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Your Aero Savings
Baseline Parameters
Baseline power is whatever you set. Speeds are solved from physics — there is no auto-targeting to 40.0 km/h.
Physics Model (flat, steady-state)
We solve cyclist speed from the steady-state power balance on flat ground:
P = 0.5 · ρ · CdA · v³ + Crr · m · g · v. Aerodynamic power scales with
v³ while rolling scales with v. At a fixed speed, watts saved by a
CdA reduction are ΔP = 0.5 · ρ · ΔCdA · v³. “Speeds” shown are solved, not forced,
given your baseline power, mass, rolling resistance and air density.
What “Baseline CdA” means here
Baseline CdA is your personal drag area in the hoods wearing normal road kit (no aero extras). It reflects size, posture, flexibility, bar width, bar height/reach, and how tidy your frontal area is. Typical ranges: Recreational ~0.32–0.38; Trained club ~0.29–0.32; Small/elite morphology ~0.26–0.29. We keep the baseline input bounded to ≥ 0.260 m² to reflect a realistic floor for “hoods/no-aero”.
How to set your Baseline CdA
- Morphology quick estimate — height/weight/shoulders + posture & mobility. Good when you’ve never tested or conditions are noisy.
- Out-&-back field test — ride both directions on flat road, steady power. Solve CdA per leg and average. Great when wind is mild and equipment/power is calibrated.
- Blend — use the slider to weight “today’s test” vs. your physiological baseline. Trust field testing more on calm, repeatable days with CdA_out ≈ CdA_back (within ~0.005–0.01). Trust morphology more when gusty, posture/kit differed, power looks off, or out/back disagree (>~0.015).
Stacking gains without double-counting (saturation)
Aero changes don’t add linearly. Tight elbows plus an aero helmet plus a skinsuit target overlapping flow structures. We use a smooth, morphology-aware saturation curve so stacked items asymptotically approach a realistic floor for the rider, instead of subtracting forever. This lets aggressive setups get fast without spitting out comic-book CdAs.
- Floor (feasible bound): A small, very well-positioned rider starting at 0.260 in hoods can reach ~0.165 with “Max Aero” + World-Class integration. Bigger/upright riders map to a higher floor.
- World-Class toggle: doesn’t lower the floor — it just gets you closer to it (better integration/coordination of kit, pose, and equipment).
Position & equipment assumptions
- Arms/Torso: drops reduce CdA vs hoods; “aero drops” ( elbows tucked, torso lower ) beat standard drops; “aero hoods” (forearms parallel, narrow) beat both, within UCI rules.
- Head: a stable tucked head helps, but only if you can hold it without compromising control.
- Wheels: deeper front typically yields larger aero benefit than deeper rear for road use; rear disc is best in pure aero but not always race-legal/ride-friendly for road.
- Bottles: placement matters: between-the-arms (BTA) / behind-saddle / shaped bottles generally beat two round bottles on frame; “no bottles” is fastest but impractical.
- Helmets & clothing: aero road < TT helmets < best-match TT with good head control; tight skinsuits usually beat jerseys; hair removal and aero socks/overshoes can be small positives.
Inputs & defaults
- ρ (air density): default 1.225 kg·m⁻³ (sea level, ~15 °C). Lower at heat/altitude → faster speeds for same watts.
- Crr: default 0.004 is “decent race tire on good tarmac.” Use 0.003–0.0035 for top tubeless race setups, 0.005–0.006 for rough roads/commute rubber.
- Mass: system mass (rider + bike + bottles, etc.).
- Power: use net crank/hub power. If your meter over-reads, your solved speeds will be optimistic.
Limitations & good practice
- Field tests: use steady laps, repeat in both directions, similar posture/kit, and calibrate equipment. Average multiple passes.
- Yaw sensitivity: the model reports at effective 0–low yaw; gusts and wheel/helmet shape interactions can push results either way.
- Individual variation: integration quality (how kit + pose + frame interact) is huge. Treat outputs as planning-grade, not lab-grade.
This is a planning tool tuned to typical magnitudes from public tunnel/CFD reports and validated field-testing methods. Real gains depend on your morphology, fit discipline, yaw environment and how cleanly your choices integrate.