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Shock Travel Analysis

Visualize how your shock stroke is distributed between rebound and compression, and where the bump stop engages.

At ride height, the shock shaft sits somewhere between full extension and full compression. How the stroke is divided between rebound and compression travel determines how the car behaves over bumps and dips. Too little rebound travel means the wheel can't follow the road surface downward into dips. Too little compression travel means the shock bottoms out under hard cornering or bumps. A good starting point is to have the ride position in the middle third of the stroke.

Two calculators are provided below. Measure at the Shock is for when you have direct access to the shock shaft — either on a lift or with the shock removed. Measure at the Wheel is for when the car is on the ground and you cannot see the shock shaft directly — it uses fender-to-wheel measurements and the motion ratio to determine where the shock sits within its stroke.

Vehicle Parameter Lookup

Select your vehicle to see factory shock motion ratios. Use these in the calculators below to convert between shock travel and wheel travel.

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.

Measure at the Shock

Enter the shock's measurements directly. Use this when you can see the shock shaft — either with the car on a lift or with the shock removed.

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

Front

Total stroke from full extension to full compression (metal-to-metal). Found on the shock's spec sheet.
How far the shaft has compressed from full extension at ride height. Measure the exposed shaft length at ride height, then at full extension — the difference is your ride position. This value equals your available rebound travel.
Uncompressed height of the bump stop rubber or foam. The bump stop provides progressive resistance near the end of compression. Leave blank if your setup does not use a bump stop.
If provided, results will include the equivalent wheel travel.
Rebound Travel
Free Compression
Position Check

Rear

Total shock stroke metal-to-metal from spec sheet.
Distance from full extension at ride height. Equals your available rebound travel.
Uncompressed bump stop height. Leave blank if not using a bump stop.
Rear shock motion ratio for wheel travel conversion.
Rebound Travel
Free Compression
Position Check

Measure at the Wheel

Use this when the car is on the ground and you cannot see the shock shaft. This calculator uses fender-to-wheel measurements and the motion ratio to determine where the shock sits within its stroke.

You will still need the shock stroke from the manufacturer's spec sheet — this is a physical property of the shock that does not change once installed. The fender measurements combined with the motion ratio tell us how far the shock has compressed from full extension at ride height.

Enter all lengths in the same unit. The fender-to-wheel measurements and the shock stroke 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.
Total shock stroke metal-to-metal from the manufacturer's spec sheet.
Uncompressed bump stop height from specs. Leave blank if not using a bump stop.
Required for this calculator. The shock motion ratio converts between wheel travel and shock shaft travel.
Calculated Ride Position
Rebound / Compression Split
Position Check

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.
Total shock stroke metal-to-metal from spec sheet.
Uncompressed bump stop height. Leave blank if not using a bump stop.
Required. Rear shock motion ratio.
Calculated Ride Position
Rebound / Compression Split
Position Check
Terminology & Formulas

Shock Stroke (Metal-to-Metal) — The total travel of the shock shaft from full extension to full compression. This is the maximum possible stroke before internal hard parts contact.

Ride Position — How far the shock has compressed from full extension when the car is at ride height. This equals the available rebound travel.

Rebound Travel — How far the shock can extend from the ride position before reaching full extension. The wheel follows the road into dips using this travel.

Compression Travel — How far the shock can compress from the ride position before reaching full bottom-out. This travel absorbs bumps and cornering loads.

Bump Stop — A rubber or foam element inside the shock body that provides progressive resistance near the end of compression travel. It acts as a secondary spring rate that ramps up as the shock approaches bottom-out, cushioning the impact.

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

Measure at the Shock:

rebound_travel = ride_position
compression_travel = stroke − ride_position
free_compression = compression_travel − bump_stop_length
wheel_travel = shock_travel ÷ MR

Measure at the Wheel:

wheel_travel_droop_to_ride = fender_at_droop − fender_at_ride
ride_position = wheel_travel_droop_to_ride × MR
rebound_travel = ride_position
compression_travel = stroke − ride_position