🚴 Bike Comparison

This tool estimates how much power you would need to maintain the same speed on a different bike setup in Zwift. It replays your actual ride data — your speed, gradient, and drafting at every second — through a physics model and calculates what your power output would have been if you were on a different frame and wheelset. A lower Normalized Power means the bike is more efficient (you'd need less effort to go the same speed).

The telemetry is your actual ride timeline from Zwift — either fetched via the Zwift API using an activity ID, or parsed from a .fit file you export from Zwift. It includes second-by-second data points for speed, power, gradient, altitude, cadence, and heart rate.

Bike performance data (aerodynamic drag coefficient and rolling weight for every frame, wheelset, and upgrade level) comes from ZwifterBikes, which measures these values through controlled in-game speed tests. The physics model used to convert bike stats into power estimates is documented on their How It Works page.

Cd (Drag Coefficient) represents how aerodynamic a bike is in Zwift's physics engine. A lower Cd means less air resistance, which matters most on flat roads and at higher speeds. The total aerodynamic drag depends on both the bike's Cd and the rider's frontal area (estimated from height and weight).

Bike weight affects climbing speed — lighter bikes require less power to go uphill. On flat terrain, weight has almost no effect. As a rule of thumb: prioritize low Cd for flat or rolling courses, and low weight for hilly or mountainous courses.

Normalized Power is a way of measuring effort that accounts for the variability of cycling power. Unlike average power, which simply averages all your power readings, NP gives extra weight to hard efforts and surges.

The calculation takes a 30-second rolling average of power, raises each value to the 4th power, averages those, and then takes the 4th root. This means a ride with lots of sprints and coasting will have a higher NP than average power, while a steady ride will have NP very close to average power.

NP is the primary metric used in the comparison because it better represents the physiological cost of a ride. If a bike change gives you a lower NP for the same speed, it means the ride would feel easier overall.

The chart plots three lines over the duration of the ride:

• Actual Bike — the power needed on your selected actual setup.
• Alternative Bike — the power needed on the comparison setup to maintain the same speed.
• Est. Draft Savings (dashed) — the estimated power saved by drafting at each moment. This is inferred by comparing your recorded power to what solo power would be at that speed and gradient. It helps visualize how much benefit you got from the pack.

There are a few things to keep in mind:

• Bike not recorded: Zwift's telemetry does not include which bike you actually used. You need to select your "Actual Bike" manually.
• Height and weight are current values: When fetching via the API, we pull the current in-game height and weight from the rider's profile, not the values at the time of the ride. If these have changed since the ride, the estimates will be slightly off. When loading from a .fit file, these values will stay as the defaults.
• Drafting is estimated: The telemetry doesn't explicitly record draft status. Instead, the tool infers a draft factor by comparing your actual power to what solo power would be at that speed and gradient. This estimate is then applied equally to the alternative bike, but it may not perfectly capture complex pack dynamics.
• Powerups not tracked: Zwift powerups (aero boost, lightweight, draft boost, etc.) are not recorded in the telemetry, so their effects can't be accounted for in the comparison.
• Assumes same speed: The comparison asks "what power would I need to go the same speed on a different bike?" It would be interesting to also calculate "what speed would I get for the same power?", but that's difficult to answer because it depends on interactions with other riders.

Some frames and wheels in Zwift can't be purchased in the Drop Shop — they require completing challenges (e.g. the Tron bike from the Everest challenge), winning event prizes (e.g. Big Spin wheels), or spinning the prize wheel atop Alpe du Zwift (Lightweight Meilenstein wheels). Checking "Exclude special unlocks" hides these from the best bikes search so you only see equipment you can buy directly. Default starter equipment (like the Zwift Steel frame and Classic wheels) is not affected.

A bike is Pareto optimal if no other bike is better in both aerodynamics and weight simultaneously. For example, a bike with the best Cd but moderate weight is Pareto optimal because nothing else beats it on aero without being heavier. Enabling the Pareto filter narrows the search to only these "best trade-off" bikes, which dramatically reduces the number of combinations to test and focuses on setups that aren't strictly outclassed.

The time range slider lets you select which portion of your ride to analyze. By default, it auto-trims the cooldown period (the slow-down at the end of a race) since that segment doesn't represent real racing effort. You can also use it to focus on a specific climb, sprint, or section of the course.

Your activity ID is in the URL when you view a ride on zwift.com. Go to your activity feed, click on a ride, and the long number in the URL is your activity ID (e.g. zwift.com/activity/1234567890). Alternatively, you can export a .fit file from the Zwift companion app or from your Zwift.com activity page and upload it directly — no login required.