FLO Aerodynamics and Bike Wheels (Faster by FLO Podcast #57)


This is “Faster,” a podcast by FLO Cycling. In each episode, we interviewed industry experts to educate you, challenge you, and even change the way you train so you become faster. When we’re not creating this podcast, we’re working on other ways to make you faster. At FLO, we design and manufacture some of the world’s fastest cycling wheels that we sell consumer direct to keep more money in your pockets. As a special thank you for listening to “Faster,” we wanted to offer you 20% off your next purchase. Simply use coupon code, PODCAST, in all capital letters, at checkout. Your purchase will also support our give back initiatives. One percent of all sales supports our Bike for a Kid program, where we provide bikes and helmets for kids in need. We also plant one tree for every wheel we ship as a thank you to our planet. Enjoy the show.

Aerodynamics and Bike Wheels

Hey, welcome back to “Faster.” This is part two of our mini-series. And today we’re going to be talking about aerodynamics. This is kind of our bread and butter. It’s the thing that got us started, making aerodynamic cycling wheels. So we’re excited to talk about a number of things aerodynamically today. Aerodynamics can be something that is very confusing. Sometimes there’s a lot of myths. There’s a lot of things out there that just aren’t quite true. So we’re going to kind of break everything down, start at a very basic level, discuss some terms, what they mean, give some sort of visual examples so that you can understand what it means and why it would be important for you as a cyclist. And the further we get into this, we’ll start talking about things like weight and aerodynamics and which one’s more important, different courses and how that looks, things like tires, tire sizing, aerodynamics and cycling in general too, not just wheel stuff. So let’s get started.

What are areodynamics?

So let’s look at a few terms. Aerodynamics itself is considered the study of air interacting around moving objects. So there’s a couple of things when you think about air as a fluid. And most times, when people think of a fluid, they think of like water or a liquid. But air and water are both fluids. They’re just in different states, one’s a gas and one’s a liquid. So aerodynamics is the study of airflow around objects. Hydrodynamics would be the study of like water or a fluid, like a liquid fluid, around an object. So, in these examples, a lot of times we’ll talk about like a canoe in the water because you can see like ripples and it makes it easy to visualize. And another really good example is a hand out the window. So it kind of helps you see things and understand why aerodynamics becomes important.

What is drag?

So the next term we’ll talk about is drag. And drag is a force that resists a body moving through a fluid. So if you think of a force, I mean, if you put your hand on the wall and you push on the wall, you’re pushing on the wall with a force. If you are moving something through a fluid, there is a force that resists that body moving to that fluid. So, an example, I always like to give because everyone’s done this, if you’re driving down the road and your window is open and you put your hand out the window, if you put your hand sort of like an airplane wing, it’s easy, it sort of cuts through the air, so your hand is basically moving through the air at a very fast speed because the car is moving fast. And you can still feel some sort of push backwards. But if you turn your hand sort of sideways, where your palm is facing forward, your hand gets shot back really quickly to the sort of the back of the window. So that means that there’s a much greater drag force that is moving your hand backwards. And so, from an aerodynamics perspective, when we look at it from a wheel design, we’re trying to make your hand a lot more like the one that looks like an airplane wings, so it cuts through the air, versus the one that’s straight up and downward where it pushes you backwards. So you save a lot of watts when you have a more aerodynamic wheel.

Now, it’s more complex than that. You don’t want it just to be a thin shape. And we’ll talk more about that in a bit. But that’s the basic concept of drag. Another way that you can think about drag and sort of visualize the fluid is if you think of a canoe in the water. So if you’ve ever been on like a very still lake and you’re in a canoe, and you’re moving the boat through the water, you can see ripples forming at the front of the boat. And so, you can see that the boat itself is moving through that fluid, which in this case is the water, and you’re dispersing, meaning you’re moving that water around the canoe. So as you’re moving that, you’re changing the fluid, and so it creates a loss of energy. It takes work to get through that fluid. And you want to make that as streamlined as possible.

Shapes, we talked a little bit about. So anything that is sort of thinner and sometimes depending on the roundness, but rounder, smoother edges like an airplane wing become more aerodynamic. Things that are blunter like a sheet of plywood sideways is very blunt. Everyone can kind of imagine if you were walking out in a windstorm holding a sheet of plywood, that would not be a good thing. So, in that case, the drag is basically on the sheet of plywood, and so it’s just pushing you along with it. So shapes have a very important component of aerodynamics and how to reduce that drag.

What is YAW?

Another important thing to think about, especially in cycling wheels, and it’s different in… A lot of people think of aerodynamics like from an airplane perspective. And we’ll talk about that a little bit more in a minute. But what we’re going to look at is something called a yaw angle in a cycling wheel. And so yaw angle, from a relative perspective, would be the same thing as an angle of attack on an airplane wing. So if you think of cycling wheel that is going straight down the road, you’re not turning your handlebars or anything like that and there’s absolutely zero airflow, so there’s no wind moving anywhere, when you’re going down the road, the front edge of your tire, so basically the crown, the highest point in your tire, is hitting the air first and that is what’s considered your leading edge, and there’s no angle, so the wind hits you directly on that crown of that tire. So that would mean that your yaw angle in that case was zero. If the wind starts to blow and it blows directly at you, well, your yaw angle is still zero because it’s blowing right at that crown of that tire.

What the yaw angle means is that if the airflow is blowing directly at you, let’s say that it was to blow directly at you from your right side, so it’s going to go directly into like your right shoulder, well, if we’re stationary, we’re not moving, and the velocity and the vectors and how it all adds up plays into that angle, but that would be a 90 degree yaw angle, it’s hitting you directly at 90 degrees. When you measure yaw angles, what you do…and we’ve done this, this is one of the big studies that we did back in 2015 and ’16, is we mounted a what’s called an anemometer. It’s basically a weather vane, weather sensor. And there’s other companies that do this now with some different technology. They use like pitot tubes. And it allows you to measure the incoming angle of the airflow.

Our YAW Testing Results

So, in all of our work, we’re one of the first companies to do it, I think we were the first company to do it, we discovered that the average yaw angle that you see is anywhere between minus five and plus five. Now, what that means is if the very crown of the tire is at zero degrees yaw angle, if I go to the left, if I open up one degree, so you’re thinking when you say open up one degree, it’s like you’re looking down from above at the top of your front wheel, and like I say, over all the way to your right would be positive 90, over all the way to the left would be minus 90. And so one degree would just be one degree away from the zero. So you’re 89 degrees from all the way from your right, and then minus 1 would be minus 89 degrees all the way from your left side. So that’s plus and minus 90s. So 80% of your time as a cyclist, you are experiencing anywhere between minus five and five degrees of yaw. Beyond that, most of your time, I think it’s in the 90s is spent between minus 10 and plus 10, so really outside of that. There’s not a ton of yaw angles that you see.

And then when we did all this testing, we rode everywhere. We rode along the coast, an ocean side which is an Ironman course, you’re getting a lot of coastal breeze. We rode through Ironman St. George. We did testing in Ironman Kona. We rode the old Silverman course here in Las Vegas. We rode through Mount Charleston here, which is a wooded area. We rode in groups. We rode along different roads. We tested it all over the place. And regardless of where we went, the average stays roughly in that same area. So what you see as a cyclist is very consistent. Another thing that’s really important to understand is something called relative velocity. So relative velocity means how fast are you moving your body relative to the air itself? So if the air isn’t moving, there’s no wind, whatever your speed is, whatever speed you’re moving along the ground, your ground speed, is your relative velocity. So let’s say that you’re going 10 miles an hour, you’re going 10 miles an hour down the road, 0 wind, that means that you have a relative velocity of 10 miles per hour.

If you have a headwind, meaning that the…and we’re not going to use yaw angles here, we’re just going to use zero yaw angle to make it simple to understand, but let’s assume for a second that the wind is blowing straight at you with a zero degree yaw angle, and it’s hitting you sort of like in the face. You’re going 10 miles an hour, but the wind moving towards you is also going 10 miles an hour. That means your relative velocity is the addition of those two. So it would be your 10 plus the 10 of the air moving at you. So remember, when we look at aerodynamics, it’s that body moving through the fluid. So if you were stationary and the wind was blowing at you, while you’re not moving, the air is technically moving around you, it’s still moving around you at 10 miles an hour. So when we go into that and add 10, it makes your relative velocity in that case 20 miles per hour. If you have a tailwind, so it’s hitting you directly from behind at 180 degrees, and let’s consider that that was also 10 miles per hour, well, then, if I’m going 10 miles an hour and the air is going 10 miles an hour in the same direction, that means that the relative velocity in that case is 0 because the air is not moving around me and I’m not moving through it. If it was only moving through or blowing behind me at five miles per hour, then that just takes away only five miles per hour. So technically, I’m moving through the air at five miles per hour. So any tailwind is subtracted from your ground speed, any headwind is added to your ground speed. So you’ll hear things like yaw angle you’ll hear things like relative velocity, drag, a number of other things. These are all sort of some of the basic terms that you’ll hear, especially in cycling when it comes to aerodynamics.

What makes a cycling wheel aerodynamic?

Now, there’s another term if we get a bit more a little bit more technical. A lot of people ask, “Well, what makes a cycling wheel aerodynamic?” There’s our disk wheel actually propels you forward, which means it acts like a sail. So that’s kind of weird, how would that work? And the simplest way to sort of explain it is if you think of an airplane, so an airplane, if you think of a plane, you’re looking at it from the sides, kind of like a profile view of an airplane, you can see that gravity is acting down. So think of an arrow on the top of the plane pushing it down, that’s gravity. Underneath the plane, there is a force vector that’s pushing it up. And that is considered the lift. So the lift is what you get from the wing. So as the plane moves through the air at a high velocity, high speed, it creates lift underneath the wing. And when that lift is greater than the force of gravity, so gravity is 9.81 meters per seconds squared, when it’s greater than the force of gravity, then the plane goes up. So it’s like if you and your friend had your hands together and you’re pushing at 9.81 and then your friend pushes back at 9.81, well, you’re not going to go anywhere. If your friend is pushing at 9.81 and you’re only pushing at 1, well, then gravity, in that case your friend’s gravity, is going to keep pushing you towards yourself, so you can’t go any further. But if you then push harder, then what’s going to happen is you’re going to push your friend the other way, so it lifts it up. So you think about it like an airplane wing, it’s called lift in an airplane wing. In a cycling wheel, it’s something called side force.So side force is important and it comes down to…there’s vector math that goes into this. But what you want is you want the…there’s a drag component, there’s an x and y component of a drag vector, and there’s an x and y component of a side force. So, when the component of side force that is opposing drag, so, again, just like your friend’s hands or the lift on an airplane wing, is greater than the drag value, then what happens is is you actually are pushing yourself or just like a sail on a sailboat. When drag is greater, then you are being held back, so the drag force is greater, and that means that it’s more difficult for you to move through the air than if you’re using something like a sail.

So what we as wheel designers do is we try to balance a number of things. We want to make sure that we have a really good amount of side force, which helps us create a very aerodynamic wheel. We also want to have a rim shape that is very aerodynamic. It interacts very well with the tire that we’re designing around. But we also want to create something that is a very stable wheel. So we could create a shape that may be super aerodynamic, but if you get it into any sort of crosswind, crosswind meaning that there’s some sort of yaw angle, it starts to be very unstable. Your handlebars start to twist if you get a gust coming from the side or anything like that. A lot of people say it’s like riding a bucking bronco, which is true if you’ve ever been on like a very old profile, something like a V-shaped profile, which is basically just a thin profile and you create a triangle all the way down to the spokes. Those were very rough and complicated to ride just because of how they handle.

The reason that’s important, and one of the ways that we balance for a cycling wheel is when we took all those measurements back in 2015 and ’16, I think it was 110,000 data points that we collected. So we were basically collecting data every second, and we just…I mean, we rode all over the place. But what you get is an algorithm that we then use in something called computational fluid dynamics software. And I think it’s important to talk about that for a minute. The reason we use computational fluid dynamics software is because when you are designing a wheel or anything aerodynamic for that matter, there isn’t an equation that says that you can solve to say that something is going to be fast. Aerodynamics is really a question of how much can I test and how many tests can I do? So original wheels were designed in wind tunnels. Companies would take maybe 10 to 12 different prototype shapes in. They would see what was faster, and then that would sort of be their mold. I mean, I’ve heard stories of things being made of like solid wood, plaster, very heavy things and aren’t even really…you couldn’t ride. But what they’re doing is they’re testing the aerodynamic properties.

Using CFD in Aero Wheel Design

And today, when we started, we started this about 10 years ago, our idea was…and not that other people hadn’t used CFD. We started with CFD. But by 2015, our idea, and we were the first ones to do this, was to create an algorithm that allowed us to study hundreds of rim shapes. So we used something called an optimization algorithm. So we collected all the on-road data, which gave us the yaw angles, the relative velocities that we knew cyclists experienced because while we could go into the wind tunnel and test 12 different shapes, if we didn’t know what a cyclist actually was experiencing, then how do we know what was going to be fast? Because maybe you’re really, really fast at 15 degrees of yaw, but we already know that 97% of your time it’s in between -10 and +10, so why even look at that wheel shape?

So the optimization algorithm had all of that information. There’s a weighted algorithm, which gives it an order of importance, which means that there’s a much higher importance on drag. But we also give it a weighted component for yaw torque, which means that we don’t want the wheel to twist in your hands. So we don’t always pick the fastest wheel. We pick the wheel that is very fast, maybe within a gram or two of drag. But if we give up a gram or two of drag, we may increase the stability by 20% to 30%, which overall makes you a faster cyclist because you’re not having to think about coming onto the bars or having to hit the brakes because you’re getting blown all over the road. The reason that it’s…going back now, so I’ll start my sidestep for computational fluid dynamic software and its importance. And like I say, the reason we use the optimization algorithm is because instead of taking 10 to 12 plaster molds or prototypes to a wind tunnel, we can use a supercomputer which we do and it iterates over hundreds of rim shapes. So we give it the algorithm, we give it a parameter set which is basically you’re allowed to design in this depth, this width with this tire shape, and then it just keeps testing, and testing, and testing until it basically solves, until it really can’t find anything faster in that box that is faster. And so that’s how we solve for the fastest rim shapes based on, like I say, tires and everything else.

And to date, we’ve not really seen a better way to do that. It’s solved at this point close to 10 different rim shapes. All of them are extremely fast. And if we ever go back to re-evaluate it, we don’t really find another or a faster option. So it’s really good to know that that works. When we didn’t use this, our first generation wheels did not use the optimization algorithm. And so we took random shapes that we put in CFD. They were fast, but what we noticed was that the first time we use the optimization algorithm on what was our flow 60 at the time, we made a 23% improvement, which is really, really high. The improvement on the newer wheels is much lower, probably in the maybe 7% to 8% range. And that’s because we included rolling resistance as well. But it just shows how effective the algorithm can be.

Wheel Twist and Leading Edges

So going back to the discussion on why a wheel will twist when you’re riding and if it’s not balanced properly, and it has to do with yaw angles. I want you to go back to thinking of your hand out the window, and we’re going to have it sort of forward. So your thumb is the first thing that’s hitting the air, or consider you don’t take your thumb away so you were just gonna look at the four fingers. So your pointer finger is the one that is hitting the air first. So it makes first contact. It’s like the crown of the tire at zero degrees of yaw. So when your hand is flat like an airplane wing, we’re going to consider that zero degrees of yaw. Now, I want you in your mind to open your fingers, so spread all your fingers apart. So if you do that, you have three other fingers behind that first finger. But they’re not seeing the air because the finger in front is breaking the air for them. Now, if I were to take my hand and I were to turn my hand up, so I’m taking my pinky finger drops and my pointer finger goes up, what you’re going to soon realize, and if you can try this out on a car if you want to, put your hand out the window, is that the airflow hits your first finger, but then at a certain angle, it also hits your middle finger, your ring finger, and your pinky finger. So that means that as opposed to having just what’s considered a leading edge, so the leading edge is what was at the zero degrees of yaw when your hand was flat like an airplane wing was the front of that pointer finger.

Now, as you rotate your hand, you would have in this case, four leading edges. You have your pinky, middle, ring, and pointer finger. On a cycling wheel, as soon as you get in any type of yaw angle, you have a two leading edges. And so what does that mean? The first leading edge that we’ve talked about is the tire itself. So the air hits that. A good way to visualize this is take a fan. So the fan is right in front of the cycling wheel. And you’re gonna sweep that fan out where it’s sort of…let’s call it at a 20 degree angle on the right side, so we open up 20 degrees. You can see that the air coming from the fan would still hit the front of the tire, which is the leading edge. But just like your hand with the fingers, the second back half of the rim, so basically where the spokes connect also becomes the leading edge. So you have the tire on the front half, that’s a leading edge, and you have the inside rim profile where the spokes connect, which is your second leading edge.

So that would be like if you took your middle finger and your ring finger away and you just had two fingers out and you rotated your hand, the front of your index finger is like the tire and the back of your pinky finger is like the inside of that rim. When that happens, if you have like a very pointy shape or something that doesn’t interact well with the wind, when that yaw angle happens and you hit that second leading edge, what happens is it creates a very high force on either the front or the back and it starts to twist the wheel and the handlebars, which is called a yaw torque. So there’s a force that wants to twist that wheel. So what we do is…so that goes back to that weighted algorithm, is we’re really balancing that as much as we can so we get that yaw torque as close to zero as possible. You could potentially get it to a very low number, but at the same time, your aerodynamics may go way out the window. So, again, it’s a very important balance for both of those things.

Using Data Trends in Aero Wheelset Design

One thing that we also look at when it comes to aerodynamics is we look for trends. There’s a lot of discussion about what is the fastest. And when you study something, how do you look at your shapes, how do you mold your tires, do you use spokes, do you use hubs and CFD? And we have always looked at it this way. Aerodynamics is so complex because the number of variables that go into anything testing-wise is extremely high. I’ll talk about that more when I talk about wind tunnels a little bit. But if you make a single change, let’s say that somebody is riding at 90 psi and somebody else is riding at 80 psi, that changes the shape of your tire because the higher pressure tire is a bit larger. That can change your aerodynamic drag by a big number. The fork of your bike, somebody may have like a Felt IA, somebody may have like a Trek Madone, those all interact with the wind differently. When you get to the back wheel, it’s a whole nother complex set of issues. The error has already gone through some of the bike, maybe your frame, maybe your legs, depending on the yaw angle. Your leg shape is different. The gear you’re in is different. The groupset that you use is different. Everything changes.

So if you really wanted to optimize somebody, a single person for just the perfect set of wheels for them, you could study everything that they do. You could map their body and basically scan it. You could understand their fit, their position, their frame. And you could design a set of wheels specifically around an individual that would make them very fast. That would be extremely expensive and would not necessarily make you all that much faster. You would see improvements, but you wouldn’t be much faster. So what we look for is we look for trends. Just like I said when we look at the yaw angle sweeps, we see averages. When we study yaw angles and CFD, we study the rim shape and the tire by itself. We do not use spokes. We do not use hubs. Some people argue against that. I think that it kind of gets confusing, especially when you’re looking at meshing. There’s different lacing patterns that are used. The front wheel is different than a rear wheel. Like I say, there’s different interactions with forks. There’s a number of other things. And what we do is we also look at spoke and lace wheels in the wind tunnel. So from a CFD perspective, we’re really trying to see what happens with a specific rim when we make a change to that rim. And we don’t want other things to confuse that.

So what we try to do is we look at things granularly where we reduce the number of variables to a certain point where we can get a very solid understanding of what’s happening. And then, we’ll increase complexity and we can look at things in more detail as we expand out around that. So, yeah, it’s a complex topic. There’s obviously differences of opinion that are out there. We’ve always had a lot of success with it. Like I say, our optimization algorithms have come out with a number of great things. We also look at things from what we consider a net watt reduction value. We used to call it net drag reduction value, but now we’re considering rolling resistance, which we’ll talk about more in the next episode. We look at it from a net watt perspective.

Using Real World YAW Data for Watt Reduction Savings

So what does that mean? When we did all the data collection and understanding what yaw angles that you ride at, there used to be a thought around the idea that if you were going to make a wheel that was fast, you take it to a wind tunnel, and you find, let’s say, like 17.5 degrees of yaw, it’s really, really low on the drag factor. So there are companies that would say, “Hey, we have the fastest wheels in the world. You save this much time,” and they looked at that singular point. Well, the truth is if you go out as a cyclist, you can’t make yourself ride at 17.5 degrees of yaw. So to us, it was always sort of a thing that made little sense. What we wanted to do is we wanted to collect all the data and understand the percentage of time that you spend at each yaw angle, which we did. So we basically used percentages from 0 to 1, 1 to 2, 1 to 3, all the way up to 20 degrees of yaw, which covers I think it’s like 98% or 99% plus of the amount of time that you in wind. And then what we did is in our algorithm, we solve for a rim shape that optimizes your drag in those buckets. So you don’t have to think about what yaw angle you’re riding at. You just know that you’re saving as much time as possible when you’re riding that wheel.

And so we call that our net watt reduction value because we look at drag, can be converted to an amount of watt saving. So what we do is we take a base wheel. We have always used a Mavic Open Pro, which is kind of like a standard OE wheel. We run that to the wind tunnel. It’s considered sort of our base wheel that we use to compare. And then we run our wheels with the same tire, same pressures. Everything else is calibrated the same. And then we can see the difference in drag value. And we know that by using our wheel versus that standard OE wheel, you’re going to save yourself X number of watts. And we call it the net watt reduction value because we’re looking at the whole range from – 20 to +20.

A Deeper Rim Does Not Always Equal a Faster Wheel

One thing we’ve learned over the years too is that a lot of times, people thought that the deeper the rim was, the faster it was. And in general, that’s not a bad approach. But we’ve also found recently that there’s a combination of rim depth and width to make something fast. So generally, what we do, if we’re going to design a wheel, let’s call it like our FLO 49 AS wheel, we give the optimizer a range of yaw angles, or a range of depths that it can hit. So let’s say it starts at 40 degrees of yaw…or sorry, 40 millimeters in depth, and then goes up to, let’s say, 50 millimeters of depth. For some reason, the optimizer optimizes and finds that a 50-millimeter wheel isn’t as fast as a 49-millimeter wheel. So there’s like a 1-millimeter discrepancy there. The 64 AS was designed over a range. It actually came in a bit lower. The FLO 77 had an upper range of 70. So it actually shaved off about 4-millimeters because it was 76 and change there. And it’s that combination of width and depth that create something that is very fast.

And yeah, it’s funny you always think that something deeper would be faster. But that’s not always the case. Tires play a very, very important role in aerodynamics. There’s been a lot of people that have claimed to design like tire wheel systems. It’s something that we’ve never done. The staple, the king of tires for a very, very long time aerodynamically was something called the Continental GP 4000 S2. There was a 23-millimeter size of that tire, which people used for years as a test tire. It was just known to be really, really fast aerodynamically and it is, it’s a great tire. Today, we’re using the Continental GP 5000s. And some of the things that we’ve learned over the years with tires are that some tires, same model, same brand can come from different molds. So there’s like mold 1, 2, 3, and 4. And some molds are faster than others, which would be very, very strange because you think you’re cutting something from a CNC. And so, it just goes to show you how small of a change can create a change in aerodynamics. We looked at tire pressure, so you go from like a 90 psi to a 85 psi. And we see differences in aerodynamics, sometimes up to 50 watts, which is huge. It’s a very, very big number. So tire pressure does matter.

When we go to a wind tunnel, we always calibrate it with highly accurate pressure gauge. We used to like basically shut off valves to make sure that we’re locking that airflow in there. So that gives us a very consistent test protocol. Tire treads are very important when we did all of the most recent work with our Gravel AS line…or sorry, Gravel line, not the AS line, the AS line is the All Sport line. There was this question around aerodynamics and gravel and mountain bike wheels for a very long time because there is this belief that a very aggressive knobby gravel or mountain bike tire could not be aerodynamic, that the airflow would just be too disturbed and that you couldn’t create an aerodynamic shape. So we wanted to try and see if we can improve that. It led to the release of our FLO G 700, which is a 700 C or 2900 I guess Gravel wheel. There’s the 650 B, which is called the G 600…or G 650, and both of those used, in testing, a very aggressive tread pattern. And what was really interesting is that we saw watt improvement. So if you looked at like a standard OE wheel for both road and gravel, so let’s say we use a Mavic One Pro, we use like a DT Swiss wheel for the 650 B, and we put on a Gravel tire, and we put on a road tire. So let’s just use the G 700, which is the Gravel version. And let’s use our FLO 64AS which is our All Sport line. The All Sport line is for road, the Gravel line is for gravel.

So if you look at the base, both used a Mavic Open Pro rim, and we put on a Continental GP 5000, a 28 mil, which is a road tire on the Mavic and we tested it. We put on a Riddler 37c, which is an aggressive gravel tire from a tread perspective on the Mavic Open Pro. And we tested it, and we put those same tires on our FLO 64 AS and our G700. And we tested those. We thought that based on all of our CFD work and things like that, we knew we’re gonna see an aerodynamic improvement when compared when we use the G700. over the Mavic Open Pro. But I guess what we didn’t expect was that the savings, the watt savings between the gravel and the road when compared to the Mavic Open Pro base wheel would be the same. So the watt savings for the 64 AS was 11 watts for the set. And for the G700, the watt savings was also 11 watts. So it kind of surprised us in some ways. Like I said, we knew we were going to be faster based on some of our preliminary CFD testing. But when we get to the wind tunnel, we noticed that regardless of tire, that you’re going to save the same amount, it’s as important to optimize your wheels aerodynamically in gravel as it is in road cycling. So that was really cool to find out. And like I say, we’re the first company, I believe, to develop such aggressive aero gravel wheels, first of its kind to be specifically signed around that and rolling resistance.

Front Wheel Aerodynamics vs. Rear Wheel Aerodynamics

We also get a number of questions around front wheel versus rear wheel, which is really great. We talked about that a little bit. The front wheel generally sees the air first. And a lot of people will call that clean air or laminar flow. So basically the air has not been disturbed. By the time it gets to the back, it’s kind of gone through a blender of legs, and spokes, and chains, and everything else. And so that air is dirtier, meaning that it can be turbulent, some of it reattaches to the wheel. Reattaching means that it goes back to laminar and sort of goes over the surface. We talked a little bit about laminar and turbulent. So if you think of a canoe in the water again, the ripples that sort of go around the boat, if they’re smooth and you’re going slow enough, you can see the lines of water sort of moving along the boat. And so the water sort of hugs the side of the boat. If you’ve ever been in like a speed boat and you’re going like very, very fast, you can actually detach. So you’ll get like pockets or bubbles that happen in that area. And so that creates a detached flow. In cycling, you want the air to stay as attached as long as possible on both sides of the wheel. It’s probably a bit too complex for this podcast. But, yeah, so basically, front wheel, air stays attached really well, which makes it fast. By the time it gets to the back wheel and it’s starting to make its way to those leading edges, the air sort of has to reattach. If it’s turbulent or if there’s some laminar stuff, it also has to stay on and be laminar. So your aerodynamic benefit on the front wheel is greater than your aerodynamic benefit on your rear wheel.

Tire Size and Aerodynamics

We also get a lot of questions around like tire size. So people will say, “Well, I’ve heard if you use a 23-millimeter tire up front and you use a 25-millimeter tire in the rear that you get the aero benefit of the tire up front, but you get like the rolling resistance benefit of the wheel in the rear And what we’ve realized is when you look at the combination of rolling resistance and aerodynamics, larger tires, especially like on the new AS line, are faster. So, aerodynamically, a 23-millimeter tire may be faster on like the FLO 64 AS. But when you add in the rolling resistance factor, the 28-millimeter tire is still faster. That doesn’t matter if it’s on the front or if it’s on the back. So your best option is to pick the fastest tire and you do not want to change the size of your tires. It’s kind of a myth that a lot of people believe in, but we definitely recommend to stay away from that.

Weight and Aerodynamics

Another thing people talk a lot about is weight versus aerodynamics. We’ve written a ton about this on our blog. We’ve worked with a guy named Ryan Cooper. He is a mathematical genius in the space. He’s done a lot of work with like the track teams, a lot of the pro tour teams. He developed a math model years ago that basically predicted people’s times and gave them…it’s a company called Best Bike Split, which was acquired by Training Peaks. Ryan’s been over there for a number of years. But he would basically set up the race course. He would know your FTP. And he could tell you what wattages to hold at certain places. And he could predict your times even without seeing you ride, or even following his program, he could predict your time within like seconds. The first time I saw it happen was back in the day called Josh Amberger. Ryan was kind of tweeting out these predicted times for athletes, and Josh was actually staying with us at the time. He’s like, “Man, I don’t understand how this guy’s doing this and why he thinks he knows what I’m going to ride.” And it was funny, and after the race, Josh came in and he goes, “How did that guy do that? He nailed my time perfectly.”

He uses a number of like weather stations and he gets air direction. Again, it’s some super, super smart stuff. So the reason I’m saying this is because we’ve worked with him to understand the complexities of weight and aerodynamics. Another guy in the space, a very, very respected, very, very intelligent guy named Tom Anholt has done some studies. So the importance of factors associated on some of the stuff that Tom has done, and so there’s a ratio of 60 to 1, in some cases up to 100 to 1 where aerodynamics trumps weight by a factor of 60 to 1. So it’s 60 times more important. One of the things we did with Ryan to sort of prove that was we created these models that we use his software for, and we looked at different Ironman courses. We looked at like the Alpe d’Huez which is part of the Tour de France and which one of the steepest climbs in any type of cycling. And we wanted to show that a very heavy at the time, because we have these like older wheels, the aluminum plus carbon line which are our first generation was a heavier wheelset, we used like a front 90 and a disc, which again added some more weight. So I think it was 2200 grams for the full set. And then we took a theoretical lightweight set, like an 1100-gram wheelset, which if anybody knows anything about this, that’s really difficult to do, sometimes may not even be possible.

But it just had a standard profile like an OE wheel. And so we ran the model to show…so basically, you’re doubling the weight of the wheels, but you have a much more aerodynamic profile. And no matter what course we looked at, the heavy aero set always beat the very light non-aerodynamic set. The most aggressive Ironman course in the country is a course called Savage Man. It saves over a minute on that course. Kona is six to seven minutes, which…none of this includes rolling resistance or tires either, so it’s kind of crazy. So just by using the more aerodynamic set, you save yourself a lot of time. And if you think of Kona sort of as an average course, you’re thinking six to seven minutes. So aerodynamics is extremely important.

Since that time, all of our new carbon clincher line, AS line is much, much lighter. So you’re actually getting a more improved benefit there. Even going up to the Alpe d’Huez with the new AS line versus the theoretical light set, a lot of people say they’re climbing wheels. And to be honest, it’s just not true. Aerodynamics matters at pretty much all speeds. There’s a part of the drag equation, which is the velocity component, which is squared. So the faster you go, it’s sort of an exponential growth of drag. But even at low values, one of the common myths is is that you need to be traveling a certain speed in order to gain the benefit of aerodynamics. And I’ve written a few blog articles about this as well. And the fact is it’s actually false. The slower you go, so let’s say that you’re a cyclist and your average speeds are 12 miles an hour, you actually save more time than somebody who travels at 25 miles an hour. And the reason for that is because you spend more time on the course at that speed. So you think about it’s becomes a percentage question. And so let’s say you spend 8 hours riding at 12-miles an hour, or you…let’s call it 24 to make it easier, and only spend 4 hours at 24 miles an hour for the same course. You double your time on the course. And so from an overall time savings perspective, you save more because there’s more time experienced at a slower speed. So don’t be confused that you need to be traveling like…one of the common ones I hear is like 20 plus miles an hour. That’s just not true.

And again, it just goes back to kind of debunking some of the misinformation is people look at it as if you have to be going 20 miles per hour. But that does not take into consideration the relative velocity. So it just kind of shows that that’s just a myth that doesn’t hold up too much. You may be going 20 miles an hour, you may be going 15 miles an hour, but you may have a 10-mile an hour headwind and so your relative velocity is 25 miles an hour. So again, because of that square component, it becomes more important. So make sure you consider using aero wheels for all speeds.

Most Aerodynamic Tire Sizes

Another thing a lot of people ask is, again, we talked a little bit about this is what is the most aerodynamic tire size? The truth is is that the most aerodynamic tire size is genuinely a smaller tire that has a really good interfacing with the rim. There’s a lot to talk out there about something called a rule of 105, which comes from a guy that I highly respect in this industry, Josh Portner. They did a lot of testing back in the day. They had some different profiles and things that they were doing I think back in the original Firecrest shapes. And so they saw some stuff around this rule of 105, which I’m not saying is bad, I’m not saying is even inaccurate for the tires that they were using. The stuff that we’ve used, we don’t generally see…not everything falls within the 105. Like I say, it really comes down to a balance of width and depth and over the thousands of rim shapes that we’ve optimized with. We don’t always hit that rule. I think it’s generally a good rule to follow. But like I said, the most aerodynamic tire size really generally becomes a smaller tire. The thing that kind of throws that out the window is you don’t want to think of just rolling resistance…or sorry, just aerodynamics. You have to consider rolling resistance as well, which is something that we didn’t consider until our most recent wheel line. And I’ll talk more about rolling resistance in the next one. But, yeah, so don’t consider just the most aerodynamic tire, consider the tire that is very aerodynamic. And you want to pick a wheel that’s also been optimized for rolling resistance so you have sort of a combination of things.

The Rider as the Biggest Drag Factor

Another thing that a lot of people will talk about is we talked about aerodynamics of cycling wheels, tires, pressures, and everything else. But what about aerodynamics in general for cyclists? So the biggest drag component that you’re ever going to experience on a bike is yourself, which is your body. The biggest improvement you can make from an aero perspective is to get yourself a really good fit. You can be fit by a fitter. Generally, a lot of fitters you’re going to find in shops aren’t going to really look at the aerodynamic component of it. But they may get you in an extremely comfortable, efficient position. Sometimes, people will go to a wind tunnel to get fit. You can do that. It’s a really cool experience. And what you get is you sort of get this live, real-time view of testing a number of different things. You can test, you know, different helmets, different kits, different bars, different stack height, different reach, different saddle. Everything changes, and so you get this really dynamic view of it.

I recommend that if you’re going to spend some time getting…you want to make your biggest ergonomic improvement, a really good fit is great. But one thing you want to make sure you’re not doing is you’re getting into a really, really aerodynamic position that is also really, really, really uncomfortable because you’re gonna be out on the bike for a very long time. You’re gonna be miserable. You can’t hold it. Your power efficiency goes down because you may be too closed off. So make sure you’re getting into…again, it’s kind of like our weighting algorithm. You got to think we want something that’s really aero, but we also want something that is going to be stable from a yaw torque perspective. When you’re being fit with your body, you want something that is very aero, but you also want something that is very comfortable that you can stay in for a long time and allows you to put out a good amount of power.

The next biggest improvement you can make really is a set of wheels and tires that are optimized around that. So if you’ve got a great fit and you need to make another improvement, our wheels are a really good option. So, yeah, I think that that’s definitely a good thing. Kits are really interesting to look at in a wind tunnel. When you’re talking about tires and you can change the pressure by like five psi, which is fractional from a millimeter perspective and maybe a width change, seam placement, the way that it sits on your forearm versus if there’s a bunch, the way your body shape is, everything like that has a drastic improvement. You can see like if the seams are straight, sort of right in line with your biceps, sometimes that acts as like a really good thing. Sometimes it doesn’t. Again, it’s so body-specific. Helmets are another really good example of something that is very body-specific. A helmet that is really fast on one person put on another person is slower than another one. So, again, if you really want to do some testing, I think that’s a really good option. We used a sensor for the design of the 2020 wheel line, which is the AS line in the gravel wheels. And it was a sensor from a company called Aero Lab. They do CDA NCRR testing. So CDA is the drag coefficient, so aerodynamic number, and NCRR is the coefficient of rolling resistance, which is the rolling resistance number. Most people that use that sensor are really looking at an aero fit. We kind of flipped it around and we used it to test on rolling resistance, which is really cool.

Test Your Own Aerodynamics with These Wind Tunnel Alternatives

But if you want to do something that’s more dynamic as opposed to being in a wind tunnel, you could use an AeroLab test. I know they’re starting to roll those out. There’s another guy, Jim at Aero. He’s in California. I think he uses an Alphamantis. He has a velodrome so you get like real testing. And Jim, I mean, we’ve had him on the show. Jim is just a great guy, really, really knowledgeable in the space if you want a really good fit. I really like the idea of wind tunnels. And I’m not saying they’re bad. But I do also like to see people get out and actually move around and test some things out to see how it feels. There’s some guys that are friends of ours over at Stack too. Stack has like a way to basically scan yourself and you can send some stuff into them. They can help you optimize fit, which is really cool as well.

Again, the number of variables that you see when it comes to aerodynamic testing is so high. Like I say, we always go back to trends and generalizations. And if you get too worried about aerodynamics, then you’re just wasting too much energy worrying about it. So you really want to know that you’ve taken care of things, like you’ve got yourself a good fit, you’ve got yourself a good set of wheels, you’ve got tires that really fit well, you’ve got a kit that fits well. You don’t have like any obvious things like your number is not on the front flapping around or it’s not flapping behind you. You want good clean cabling on your bikes. You don’t want crazy water bottles hanging in front to break up airflow. If you’ve taken care of all that stuff, you’re going to be 95% plus of your way to being very aerodynamically sound on a bicycle, if you’re racing or whatever you’re doing. That’s the most of it. The last 5% is really, really difficult to get to. It’s really difficult to control. The conditions for the day may be different. That’s not what you’re worrying about. That 95% is going to make you an extremely fast cyclist. I’ve always said the fastest cyclists are the most intelligent cyclists. You look at their gear, you look at their bikes, you look at their fit, everything is optimized.

And that’s really what this podcast has been about. It’s what our company is about. We look at all of those things from a wheel perspective to give you the wheel that you put on your bike with a tire, with the pressure that you don’t have to worry about it and you’re making up 95% of it so that you become one of the smartest athletes. Anyway, this was a super fun podcast for me to do. I hope I’ve answered a lot of questions about aerodynamics. I hope I’ve cleared up some myths and certain things like that. If anybody has questions, I always say you can email me directly at jon@flocycling.com. I love answering questions. You want to call me, my number is on the website as well on the contact page. I love talking through this stuff. And yeah, hope you guys enjoyed it. I can’t wait to see you for episode three, which is going to be about rolling resistance, which is super fun. And we’ll see you soon. Ride safe.

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