Spring Ride Height Calculator

Model suspension sag, perch changes, and wheel movement. Review outputs instantly and download result records. Improve setup decisions using clear engineering calculations and graphs.

Calculator Inputs

Use spring travel divided by wheel travel.
Use positive values to raise predicted ride height.
Reset

Example Data Table

System Free Length Spring Rate Corner Weight Unsprung Weight Motion Ratio Reference Height Perch Adjustment Estimated Ride Height
Metric 220 mm 70 N/mm 360 kg 40 kg 0.92 150 mm 6 mm 103.55 mm
Imperial 10.00 in 450 lb/in 900 lb 90 lb 0.88 6.50 in 0.25 in 4.45 in

Formula Used

1. Sprung Corner Load = Corner Weight − Unsprung Weight

2. Spring Force = Sprung Load ÷ Motion Ratio

3. Spring Compression = Spring Force ÷ Spring Rate

4. Wheel Deflection = Spring Compression ÷ Motion Ratio

5. Wheel Rate = Spring Rate × Motion Ratio²

6. Static Ride Height = Reference Ride Height − Wheel Deflection + (Perch Adjustment ÷ Motion Ratio)

7. Natural Frequency = (1 ÷ 2π) × √(Wheel Rate ÷ Sprung Mass)

The motion ratio in this file is defined as spring travel divided by wheel travel. The tool converts values internally so the equations stay consistent in both systems.

How to Use This Calculator

  1. Select metric or imperial units before entering data.
  2. Enter the spring free length and spring rate.
  3. Enter the measured corner weight and the unsprung share.
  4. Type the motion ratio using spring travel divided by wheel travel.
  5. Enter the reference ride height you want to compare against.
  6. Enter perch adjustment. Positive values raise the predicted ride height.
  7. Press the calculate button to show results above the form.
  8. Use the CSV or PDF buttons to keep a setup record.

FAQs

1. What is motion ratio in this calculator?

It is spring travel divided by wheel travel. A smaller ratio means the wheel moves more than the spring. That increases wheel deflection for the same spring rate.

2. Why do I subtract unsprung weight?

The spring mainly supports the sprung portion of the corner. Tires, hubs, and part of the control assembly are unsprung. Removing that share improves the static estimate.

3. Does preload always change ride height?

Not always. Simple preload without seat movement mainly changes initial force. Threaded perch movement changes installed position, so it changes ride height more directly.

4. What is wheel rate?

Wheel rate is the effective rate seen at the wheel after motion ratio is applied. It is lower than spring rate when the suspension does not move one-to-one.

5. Can I use this for coilovers and separate spring setups?

Yes. The key is using the correct motion ratio for the spring location. Coilovers often have a higher ratio than springs mounted farther inboard.

6. Why is my predicted ride height lower than expected?

Common causes are an incorrect motion ratio, an underestimated unsprung share, a soft spring, or a reference ride height that was measured from a different baseline.

7. What does natural frequency tell me?

It estimates how quickly the sprung corner responds to bumps. Higher values usually feel firmer. Lower values often feel softer and more comfort focused.

8. Can this replace full suspension setup work?

No. It is a strong planning tool, but alignment, damper tuning, corner balancing, tire stiffness, and bushing compliance still affect the final real-world ride height.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.