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Ride Height Calculator

Calculate ride height changes from perch adjustments and spring rate swaps.

Ride height is not a standardized measurement — it can be taken from the rocker panel to the ground, the fender lip to the ground, or any other repeatable reference point. We recommend measuring from the center of the wheel straight up vertically to the fender lip. This removes wheel and tire diameter from the equation, making the measurement consistent across different wheel and tire combinations and comparable from setup to setup.

These calculators are designed to get you close and reduce the number of trial-and-error iterations — they will not be perfect down to the millimeter. Real-world factors like friction in the suspension system, the secondary spring rate of control arm bushings, and the sum of manufacturing tolerances across all components will cause small deviations from the calculated values. Always roll the car forward and backward several times to settle the suspension before measuring ride height.

Vehicle Parameter Lookup

Select your vehicle to see factory motion ratios and axle weights. Use these as reference values in the calculators below.

About This Data

Axle Weights are factory-published values divided by two to approximate per-corner weight. These do not account for options, modifications, or actual weight distribution. When a calculator requires corner sprung weight, you must subtract your vehicle's unsprung mass from the per-corner value. Unsprung mass includes the wheel, tire, brake assembly, spindle/hub, and portions of the shock absorber and control arms. This data is vehicle-specific and impractical to catalog — for most passenger cars and sports cars, a reasonable estimate is 80–100 lbs (36–45 kg) per corner.

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.

Adjust Ride Height — Same Spring

Move the spring perch up or down on a coilover and see how ride height changes at the wheel. This is the most common ride height adjustment — no spring change needed.

This calculator does not require vehicle weight because the spring rate isn't changing. When you move the perch, you're simply repositioning where the spring sits on the shock body. The spring compresses the same amount under the same load — you're just shifting the entire assembly up or down. The only factor that converts perch movement into ride height change is the motion ratio, which accounts for the geometry between the shock and the wheel.

Front

Ratio of spring travel to wheel travel for the front axle. Typically 0.5 to 1.0. Use the vehicle lookup above for factory values, or check your coilover manufacturer's specs.
Measure from the center of the wheel hub to the fender lip, or use your preferred reference point. Be consistent with your measurement location.
Measure from a fixed reference point on the shock body to the top of the spring perch (adjuster collar). Record this before making changes.
The target perch position. A higher number (perch moved up) raises the car; a lower number (perch moved down) lowers it.
Perch Change
Ride Height Change
New Ride Height

Rear

Rear axle motion ratio — often different from the front. Strut suspensions are typically higher (~0.9) while multi-link or double-wishbone can be lower (~0.55–0.8).
Use the same measurement method as the front — hub center to fender lip or your chosen reference point.
Current rear perch position, measured from the same reference point on the shock body as the front.
Target rear perch position. The ride height change accounts for the rear motion ratio, which may differ from the front.
Perch Change
Ride Height Change
New Ride Height

Change Spring Rate — Maintain Ride Height

Swapping to a different spring rate changes how much the spring compresses under the car's weight, which shifts ride height. This calculator tells you how much to adjust the perch to compensate and maintain your current ride height.

Select the units that match your data before entering values. Corner sprung weight and spring rate must use the same unit system — mixing lbs with N/mm or kg with lbs/in will produce incorrect results. If your spring is labeled in lbs/in (common in the US), select lbs/in. If labeled in N/mm or kg/mm (common in Europe and Asia), select N/mm.

Front

Weight supported by one front spring. Start with front axle weight ÷ 2, then subtract unsprung mass (wheel, tire, brake, hub — typically 80–120 lbs per corner). The vehicle lookup above shows factory axle weights.
Same spring motion ratio as Section 1. This converts between spring deflection at the shock and ride height change at the wheel.
Rate of the spring currently installed. Check the spring markings, spec sheet, or product listing. This is the spring rate, not the wheel rate.
Rate of the replacement spring. A stiffer spring deflects less, raising the car. A softer spring deflects more, lowering it.
Current Spring Deflection
New Spring Deflection
RH Change (no perch adjust)
Perch Adjust to Maintain RH

Rear

Weight supported by one rear spring. Rear axle weight ÷ 2, minus unsprung mass. Rear corners are usually lighter than fronts on front-engine cars.
Rear spring motion ratio. Multi-link and double-wishbone rears typically have lower ratios than MacPherson strut fronts.
Rate of the rear spring currently installed.
Rate of the replacement rear spring.
Current Spring Deflection
New Spring Deflection
RH Change (no perch adjust)
Perch Adjust to Maintain RH
Terminology & Formulas

Motion Ratio (MR) — Ratio of spring travel to wheel travel. An MR of 0.95 means 10 mm of wheel travel compresses the spring 9.5 mm. Determined by suspension geometry — the angle and lever arm between the spring/damper and the wheel. MacPherson struts typically have high MRs (0.9+), while multi-link and double-wishbone rears are lower (0.5–0.8).

Wheel Rate — Effective spring rate at the wheel: spring_rate × MR². This is the rate the tire actually "sees." A 10 N/mm spring with a 0.7 MR produces a 4.9 N/mm wheel rate.

Spring Perch — Adjustable collar on the coilover body that sets spring preload and ride height. Raising the perch preloads the spring and raises the car. Lowering it does the opposite. Most coilovers use a threaded body with a locking ring.

Static Deflection — How much the spring compresses under the vehicle's static weight at rest. A stiffer spring has less static deflection, so the car sits higher. A softer spring has more deflection, so it sits lower.

Corner Sprung Weight — Weight supported by one spring. Total corner weight minus unsprung mass (wheel, tire, brake assembly, hub, half of control arms). Typically the unsprung mass is 80–120 lbs (36–55 kg) per corner for a road car.

Ride Height Change from Perch Adjustment:

ride_height_change = perch_change / MR
new_ride_height = current_ride_height + ride_height_change

Perch Adjustment for Spring Rate Change:

spring_deflection = corner_weight / (spring_rate × MR²) / MR
perch_adjustment = new_deflection − old_deflection