Watts gained: Units? Watts/?/? Passive vs Active?

Ok, so this topic seems to be discussed fanatically everywhere I look. But I don’t really know what it means or how it relates to my training/performance etc.

So, let’s say I get some aero socks (hopefully they’ll stay up in the rain ;-). Suppose the manufacturer claims a 5 watt savings. 5 watts in what way? I’m guessing they would have tested this in a wind tunnel or simulation, but what was the wind speed (how fast was the cyclist going assuming no natural wind)?

Is there a universal set of parameters and units that all manufacturers have agreed on so we can compare apples to apples?

Now for a thought experiment. Suppose I’m riding at 100 watts for 30 minutes and cover 5 miles. Now I do the exact same ride with my new shiny socks which save 5 watts. Assume all other factors are equal.

Does this mean I would go farther with the socks at 100 watts and 30 minutes (e.g. as if I was outputting 105 watts)? Or, is it that I would cover the same distance in the same time only outputting 95 watts? (Doesn’t seem like these would have the same effect on heart rate, perceived effort etc.)

Also, it seems like there are so many of these gains/savings out there, but little discussion on the types/categories. For example:

  1. Passive gains: aerodynamics in clothing, equipment. etc.
  2. Semi passive: nutrition (optimized for performance and body weight), drafting
  3. Active: holding a better position temporarily, descent position, TRAINING :open_mouth:

Also, some of these items will flip depending on terrain and conditions. As a heavy rider my weight reduces my power to speed ratio compared to the ratio on a flat or descent.

Aerodynamic gains are way bigger on a descent compared to a climb. My shiny 5 watt socks don’t make any difference on the ascent, but going back down definitely makes a difference.

This of course is common sense, but doesn’t help me decide between multiple options, or how figure out how it will affect my ride.



Nope. And sometimes they don’t tell you the conditions for the reported gains.

Somebody will come along and post more, but aero starts with body position. All the other stuff slowly adds up, stuff like body suit, wheels, tires, handlebars, helmet, socks, etc.

Practically speaking, all those aero gains reduce your time. For example latest Dylan Johnson YouTube video, just looking at fork in the wind tunnel:

over 200 miles of Unbound, replacing the stock fork with the Lauf Grit on his Felt bike, would save 83 seconds (1 minute 23 seconds) over the entire ~200 mile course when ridden at an average speed of 32kph / 19.9mph.

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Definitely not! :grin: And sometimes manufacturers use this to their advantage…I remember GCN touting a castelli speedsuit that was a number of whats faster at 15% yaw…and I told them Castelli was marketing to the segment of riders that did not know what their typical yaw distribution was.

If you geek out on aero enough you can kind of move the yaw/speed ‘slider’ in your brain and visualize what bits & parts you want on the bike.

When you see a watts saved number you should be thinking ‘at what speed?’ ‘at what yaw?’ ‘is that a composite number?’ ‘is that in a velodrome?’ All important stuff to know along with what your yaw distribution is likely to be under different riding conditions.

Or, you could just bin it all & have fun riding your bike without regard to aerodynamics.


+1 on the Fun!

Good to know I’m on the right track on the inconsistency in reported gains. I have incorporated some aero improvements like position and helmet, but I don’t think I’ll ever be able to quantify the gains from them. What I do know is that aero gains = fun gains on fast descents! :astonished: :sweat_smile:

I have no idea what yaw is, but I have a feeling my eyes will glaze over with an explanation :no_mouth:

I’ll have a look at the video. He’s got some interesting stuff on his channel. :ok_hand:

It’s usually at a very high speed. For example, 5 watt savings at 30mph. This is typically misunderstood by consumers to think they get 5 watts on ftp or something of the sort. The confusing is probably part of the marketing technique. You would probably save 0.25 watts at any speed you will actually travel at, which is essentially useless

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Not if I do 10 of those things! That’s 2.5 watts!!!



The world tour peloton usually almost averages 30mph, so it does matter for them. But it’s like watching nascar and thinking I might go make some modifications to my Honda civic I use to go to the grocery store and back. But on the other hand, spending $$$ is what makes the world go around so spend it if you’ve got it!
->guy who rides a $5000 bike 6 hours per week lol!

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P12 weekday rides around here are 28-30mph average for 30+ minutes. Yeah its flat here but so what. Even I’m averaging 23-25mph on those 30+ minute hard pushes on group rides.

My favorite way to do threshold intervals is on longer Strava segments like this one:

solo, low, & aero. But I can’t hold a candle to the P12 crowd.

Every little bit of aero helps!

I feel your pain. This is why it makes sense to quote savings in terms of improvements in CdA or Crr or weight. Those things are (mostly) independent of speed over the range of speed that most cyclists ride.


Always feel the term “saved” Watts is misleading, because, as the OP says, you’ll likely put out the same amount of Watts, you just go faster for them. You could obviously actually “save” the Watts and pedal less hard, but because drag isn’t linear, that will make you go slower non-linearly and again change the “saved Watts” number…

In my view, you have 3 types of possible improvements:

  • Training: makes you go harder for longer if properly fueled
  • Nutrition: helps you go longer
  • Resistance: In the end, you will go faster if it’s a better aero or less resistance. In that category, you find aero socks, wheels, body position on the bike, aero frame, skinsuit, tires, etc

The fact that the latter is “commonly” mentioned in Watts is wrong, it should be done in crr (rolling resistance) or cda (frontal surface).
Less resistance matters anyway if you go faster than 15km/h. The speed gains will not be enormous, but since you’re slower, your low gain will be applied for longer, making you spend less time on a given course.

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