Why would I get carbon wheels?
Carbon wheels are a great upgrade to your bike, which will have most likely come to you with aluminium wheels as standard. Carbon is lighter and stiffer than aluminium, meaning the following:
For the same rim depth as aluminium, the carbon wheel will weigh less.
The lightweight property of carbon allows wheels to have deeper rims. Deeper rims will make your bike more aerodynamic.
A stiffer carbon wheelset will feel more responsive compared with your aluminium wheelset.
Also… carbon wheels look MEAN!
Why do aerodynamics matter?
Aerodynamics refers to the way air flows around solid, moving objects. As we all know from cycling headlong into a headwind, the better you slice through the air, the easier life feels. You can improve your ‘slicing’ ability in numerous ways, from the clothes you wear, to the position you hold, to the shape of the helmet on your head. It’s a pretty complex subject, so we won’t attempt to nail down everything; however, we’ll try to enlighten you on the basic concepts.
What is drag?
The force you’re always cycling against is wind resistance (drag); the higher the wind resistance, the greater the energy required to move through it.
There are two types of drag:
Pressure drag – As layers of compressed air particles hit the front of you they ‘stick’ to your surfaces, flow around them and then become separated, and begin to swirl and spread out behind you, creating a low-pressure zone and turbulent flow: A drag force.
Skin friction drag – Sounds painful and a bit gross, but actually it’s just air particles colliding with the rough surface that is you. As the air particles get nearer to the uneven surface they slow down (and, in turn, slow down the particles around them). The particles that actually touch the surface come to a complete stop. All of this creates friction and impedes forward movement.
Annoyingly, the faster you go, the more wind resistance you build up, so that’s where being aerodynamically efficient becomes critical.
What is the yaw angle?
Imagine you’re riding due north on a calm sunny day, forging forwards along the road without a care in the world. By cycling forwards, you’re creating your own headwind, forcing your long plait to flow out behind you in a straight line, pointing exactly due south. Suddenly a gust of wind blows in from the west, blowing your plait eastward. The angle created, between where your plait now is and where your plait was, is the yaw angle!
Of course, when you’re pedalling away throughout the day, the wind will change direction and speed, and you will accelerate and decelerate numerous times, constantly altering the yaw angle. As you accelerate, you reduce the yaw angle. As the wind picks up, the yaw angle increases.
Why does having deeper rims make my wheel more aerodynamic?
The smooth airfoil shape (a rounded leading edge, followed by a sharp trailing edge – a sort of sideways teardrop) of deep-section wheels mean they pass through the air a lot more cleanly than a box-section rim (what you find on an aluminium clincher). The tyre is the leading edge that splits the air and then the deep rim controls the airflow, helping it to come together again smoothly, reducing the amount of turbulent air, which causes drag. A shallow box-section rim can’t control the airflow in this way, meaning there’s more drag.
Furthermore, deep-section wheels aim to ‘sail’ on crosswinds by forcing the airflow to follow the shape of the wheel. As the crosswind passes over the wheel at an angle, forward thrust is created; therefore, as the wind angle increases the wheels’ own drag decreases.
There’s a point, however, at which the airflow detaches, which causes turbulence, an area of low pressure behind the rim and a sharp increase in drag. This is the ‘stall’ point. The deeper the rims the higher the stall angles. Yay!
I want to know MORE
Dov, the founder of Parcours wheels, travelled to North Carolina to have his wheels aerodynamically tested in a wind tunnel. Check out the ‘Technical’ section on the website for detailed findings: https://www.parcours.cc/pages/aerodynamics-1