind is that aerodynamic drag is dependent on your airspeed rather than ground speed. So all those folks sitting up and grinding along at 12mph in the wind tunnel that often exists on the way back to Lake Placid into a 15 mph headwind are really seeing the the drag generated by an effective headwind of 27mph rather than 12mph. By sitting up they are making themselves into huge parachutes and really killing their speed.
The converse is that if you’re hauling along at 32 mph with a 20 mph tail wind may well be a great time to sit up a bit, drink or feed and stretch your back since your effective head wind is only 12mph.
Hugh
+1. You have to consider airspeed, not ground speed. I’ve had 30mph tailwinds, so just going easy at 36mph, nearly spun out. As I went up inclines, the relative wind speed actually became negative, so sitting up meant I was a big sail.
It’s worthwhile studying the weather.com report and course map to determine since speed an direction during your event. Wind is the same as someone changing the route and adding a really, really long hill or downhill.
FWIM, Zipps make a really errie sound at 35+mph when there’s no wind to act as white noise locking it out. It actually gets a little annoying after 20 minutes or so. Though not as much as riding into that headwind.
Off topic… does anyone else, on a rural road in the middle of nowhere, ever hit their turn around point after riding into a headwind for 1 hour+, shout out some loud “wohooos!” as they turn around, stand up and feel that awesome tail wind for the first time?
Then you look down as realize the pro tour riders can hold that speed in a TT, on flat ground with no wind aide… and you feel a little weak.
For what its worth I remember a pro (Rapp?) doing a wind tunnel test and for them around 20kph was the magic number where sitting up meant they could produce more power than what they would give up in drag.
It’s about that. 14mph is what I’ve always used as a rough guide, and that was basically confirmed in the tunnel.
As long as power isn’t reduced you should stay aero all the way down to 1mph
There is no magic number, it is a continuous function.
I heard from a friend that there is absolutely no benefit to riding in an aero position when your speed drops below about 15mph.
You may as well give yourself a posture break and sit up.
Is this true?
And is 15mph the magic number?
It makes sense to me.
I heard from a friend that there is absolutely no benefit to riding in an aero position when your speed drops below about 15mph.
I assume this is racing, and you are on a climb going that slow…
If that is the case, and you can make more power sitting up, then it is probably true… because aero drag will be a pretty small fraction compared to the power required for the grade.
But it isn’t linear. So power lost at 15mph is a lot less than power lost at 40 mph.
There are two variables that we can easily change on the drag equation (see Wikipedia for equation), but for a simplified equation I will use Drag = CdA X DF. Bike riders can change the aerodynamic position (CdA) and or speed (DF). Drag for this exercise is Velocity squared.
MPH Drag Factor (DF)
10 100
11 121
12 144
13 169
14 196
15 225
20 400
25 625
28 784
While the Coefficient of Drag (CdA) changes based upon type of equipment and position used.
You can decide for yourself where the break point should be when going into and out of aero. But notice the drag factor doubles between 14 and 20 MPH while the velocity only increases by a factor 1.4 and then the drag factor triples between 14 and 25 MPH while speed only increases (velocity) by a factor of 1.78!
Or by doubling the speed from 10 to 20 MPH drag increases by a factor of 4!
Now if you have a power meter you can correlate required power to speed in and out of aero. I think the iBike power meter (not really a power meter, but close enough) will tell you your power and your coefficient of drag (CdA) in various bike positions and speed.
Totally agree with this, I did a TT recently with a strong head/tailwind, and I was actually getting out of the saddle at 35kph up a climb with the tailwind because there was hardly any air resistance and the extra 100W of power was well worth it.
The other thing you have to consider is the duration of the lower speed / higher power effort, as you’ll get a much bigger power increase from sitting up or getting out of the saddle for a short duration than a longer duration. If I could output 100W more power for an hour out of the saddle I’d be better off doing the entire TT out of the saddle, but I can’t, it’s only a useful approach for short durations.
as you’ll get a much bigger power increase from sitting up or getting out of the saddle for a short duration than a longer duration.
May you can. I don’t. I get max power in the aero position, or in the drops on the road. Not sure why, just do. Even in my indoor FTP tests where it’s OK to cheat in positino when the going gets tough, I get low.
Is that true for you even for a one off 1 minute max effort? I can do close to 700W for a minute out of the saddle up a climb, but not much more than 400W for a minute in the TT position on the flat. I could close the gap a bit with a less aero position, but it would be slower for longer durations where the power difference becomes negligible. Interesting how much difference there is between people for that sort of thing.
Is that true for you even for a one off 1 minute max effort?
Yeah. I do get out of the saddle for about 3-4 seconds or so to initiate an attack in track cycling. Very occasionally the same 3-4 seconds in road sprints. But my 1:00 max would be in saddle, and I’m an almost purely in-saddle climber. The only time I get out of the saddle on a climb is switch up muscle groups when I’m hurting, but my power invariably drops when I do that.
Yes, there is huge variation among people. I know I’m an outlier.
Yeah, I have gone as low as around 2 minutes testing this and it is the same for me TT or road bike.
It isn’t until the 30 second range where I need to get out of the saddle to get max power.
Which you would never, ever want to do in a TT except maybe the last 100 meters
as you’ll get a much bigger power increase from sitting up or getting out of the saddle for a short duration than a longer duration.
May you can. I don’t. I get max power in the aero position, or in the drops on the road. Not sure why, just do. Even in my indoor FTP tests where it’s OK to cheat in positino when the going gets tough, I get low.