Most aero calculators tell you "this wheelset saves 8 watts." That's nearly useless until you see it as actual seconds on a 40 km TT. This calculator does that comparison across common setups — hoods, drops, aerobars, aero helmet, deep wheels — and adds the crosswind adjustment that a real wind usually demands.
| Setup | Effective CdA | Speed | Time | vs Hoods |
|---|
Effective CdA includes a crosswind penalty for deep-section wheels — the deeper the rim, the more sideways wind costs you. Numbers are conservative, based on published tour-magazine test data.
If someone tells you "this helmet saves 8 W at 30 km/h," the number is real but meaningless until you translate it. On a flat 40 km TT at 280 W, an 8 W saving is about 47 seconds. On a 90-minute hilly road race where you're drafting 80% of the time, it's basically nothing.
This calculator does the translation for you — at your course distance, your power, and your likely wind — and shows the time you'd save across five common setups.
Probably not exactly. Body position, clothing choice, frame design and skin-fitted vs loose jerseys all matter. The numbers here are typical mid-pack numbers from wind-tunnel tests. If you want your personal CdA, a velodrome field test or a CdA-testing service will get you within ±5%.
In a strong crosswind, deep rims can be slower than 40 mm wheels. We've modeled that — the bigger the crosswind, the more the deep-rim advantage shrinks. Above ~25 km/h crosswind at 80 mm depth, you're often better with shallower rims.
No. This is solo / TT only. On the road, you're usually in a group, and aero gear matters far less than getting into the right wheels.
No. A clean calculation of time saved by CdA change alone. If you're switching to deep wheels and they're slower to accelerate, that's a separate effect (rotational inertia) — small but non-zero on rolling courses.
This calculator was built to answer a question most online versions skip or oversimplify. It runs entirely in your browser; no inputs are stored or transmitted. The math is grounded in standard cycling physics and physiology models, and is suitable for hobbyist and intermediate training use. It is not a substitute for a coach, sports scientist, or professional bike-fit service.
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Children under 13 are not the intended audience.
This calculator is provided for general informational and educational purposes only. It is not medical, mechanical, or legal advice. Predicted values depend on inputs you supply and simplified physical models; real-world outcomes vary. Use at your own risk. Brand names are descriptive only and do not imply affiliation.