Hold the Wheel

CodeUX.design

About this app

Hold the Wheel is a cycling physics sandbox, not a game. There is no winning and no score. You configure a rider, clone yourself with a different mass or height, put one of you on the other’s wheel, and watch what each version has to do as the road tilts up and down.

WHAT IT SHOWS

On the flat at 45 km/h, aerodynamic drag is 80-85% of the power demand. Mass barely enters, drafting is a multiplier on your drag area rather than a flat saving in watts, and the limit is the lighter rider's absolute power.

On a 6% climb at 20 km/h that aero term has collapsed by a factor of (20/45) cubed, gravity dominates, and watts per kilogram of total mass rules instead.

The grade where those two swap is the single most informative number here, and it moves with speed: around 0.5% at 21 km/h, around 3.2% at 43 km/h. At the speeds a group ride actually takes a roller, nearly every rise favors the lighter rider. That is the intuition this is built to give you.

HOW IT MODELS RIDERS

Nothing here is a free parameter you can set to a flattering number:

- Drag area is derived from height and mass through Du Bois body surface area, so a taller rider pays for the height.
- Critical power scales with mass to the power 0.67, not linearly, so holding watts per kilogram constant across masses does not quietly make the heavy rider superhuman.
- Anaerobic reserve scales roughly linearly with mass, which is what makes repeated rolling terrain accumulate a real cost rather than washing out.
- Drafting reduces drag area, so its benefit falls away on a climb exactly as it does for a real rider.
- Kinetic energy traded for height cancels mass, and so does rolling resistance. Only aerodynamics breaks the symmetry between riders. If a result seems to favor the heavy rider through inertia alone, it is the model being honest, not a thumb on the scale.

BUILD THE COURSE

Lay out a course segment by segment - lengths and grades you choose - and read off where each rider gains and loses. The whole run is computed up front, so you can jump to any point on the elevation profile and inspect it rather than waiting to arrive.

SOLVED ON YOUR PHONE

There is no server working any of this out. The whole run is computed on the device before you press play, which is what lets you tap anywhere on the elevation profile and arrive there instantly instead of waiting to ride to it. It also means a tunnel, an airplane or a mountain pass with no reception makes no difference to it. Your riders and courses are saved on the device, so they are there when you come back.

What’s new

Initial release 🚀