Aero Coefficient Tool
CL from shock-pot loads · CD from coastdown
SVR AUTOSPORTAERODYNAMICS
Conditions
Shared atmospheric values for both CL and CD calculations.
ρ = — kg/m³
Lift Coefficient (CL) — Shock-Pot Method
CL Datapoints
Aero load per axle (sum L+R, N) at each test speed.
Method: sensors zeroed at rest → suspension compression during steady-state run = aero load. Each datapoint must be from a straight-line, constant-velocity window.
| # | Speed (km/h) | F front (N) | F rear (N) | CL F | CL R | CL Tot | Bal %F | q (Pa) |
|---|
Avg CL Total
—
—
Avg balance %F
—%
—
Avg CL Front
—
—
Avg CL Rear
—
—
CL vs Speed
Balance %F vs Speed
Saved CL Configs
Save sweeps for different aero setups to compare deltas.
Drag Coefficient (CD) — Coastdown Method
Coastdown Parameters
Vehicle mass and rolling resistance for the drag calculation.
How it works: In neutral, coast from speed A to speed B and log elapsed time. The tool computes deceleration, subtracts rolling resistance, and back-calculates CD from the aero force at midpoint speed. Better: do 3+ coastdowns at different speeds and use the fitted CD / Crr values — a least-squares fit that doesn't need a Crr guess.
Crr typical: 0.012 street · 0.015 sport · 0.020–0.025 slicks.
Crr typical: 0.012 street · 0.015 sport · 0.020–0.025 slicks.
Coastdown Datapoints
Each row = one coastdown run (V_a → V_b, time Δt).
| # | V start (km/h) | V end (km/h) | Δt (s) | V mid | a (m/s²) | F tot (N) | F aero (N) | CD | CD·A |
|---|
Avg CD (assumed Crr)
—
—
Avg CD·A (m²)
—
—
Fitted CD (regression)
—
needs ≥ 2 points
Fitted Crr (regression)
—
—
L/D (avg CL / fitted CD)
—
higher = more efficient
Aero power @ 200 km/h
—kW
P = ½·ρ·CD·A·V³
Aero power @ 250 km/h
—kW
benchmark
CD vs Speed
a vs V² (regression fit)
Reading the charts: CD vs Speed should be flat. The a vs V² chart should be a straight line; the fit gives CD (slope) and Crr (y-intercept) at once.
Saved CD Configs
Save coastdown sweeps to compare aero / setup changes.
Formulas
Reference equations.
Atmospheric
P_sat: 610.78·exp(17.27·T/(T+237.3)) [Pa]
Humid air ρ: (P_atm−P_v)/(R_d·T_K)+P_v/(R_v·T_K)
Dynamic pressure: q = ½·ρ·V²
Lift (CL)
Per axle: CL = F_aero/(q·A); Total = CL_F+CL_R; Bal = CL_F/CL_Tot
Drag (CD) — coastdown
Decel: a = (V_a−V_b)/Δt
F_total: m·a; F_roll = Crr·m·g (+driveline); F_aero = F_total−F_roll
CD: F_aero/(½·ρ·V_mid²·A)
Regression: a = (½·ρ·CD·A/m)·V² + Crr·g → slope→CD, intercept→Crr
SVR Aero Coefficient Tool — SVR Autosport