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Vehicle Drag Power Calculator

2026-09-27 6 min

Total road-load drag and wheel horsepower from weight, tires, Cd, area and speed.

Total Drag
238.4 lb
Aero + rolling
Wheel Horsepower
63.6 hp

Calculator

Vehicle Weight(lb)
lb
Rolling Resistance
Drag Coefficient(Cd)
Cd
Frontal Area(sq ft)
sq ft
Speed(mph)
mph
Results update live as you type

Live statistics

Total Drag

238.4 lb

Aero + rolling

Wheel Horsepower

63.6 hp

Results

Optimal

Total Drag

238.4lb

Aero + rolling

Wheel Horsepower

63.6hp

Planning estimate from standard automotive formulas. Validate with dyno, timeslip or datalog data when precision matters.

Visualizations

Results overview

238.4Total Drag
63.6Wheel Horsepower

Wheel Horsepower vs. Vehicle Weight

Wheel Horsepower

63.6hp
0400

Formula

Complete road-load model: speed-squared aero plus weight-proportional rolling.

F = aero + weight x Crr; P = F x v / 550

Alternative Form

Rolling dominates low speed, aero dominates high — crossover ~50-70 mph

Variables

SymbolNameUnitDescription
FaAero draglbGrows with v^2
FrRolling draglbNear-constant with speed

Explanation

Two resistances with different speed laws: tires rule the city, air rules the highway — economy mods must pick their battle.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Record the inputs.

Vehicle Weight:3500 lb
Rolling Resistance:0.012
Drag Coefficient:0.32 Cd
Frontal Area:24 sq ft
Speed:100 mph
Result: 5 inputs ready
Step 2

Apply the formula.

F = aero + weight x Crr; P = F x v / 550
Result: Primary result = 63.6 hp
Step 3

Read every derived output.

Total Drag:238.4 lb
Wheel Horsepower:63.6 hp
Result: Wheel Horsepower = 63.6 hp
Final Answer
238.4

Worked Examples

See how the calculator works with different scenarios.

Scenario

Highway cruise audit.

Inputs

Weight:3,500 lb
Crr:0.012
Cd:0.32
Area:24 sq ft
Speed:100 mph

Calculation

Aero 196 + rolling 42 = 238 lb; 63.6 hp

Result

238-lb drag, ~64 wheel hp.

Interpretation

Tires 18%, air 82% — aero mods pay here.

Understanding Your Result

Your Result: Total Drag: 238.4 lb

What This Means

Total resistance and cruise power in one number.

Why It Matters

Sizes engines, predicts economy and splits mod priorities by speed.

Professional Interpretation

Treat the primary result as a planning estimate, then validate on a dyno, at the track, or with logged sensor data. If measured numbers disagree by more than ~10%, re-check inputs (units are the usual culprit) before changing parts.

Recommendations

  • •Double-check units on every input before trusting the result
  • •Compare against the worked example below to sanity-check magnitude
  • •Validate with measured data (dyno, timeslip, datalog) when it matters

Learn — fuel economy, deeply

Road load is aero plus rolling, always both.

1 · Where the gallon goes (energy path)

Engine heat

60–70% lost

Coolant + exhaust carry most energy away. Hybrids recover some via Atkinson cycle + regen.

Driveline

5–15% lost

Transmission, differential, accessories. CVTs and 8–10 speed autos lose less.

Aero drag

∝ v²

Doubles from 55→78 mph. Roof boxes hurt more than trunks.

Rolling + brakes

10–20%

Tires, weight, stops. Regen braking (hybrid/EV) reclaims city braking energy.

4 · Measure like a pro (the 3-tank protocol)

  1. Fill to first click at the same pump, record the odometer (Tank 0).
  2. Drive normally for 2–3 tanks; always refill to first click at the same pump.
  3. MPG = total miles ÷ total gallons across all tanks — averaging kills pump-click noise.
  4. Cross-check with the trip computer; a persistent >10% gap means the computer needs calibration — or the car needs service.
  5. Log with an OBD-II dongle for per-trip MPG if you want to isolate commute vs. highway behavior.

Practical Tips

  • •Pump tires for free rolling gains
  • •Aero for highway, weight for city
  • •Measure coastdown to calibrate Crr+CdA

Common Mistakes

Mixing units (inches with mm, psi with kPa)
Convert every input to the unit shown on its field before calculating.
Trusting a single output blindly
Cross-check with the worked example and, when it matters, a dyno or datalog.

Assumptions

This calculator makes the following assumptions to provide estimates:

Steady-state model: Formulas assume stabilized conditions; transients, heat soak and traction limits are excluded.
Standard factors: Empirical constants (BSFC, VE, drivetrain loss) use typical values — your combination may differ.

Limitations

Be aware of these limitations when using this calculator:

Estimate, not measurement: Predictions carry real-world scatter of roughly ±5–15% depending on the model.
No transient effects: Shift time, wheelspin, spool lag and heat soak are not modeled here.

Frequently Asked Questions

Answers to common questions about this calculator.

Aero or tires for better MPG?
City: tires and weight. Highway: aero. Match the mod to where you drive.
What Crr do my tires have?
Eco tires ~0.008-0.010; standard ~0.011-0.013; sticky/track 0.013-0.018+.

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Related Guides

Deepen your understanding with these educational resources.

Glossary

Technical terms used in mortgage calculations explained in plain language.

MPG
Miles per gallon. Distance travelled per gallon of fuel; higher is better. US gallon = 3.785 L.
L/100 km
Litres consumed per 100 kilometres; lower is better. Standard metric efficiency unit.
MPGe
Miles per gallon-equivalent. EV metric: miles travelled on 33.7 kWh (energy of 1 gal of gasoline).
CAFE
Corporate Average Fuel Economy — US fleet-average efficiency standard enforced by NHTSA.
Rolling resistance
Energy lost deforming tires as they roll. Low-pressure or wide tires raise it.
Aerodynamic drag
Air resistance growing with the square of speed — why highway MPG falls fast above 60 mph.
Hypermiling
Driving techniques (coasting, steady speed, anticipation) that maximise real-world MPG.
OBD-II
On-board diagnostics port. Scanners and dongles read live MPG, fuel trim and fault codes.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

EPA Fuel Economy Testing (40 CFR Part 600)CAFE — Corporate Average Fuel Economy Standards (NHTSA)WLTP — Worldwide Harmonised Light Vehicle Test ProcedureSAE J1321 / J1711 — Fuel consumption test proceduresISO 2575 — Road vehicles symbols & efficiency markings

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