A cyclocross race bike, built from code

Ciklobike by DarwinAI is a free, browser-based 3D emulator of a professional cyclocross race bike. Every part is generated from code based on technical specifications: the carbon frame, the Shimano GRX Di2 12-speed drivetrain, hydraulic disc brakes, wheels, spokes, tyres, chain, pedals, cockpit, seatpost and saddle. You can pedal, shift, brake, explode it, inspect it in X-ray and blueprint modes, and resize it. Nothing to install, and it works in Hungarian and English.

No, it is an emulator. It reproduces how a cyclocross bike works and fits together: the cranks drive the chain, cassette and rear wheel, shifting moves the derailleur, and the brake stops the wheel. It uses simplified but plausible motion and does not calculate full physics such as tyre grip, aerodynamics or rider power.

Procedurally. Functions and parameters (tube profiles, tooth counts, chain pitch, spoke patterns, rotor diameters) build each component from public technical specifications, drawings and manufacturer illustrations, not from scanned or downloaded meshes. That is why parts move independently, separate in the exploded view, and resize when you change frame size, crank length or stem length.

A cyclocross (CX) bike is a drop-bar race bike for short, intense races (about an hour for elites) on laps of grass, mud, sand, stairs and barriers, where riders often dismount and run. Compared with a gravel bike it steers more quickly and has a shorter wheelbase, a higher bottom bracket and a lighter build. Its clearance is sized around the 33 mm UCI tyre limit plus room for mud, and it usually lacks luggage mounts. Gravel bikes take wider tyres (often 40 mm or more), with more stable, relaxed geometry and wider gear ranges.

UCI equipment rule 1.3.018 says that in cyclo-cross a tyre may not be wider than 33 mm, measured at its widest point, and may not carry spikes or studs. The limit was introduced in 2010, in the same rule update that allowed disc brakes in cyclocross. It applies to UCI-sanctioned races, and many national and amateur series follow it too. Ciklobike shows a warning when you fit a wider tyre.

Di2 (Digital Integrated Intelligence) replaces shift cables with electronic signals. Press a shift button and a small motor in the derailleur moves the chain to the next cog, with the same precision every time. In Shimano’s 12-speed GRX RX825 Di2 groupset, launched in 2024, the shift levers are wireless and run on coin-cell batteries. The derailleurs share one internal rechargeable battery, charged through a port on the rear derailleur. In Ciklobike you can shift while pedalling and watch the chain step across the cassette.

Pulling the lever pushes a piston in the lever’s master cylinder. The incompressible fluid (Shimano uses mineral oil) carries that pressure through the hose to the caliper pistons, which clamp the pads onto a rotor fixed to the hub. The caliper pistons are larger than the lever piston, so a light finger force becomes a strong, controllable clamping force that stays consistent in mud and rain. In Ciklobike, if the wheels are spinning and you pull the brake lever, the rotor and wheel slow down and stop.

No. It is a visual guide, not a fitting. You can change frame size, crank length, stem length, saddle height and saddle setback and see how the crash-test dummy’s posture changes while pedalling. Before buying, compare stack and reach on the manufacturer’s geometry chart. A common starting point for saddle height is inseam × 0.883, measured from the bottom-bracket centre to the top of the saddle (the LeMond method). For pain, injury or racing goals, see a qualified bike fitter.

The exploded view pulls every individual part apart along its assembly direction: frame, fork, wheels, spokes, tyres, cassette cogs, chain links, crankset, pedals, brakes, cockpit, seatpost and saddle. You see what each part is and where it goes, and one press reassembles it. X-ray mode makes the outer shells see-through to show what sits beneath, and blueprint mode renders the bike as a dimensioned technical drawing.

It runs on desktops, laptops, tablets and phones in a browser with WebGL2 (current Chrome, Edge, Firefox and Safari all qualify). On weaker devices it renders with less detail; if the browser does not support WebGL2, the app says so clearly. Ciklobike is an installable web app: once you have opened the emulator, it also starts without a connection.

No. There is no sign-up and the site uses no cookies. Visits are measured with cookieless, aggregate Umami statistics (for example, how many people started the emulator) that do not identify visitors. Settings such as the language stay on your device. The privacy notice has the details.

No. Ciklobike is an independent educational project designed and developed by DarwinAI. Shimano, GRX and Di2 are trademarks of Shimano Inc. They appear only to identify the real-world components the model is based on. UCI rules are cited for information.