Enter suspension data
Use corner-level values for one spring location. The calculator blends wheel dynamics, spring geometry, preload, and coil-bind checks.
Example data table
| Corner Mass | Unsprung Mass | Ride Freq. | Motion Ratio | Angle | Geometry Rate | Wheel Rate | Static Sag | Ride Outcome |
|---|---|---|---|---|---|---|---|---|
| 320 kg | 40 kg | 1.90 Hz | 0.92 | 12° | 50.61 N/mm | 40.98 N/mm | 58.11 mm | Balanced road tune |
This sample shows a realistic corner-level setup and demonstrates how geometry, preload, and motion ratio alter wheel behavior.
Formula used
1) Sprung mass at one corner
Sprung Mass = Corner Mass − Unsprung Mass
2) Effective motion factor
Effective Factor = Motion Ratio × cos(Spring Angle)
3) Target wheel rate from ride frequency
Wheel Rate = ((2πf)² × Sprung Mass) / 1000
4) Required spring rate at the spring
Spring Rate = Wheel Rate / (Effective Factor²)
5) Helical compression spring rate from geometry
k = (G × d⁴) / (8 × D³ × n)
6) Static wheel sag and spring force
Wheel Sag = ((Sprung Load / (k × Effective Factor)) − Preload) / Effective Factor
7) Coil bind margin
Coil Bind Margin = (Free Length − Solid Height) − (Preload + Wheel Travel × Effective Factor)
8) Corrected spring shear stress
τ = Wahl Factor × (8 × Force × Mean Diameter) / (π × Wire Diameter³)
How to use this calculator
- Enter the full mass supported at one spring location.
- Enter the unsprung mass for the same corner.
- Set the desired ride frequency for comfort or sport bias.
- Enter the motion ratio and spring installation angle carefully.
- Provide travel, target sag, spring geometry, preload, and material values.
- Submit the form to compare target rates against the geometry-based rate.
- Review wheel rate, static sag, bump reserve, stress margin, and coil-bind clearance.
- Use CSV or PDF export to save the current result set.
Frequently asked questions
1) What does spring rate mean here?
Spring rate is the force needed to compress the spring one millimeter. This tool also converts that spring stiffness into wheel stiffness using motion ratio and spring angle.
2) Why is wheel rate lower than spring rate?
The wheel usually moves farther than the spring. Motion ratio and installation angle reduce the spring’s effect at the wheel, so wheel rate is commonly lower.
3) Why does ride frequency matter?
Ride frequency links stiffness to vehicle feel. Lower values usually feel softer and calmer, while higher values generally feel sharper, firmer, and more performance focused.
4) What is a good spring index?
Spring index is mean diameter divided by wire diameter. Very low values can increase stress and manufacturing difficulty, while very high values may reduce lateral stability.
5) Does preload change spring rate?
Preload does not change the spring’s actual rate. It changes installed force, ride height behavior from droop, and how much travel is available before full compression.
6) What causes coil bind risk?
Coil bind risk appears when the required compression approaches the spring’s available compression before solid height. Low free length, high preload, or large wheel travel can cause it.
7) Why is allowable shear stress needed?
Different spring materials tolerate different stresses. The allowable value gives a screening check for durability and helps estimate whether the chosen wire size is reasonable.
8) Should I trust frequency or sag more?
Use both together. Frequency controls dynamic feel, while sag controls static position within travel. A strong design usually lands in a practical band satisfying both targets.