Calculator Inputs
Formula Used
Sprung corner weight = Corner weight − Unsprung weight
Effective displacement ratio = Motion ratio × cos(shock angle)
Wheel rate = Spring rate × Effective displacement ratio²
Ride frequency = (1 ÷ 2π) × √((wheel rate × 386.09) ÷ sprung corner weight)
Required spring rate = Target wheel rate ÷ Effective displacement ratio²
Wheel sag = Sprung corner weight ÷ Wheel rate
Set the shock angle to zero when your measured motion ratio already includes angle effects.
How To Use This Calculator
- Measure the corner weight on scales with the vehicle ready to drive.
- Estimate or measure unsprung weight for that corner.
- Enter motion ratio as shock movement divided by wheel movement.
- Enter the shock angle measured from the wheel travel direction.
- Select the solving method that matches your tuning goal.
- Compare the required spring with your current spring.
- Review sag, preload, travel margin, and setup warnings.
- Export the result for your build notes.
Example Data Table
| Use Case | Corner Weight | Unsprung Weight | Motion Ratio | Angle | Target Frequency | Suggested Spring |
|---|---|---|---|---|---|---|
| Street front | 725 lb | 85 lb | 0.88 | 8 degrees | 1.50 Hz | 325 lb/in |
| Sport front | 760 lb | 90 lb | 0.84 | 12 degrees | 1.90 Hz | 600 lb/in |
| Track rear | 690 lb | 80 lb | 0.78 | 15 degrees | 2.30 Hz | 950 lb/in |
Understanding QA1 Spring Choices
A spring rate decision starts with load, leverage, and travel. The calculator joins those values. It helps builders compare a real spring with a target rate. It also shows the wheel rate, which is the rate felt at the tire. That value matters because the tire does not always move the same distance as the coilover.
Why Motion Ratio Matters
Many suspension layouts place the coilover inboard or at an angle. This changes the force and movement reaching the wheel. A low motion ratio can make a stiff spring feel softer at the tire. A large angle can do the same. For that reason, spring rate alone can mislead a setup choice. Always measure shock travel and wheel travel carefully before choosing parts.
Using Ride Frequency
Ride frequency gives another way to judge the result. Lower values usually feel softer. Higher values usually feel firmer and more responsive. Street cars often need comfort and usable travel. Track cars may accept a higher frequency for sharper control. This tool uses the sprung corner weight, not the full corner weight, because tires, wheels, brakes, and other unsprung parts are not supported in the same way.
Checking Compression And Preload
Static compression helps show how much spring movement is used at ride height. Too much compression can reduce bump travel. Too little compression can create poor droop balance. Preload is useful for setting installed height, but it should not be used to hide a poor rate choice. Large preload can hold the suspension near top-out and reduce grip.
Practical Setup Notes
Use the output as a planning guide. Then verify the car on scales. Check actual ride height after installation. Recheck corner weights after alignment. Suspension bushings, shock gas pressure, sway bars, and tire stiffness can change the final feel. Small changes are best. Compare one spring step at a time. Record every change with notes. This makes later tuning easier and safer.
Final Thoughts
A good QA1 style setup balances comfort, control, and travel. The best spring is not always the stiffest one. It is the spring that places the suspension in the right working range. Use clean measurements, review warnings, and confirm the result with road testing.
FAQs
1. What is a QA1 spring rate?
It is the spring stiffness used with a QA1 style coilover or spring setup. The value is usually shown in pounds per inch.
2. What does wheel rate mean?
Wheel rate is the effective spring stiffness at the tire. It changes with motion ratio and shock angle.
3. Why is motion ratio important?
Motion ratio shows how much the shock moves compared with the wheel. A lower value reduces effective wheel rate.
4. Should I use full vehicle weight?
No. Use corner weight for one wheel position. Then subtract unsprung weight to estimate sprung corner weight.
5. What ride frequency is best?
There is no single best value. Softer street setups use lower values. Firmer track setups often use higher values.
6. Does preload change spring rate?
Preload does not change the spring rate. It changes installed load and ride height behavior before movement begins.
7. Why enter shock angle?
Shock angle reduces effective wheel rate when it is not included in the measured motion ratio. Set it to zero if already included.
8. Is this a final suspension recommendation?
No. Use it as an estimate. Always confirm fitment, travel, handling, alignment, and manufacturer guidance before final installation.