Why Aerodynamics Matter At All Speeds
Aerodynamics has been the talk of the pro peloton, the bike manufacturers, and the local group ride for the last 10-15 years. It is becoming more and more accepted how important aerodynamics is for road racing. The number once force to overcome in a road race is easily aerodynamics. That is because of its relationship to speed. The faster you go, the more important it gets. While this is now fairly widely accepted, the questions of aerodynamics in gravel riding and racing are popping up left and right. This is partly due to the growing popularity, the increasing speeds, and frankly the commercial attention on this side of our sport. This brought us to our desire to find out what makes a fast gravel bike. Surely aero matters for the pros, but what about the majority of riders who are out there just trying to complete a new challenge. That is what grassroots gravel is all about anyways right?
Recently SILCA took one of our pro gravel racers, Dylan Johnson, to the wind tunnel to answer the question of how important is aero in gravel racing. When you are looking at a top 10 at unbound the answer is pretty easy, it makes a massive difference. Looking at a few of the graphs comparing power savings at different speeds we thought it might be important to highlight the story behind the numbers. This post is sure to be one for the marginal gainers and maybe (hopefully) bring a few of the skeptics over to our side. Aerodynamics matter for everybody trying to complete one of these big gravel adventures no matter the speed, and we will walk you through why.
Aerodynamics and Speed
It is now ubiquitously understood that the faster you go, the more aerodynamics matter on a bicycle. The question is, but how much or when do they stop mattering? The relationship between speed and power is relative to the cube of speed. If you have ever ridden a stretch of road at 20mph and it takes you 200w to do that, how much harder is it to go 25mph? 390w! Maybe you haven’t been able to quantify it, but we have all felt that. Over 80% of the forces slowing you down on a bike are caused by aerodynamic drag and the faster you go, the higher that number gets.
As a general rule of thumb to overcome the aero losses if you 2x speed, you 4x the drag, and 8x the power required to ride at that speed. This simplification of the math does leave out the linear relationships of rolling resistance and drivetrain efficiency, but it does give us a good rule of thumb to go off of. If you are going from 20 to 25mph, you simply do 253/203x200=390w.
When most companies are quoting power savings for a bike, helmet, clothing, etc, those are almost always quoted at the 40kph or 50kph numbers. When you do the math and bring them down to your typical gravel riding speeds of maybe 15-20mph, the savings or penalties become really small. That leads a lot of us to say “aero doesn’t matter for gravel.” It is an easy jump to make, but it is absolutely not the entire story.
When most people think about speed on a bicycle, they think about ground speed. How far you are traveling on the ground relative to the time it takes to do so. That is for the most part what is important for bike riding and racing because it will tell you how much time it will take you to get from the start to the finish line. The thing about aerodynamics is that it is all around wind speed.
Windspeed and Groundspeed
What does that mean for the person finishing Unbound 200 in 13 hours (about 15mph)? It means that if you are riding 12mph into a really stiff 18mph headwind, the aero savings you are looking at are now 30mph or about 50kph!
It is easy to look at a graph of the power savings of a particular equipment choice and say, “well I’m not getting in an aero position on the bike for an 11w gain.” For the entire 200 miles of a race like Unbound, that is probably a fair cost/benefit analysis that it is too uncomfortable to get into a really aero position for 11w of benefit. What about when you get that 18mph headwind though, and it all the sudden becomes a 90w gain? Most would agree that it is absolutely worth 90w to get down on your bars and get a little more aero in the headwind to save 90w of effort for the same speed.
The same can be said for running aero bars. Lifetime has banned them for the elite field here in 2023 but us amateurs can still ride them. When you are using them, our testing shows aero bars are worth about 15w at 15mph. That is far and away the biggest gain you are going to get on your bike, but is it really worth all the extra equipment, loss of hand position, etc for 15w? Maybe not. It certainly is worth the 120w at 50kph!
Between mile 50 and 60 at the 2022 edition of Unbound, the course went almost directly into a headwind so that is a perfect place to run our simulation. Estimating the time savings here is what we are really after. Our baseline of putting a respectable age group power of 180w average over this 10 mile stretch would take 55:49. The 120w savings from going to the aerobars with that headwind would save a whopping 14:12!
Aerodynamic Takeaways
We are not here to tell you how to ride your bike, simply to explain how you might be able to improve if you want to. If you look at some of our recent test data, it is really easy to look at it and say it doesn’t matter to be aerodynamic in gravel races because you aren’t going fast enough. That simply isn’t the whole picture.
If you are looking for some real world validation for this concept, think back to a ride where you had a massive tailwind. You are flying down the road while putting out seemingly no power, but you are riding at 25 or 30mph. You get out of your drops and take your hands off the bars and sit up. Not much happens. You drop 1 or 2 mph. That is the same thing in reverse. If you have a 20mph tailwind and are traveling at 25mph, the effective air speed you are facing is just 5mph. The aerodynamic drag on the rider is almost nothing that that point. The only forces you need to overcome are the rolling resistance and drivetrain losses on top of the minuscule aero penalty you might be facing.
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I’m reading the article and the responses and Michael hearing that question I think “everything.” Easy example my track bike has more drop but I also put narrower drop bars on it (38 instead of my usual 40). Short races in my slow cat 4 5-10min I don’t notice the deeper drop much but I REALLY don’t notice the narrower hand position which I figured would have SOME effect but was worth it for tight pack small space but likely more aero too and as the gravel example maybe I cant hold as narrow a grip for hours but there was VERY strong “standards” that people used without ever considering this. Riding 42’s? Try 40s or even 38s and build up to using them…on a more technical course this is a bad idea but if aero bars are manageable clearly this would be.
2) Why do all the drop bars now have shallow drops? Because no one uses their drops because they have unrealistic ideas about where the bars should be. On my old commuter I have deeper way deeper drop from tops to down in drops … it got me thinking…sure you don’t \want to spend all day down there, but why not have a deeper “go to” for those headwind times?
3) Sounds like you can’t have funky bars (are those ones with the horizontal bar below the tops legal still?) but nothing to keep you from gripping the bars narrower AT LEAST for “those” sections.
4) Some very experienced fitter told me pros don’t stretch much they’re just more flexible. I stretch and when I do I am naturally pretty flexible but I get MORE flexible…so….people can stretch and be more comfortable in a position that is more aero over time IF
5) IF they train in it. So indoor intervals…do people ride in the drops for non-climbing like simulated efforts? I’m guessing very few. I knew this was important (train in position you want the power in) and it feels even harder indoors but I didn’t let “better” be the enemy of “try and good?” And did it MORE … if I got more gassed then I felt like I should be I eased up on my position….over time I got used to and more comfortable hammering in the drops for over an hours (yes gravel is much longer) for crit and 2×20s. Are people realistic about their positions, creating more options that are available, putting in the mental work to work ON their position as a thing, physically and mentally doing it “the hard way” even indoors at least sometimes and then more and more?
6) I have an usuallly long torso and very long “reach could go further but loooking at others realizing they aren’t (I have a 120-130 stem on drop bar bikes… 5’10” 56cm madone (H1) 120mm stem. It’s cramped to go narrow if the bars are close. What about a longer stem to facilitate that feeling, with longer drops coming back, deeper drops from the tops so can go up in aero when not needed, narrow with hands on bars yes I’m sure that’s required but elbows low (people do this on the hoods but if able to aero bar then sorta like “invisible aero bars” but using hands and a longer cockpit with more handlebar position options.
6) I really like Silca’s thinking here which is different from “Ironman triathlon position higher” here thinking “way lower SOMETIMES” so even if SOME of the above is less comfortable (not necessarily if trained but sure there’s a limit) use a scalpel not a sword to slice the sections why limit oneself (as they point out) even at shorter critical moments?
7) Wow long comment I know this reminds me of some general things: working on position? No one’s interested. Intervals IN racing position? Dunno some probably most amateur I doubt it (and good data on that triathletes are stronger on the (lower) aerobars than higher since they train on dedicated aerobar bikes. Spend years working on one’s fit because can’t get comfortable in the drops or do then go numb can’t have to worry about that. Took me over two years innumerable saddles, bunch of handlebars and a very extreme (to most) shortening of crankarms (I’m a duck basically leg wise …penguin? But it was a $200 “test and see” experiment I’m glad I did.If it’s tiring and not worth reading to hear … I can’t imagine that most are reading and asking and trying EVERYTHING for years that aren’t (see above) high tech (at all?) but take a ton of mental work (and not “suffering” just like not mindless riding which I appreciate doing too it’s much more “work” to “work on” is this newer position going to work am I going in the right direction. Hearing “pros need to be flexible but don’t (often? Mostly?) stretch much so people who aren’t naturally flexible can’t be pros suggests to me (let’s go with that that may be true to some degree at least it was from a good source who would know) that wow don’t 99/100 people then think “whelp stretching is crucial sounds like lemme stretch consistently for years?” I’m not saying no one will I’m saying it sounds like no one is. Back to silca’s article…it’s not the tech…it’s the work and solving the puzzle over time and then doing the work to make the best solution fit as best it can rinse repeat. I’ll really go out on a limb here and ask: how do you prove something is impossible? ;-)
I remember reading about aero savings by having a few days stubble (legs & face); the dimpled gold ball or fuzzy tennis ball analogy. This was way before I’d heard the term marginal gains, but I still can’t find anything on it. Given the astonishing numbers we now have on aero socks, gloves, etc., seems like it’d be well worth investigating.
Thoughts?
Johnny O’
Terrific info and hope Dylan has found something he can use since Lifetime has taken away his aero bars for both Unbound and Leadville. Yes, Leadville too where LIfetime is banning them on all bikes, amateurs included. The gain at Leadville is more “Marginal” in that average speeds are lower and opportunity to ride in aero bars is less. So riders might be thinking “I’ll run some bar-ins to create a secondary hand position and an opportunity to get narrow and low.” Wrong again. Lifetime has said no to any kind of handlebar paraphernalia that extends from the bars. Drop bars are still allowed. So the question for Dylan and others at Lifetime’s other marquee event will be “what can I do?” to get low and get narrow.
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