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Spring Travel Analysis

Visualize how much compression travel your spring has remaining before coil bind.

A spring that reaches coil bind creates a sudden, harsh spike in rate that unsettles the car and can fatigue the spring over time. This tool shows where your spring sits within its total stroke at ride height and how much compression remains before the coils stack solid. Ideally, your shock should reach hydraulic bottom-out before your spring reaches coil bind — the shock provides a controlled stop, while coil bind does not.

Two calculators are provided below. Measure at the Spring is for when you have direct access to the spring — enter the physical measurements from the component. Measure at the Wheel is for when the car is on the ground and you cannot easily measure the spring directly — it uses fender-to-wheel measurements and the motion ratio to calculate the same results.

Vehicle Parameter Lookup

Select your vehicle to see factory motion ratios. Use the spring motion ratio in the calculators below.

About This Data

Motion Ratios are sourced from 3DM's own measurements, data shared by reputable engineering partners, or published values from the community. They represent factory suspension geometry and will change with modifications such as lowering, different control arms, or aftermarket shock mounts such as camber plates. Treat these as starting-point references, not absolute values.

Coilover vs Divorced: On a coilover, the spring is mounted on the shock body — the spring and shock share the same motion ratio. On a divorced setup, the spring is mounted separately (e.g., on a control arm) and has its own motion ratio. Use the appropriate value for your configuration.

Measure at the Spring

Enter the spring's physical measurements directly. Use this when you can see and measure the spring — either off the car or with the suspension visible on a lift.

Enter all lengths in the same unit. Results are shown in both mm and inches.

Front

The unloaded length of the spring with no force applied. Found on the spring's spec sheet or measured with the spring removed from the car.
The spring length while installed on the car at ride height. For coilovers, measure between the top and bottom perch faces. This accounts for both perch preload and static compression from the car's weight.
The minimum length of the spring when fully compressed (coil-bound). Found in the manufacturer's specs. If unavailable, stack the coils touching and measure the total height.
If provided, results will include the equivalent wheel travel. For coilovers, use the shock MR. For divorced springs, use the spring-specific MR.
Preload
Spring Stroke
Compression Remaining

Rear

Unloaded spring length from specs or direct measurement.
Spring length on the car at ride height, measured between perch faces.
Minimum spring length at coil bind from manufacturer's specs.
Rear spring motion ratio for wheel travel conversion.
Preload
Spring Stroke
Compression Remaining

Measure at the Wheel

Use this when the car is on the ground and you cannot easily measure the spring directly. This calculator uses fender-to-wheel measurements and the motion ratio to determine how much the spring has compressed at ride height, then calculates remaining travel before coil bind.

You will still need the spring's free length and block height from the manufacturer's spec sheet — those are physical properties of the spring that do not change once installed.

Enter all lengths in the same unit. The fender-to-wheel measurements and the spring specs must use the same unit.

Front

Jack the body up by the frame or subframe — not the control arm — and let the wheel hang freely at full extension. Measure the vertical distance from the bottom edge of the fender lip straight down to the center of the wheel hub. Use the same spot on the fender for all measurements.
With the car sitting on flat ground at normal ride height, roll it forward and backward a few feet to settle the suspension. Measure from the same fender reference point to the center of the wheel hub.
Unloaded spring length from the manufacturer's spec sheet.
Minimum spring length at coil bind from the manufacturer's spec sheet.
How much the spring is compressed by the perch adjuster before the car's weight is applied. If you are unsure, enter 0 — the results will slightly overestimate remaining travel, which is the less conservative direction.
Required for this calculator. For coilovers, use the shock MR. For divorced springs, use the spring-specific MR.
Calculated Installed Length
Compression Remaining
Wheel Travel to Coil Bind

Rear

Jack the body by the frame, let the wheel hang freely. Measure fender lip to center of wheel hub.
Car on flat ground, rolled to settle. Same fender reference point to center of wheel hub.
Unloaded spring length from the manufacturer's spec sheet.
Minimum spring length at coil bind from the manufacturer's spec sheet.
Perch preload. Enter 0 if unsure — results will slightly overestimate remaining travel.
Required for this calculator. Rear spring motion ratio.
Calculated Installed Length
Compression Remaining
Wheel Travel to Coil Bind
Terminology & Formulas

Free Length — The unloaded height of a spring with no force applied.

Block Height (Coil Bind) — The minimum height of a spring when fully compressed, with all coils touching. Compressing a spring to coil bind should be avoided — it creates a harsh impact and can fatigue the spring.

Preload — The amount the spring is compressed by the perch adjuster before the car's weight is applied. On a coilover, this is set by threading the lower perch up or down. Preload determines initial ride height but does not change the spring rate.

Installed Length — The length of the spring on the car at ride height, under the static load of the vehicle. This is shorter than free length by the sum of preload and static deflection from the car's weight.

Motion Ratio (MR) — The ratio of spring travel to wheel travel. Wheel travel = spring travel ÷ MR. A 0.95 MR means the wheel moves slightly more than the spring for each mm of displacement.

Measure at the Spring:

total_stroke = free_length − block_height
preload = free_length − installed_length
compression_remaining = installed_length − block_height
wheel_travel_remaining = compression_remaining ÷ MR

Measure at the Wheel:

wheel_travel_droop_to_ride = fender_at_droop − fender_at_ride
spring_compression_droop_to_ride = wheel_travel × MR
spring_at_droop = free_length − preload
installed_length = spring_at_droop − spring_compression
compression_remaining = installed_length − block_height