AtlasCalcsUtility Calculation Suite
Automotive Calculators

Suspension Motion Ratio Calculator

2026-09-27 6 min

Motion ratio from measured spring and wheel travel.

Motion Ratio
0.667
Rate Factor (MR^2)
0.444
Wheel-rate multiplier

Calculator

Spring Travel(in) Help
in

Damper shaft movement

Wheel Travel(in) Help
in

Vertical tire movement

Results update live as you type

Live statistics

Motion Ratio

0.667

Rate Factor (MR^2)

0.444

Wheel-rate multiplier

Results

Optimal

Motion Ratio

0.667

Rate Factor (MR^2)

0.444

Wheel-rate multiplier

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

Visualizations

Results overview

0.7Motion Ratio
0.4Rate Factor

Motion Ratio vs. Spring Travel

Motion Ratio

0.7
01.5

Formula

Direct travel ratio from a jack-and-measure test with the spring removed.

MR = spring travel / wheel travel

Alternative Form

Measure with springs out: jack the wheel, read damper vs wheel movement

Variables

SymbolNameUnitDescription
MRMotion ratioLeverage number

Explanation

Every spring, bar and damper calculation needs MR — measuring beats catalog values on modified suspensions.

Step-by-Step Calculation

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

Step 1

Record the inputs.

Spring Travel:2 in
Wheel Travel:3 in
Result: 2 inputs ready
Step 2

Apply the formula.

MR = spring travel / wheel travel
Result: Primary result = 0.667
Step 3

Read every derived output.

Motion Ratio:0.667
Rate Factor (MR^2):0.444
Result: Motion Ratio = 0.667
Final Answer
0.667

Worked Examples

See how the calculator works with different scenarios.

Scenario

Pushrod rear measurement.

Inputs

Spring:2 in
Wheel:3 in

Calculation

MR = 0.667; factor = 0.444

Result

0.667 motion ratio.

Interpretation

Only 44% of spring rate reaches the wheel — size accordingly.

Understanding Your Result

Your Result: Motion Ratio: 0.667

What This Means

Your suspension leverage number, measured.

Why It Matters

Unlocks correct spring, bar and damper math on any car.

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

Motion ratio is measured travel over travel.

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

  • •Measure at ride height
  • •Check bump and droop separately
  • •Rising-rate linkages change MR with travel

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.

How do I measure motion ratio?
Springs out, jack the wheel through travel, divide damper-shaft movement by wheel movement at several points.
Is motion ratio constant?
No — it varies with travel (rising-rate designs). Measure at ride height for setup math.

Related Calculators

Explore more calculators related to this topic.

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

Was This Calculator Helpful?

Page Information