Coil Spring Cutting Calculator
Estimate how trimming a compression or suspension coil changes active coils, spring rate, free length, loaded ride height, coil-bind clearance, and Wahl-corrected stress.
⚙Named coil cutting presets
Load a realistic spring case, then change the cut amount, active coils, wire size, motion ratio, bump travel, and stress allowance.
📏Original spring, cut, and installed load
Measured or catalog rate before cutting.
Unloaded length before trimming.
Count every visible turn from end to end.
Coils that deflect under load, excluding dead end coils.
Use decimal turns: 0.25, 0.50, 0.75, 1.00.
End shape changes how much active length is truly removed.
Used for solid height and stress checks.
Mean diameter is outside diameter minus one wire diameter.
Select the closest material for modulus and stress screen.
Used only when custom material is selected.
Use wheel corner load for vehicle springs or axial load for fixtures.
Use 1.00 for direct-acting coil springs.
Wheel bump travel to the stop or the shortest expected length.
Multiplies calculated stress for a first-pass margin check.
Closed or ground ends often keep about 1.5 to 2 inactive coils.
Cut spring results
🧪Material and spring-spec grid
📊Coil cutting reference tables
| Cut amount | Typical rate change | Free-length change | Calculator note |
|---|---|---|---|
| 0.25 coil | About 3% to 6% | Small pitch segment | Often used for careful final trimming. |
| 0.50 coil | About 7% to 14% | Half of one coil pitch | Measure ride height again before more cutting. |
| 0.75 coil | About 11% to 22% | Three-quarter pitch | Bind margin and seated end shape matter. |
| 1.00 coil | About 15% to 30% | One full coil pitch | Large rate change; check shocks, stops, and alignment. |
| 1.50 coils | About 25% to 50% | One and a half pitches | High-risk first cut unless spring data is proven. |
| Material | Shear modulus | Screen stress | Cutting concern |
|---|---|---|---|
| Music wire | 11.5 Mpsi / 79.3 GPa | High static strength | Small-diameter springs; avoid heating the end. |
| Hard drawn wire | 11.4 Mpsi / 78.6 GPa | Moderate allowance | General utility springs need conservative stress. |
| Oil tempered wire | 11.2 Mpsi / 77.2 GPa | Good for larger coils | Common automotive coil material. |
| Chrome silicon | 11.5 Mpsi / 79.3 GPa | Strong fatigue option | Still needs bind and buckling clearance. |
| 302 stainless | 10.0 Mpsi / 69.0 GPa | Lower modulus | Rate may be lower for the same geometry. |
| Phosphor bronze | 6.3 Mpsi / 43.4 GPa | Lower stress range | Use only with verified material limits. |
| Suspension input | What it means | Formula use | Common range |
|---|---|---|---|
| Corner load | Load carried at one wheel | Spring force = load / motion ratio | 400 to 1200 lb |
| Motion ratio | Spring travel divided by wheel travel | Wheel rate = spring rate x MR^2 | 0.55 to 1.00 |
| Bump travel | Wheel movement after static ride | Bump spring travel = bump x MR | 1.0 to 4.0 in |
| Loaded length | Free length minus load compression | Ride change compares loaded lengths | Application-specific |
| Bind margin | Length above solid at bump | Bump length minus solid height | Positive with reserve |
| Check | Formula | Target | Why it matters |
|---|---|---|---|
| New rate | Original rate x Na1 / Na2 | Predictable rise | Removing active coils makes the spring stiffer. |
| Cut free length | Original length - pitch x cut coils | Still seats safely | Drop comes mostly from shorter loaded length. |
| Coil index | Mean diameter / wire diameter | About 4 to 12 | Low index raises stress and manufacturing risk. |
| Wahl stress | Kw x 8FD / pi d^3 | Below allowance | Curvature-corrected shear stress increases with load. |
| Solid height | Total coils x wire diameter | Below bump length | Coil bind can damage springs, mounts, and dampers. |
💡Cutting tips and safety
Coil springs is components that are located between the road and the car. Many individual desire to cut a coil spring for two main reasons: cutting a coil spring will lower the car, and cutting a coil spring will stiffen the suspension. The idea is that if you remove material from a coil spring, the coil spring will lower the car and have an increased spring rate.
However, cutting a coil spring will cause many changes to the component at once. When you cut a coil spring, the spring rate, spring length, spring stress, and spring clearance will change. The spring rate of a spring is dependent upon the number of active coils within that spring.
What Happens When You Cut a Coil Spring
By cutting a coil spring, you will remove the number of active coil. As a result, the spring rate will increase due to the fact that the same load will be distributed among a shorter spring. The amount that the spring rate increases will be dependent upon the number of active coils that the spring had initially, and the amount of that active length that is removed.
A spring with many fine coils will experience a greater percentage change in spring rate then a spring with fewer active coils. As a result of the changes to the spring rate, the change in ride height will occur. Additionally, because the spring rate will change the compression of the spring, the change in ride height will occur as a result of the change to the spring rate and the corner weight of the car.
Furthermore, because the motion ratio between the spring and the wheel is not 1:1, the ride height will change due to this unequally movement of the components. You can use a calculator to determine these changes to the spring, as it can process the load of the car, the spring motion ratio, and the bump travel of the spring. If the length of a coil spring is shortened to such a degree that the active length of the spring is less than the solid height of the spring, the spring will reach coil bind.
Every spring has a solid height, which is the height of the spring when the coils of the spring are touching each other. If the bump length of the spring is less than the solid height of the spring, the spring will reach coil bind prior to the wheel reaching the stop of its travel. Because spring bind is undesirable, a margin for bind must be provided for the spring.
The bind margin is the distance between the bump length of the spring and the solid height of that spring. The stress placed onto a cut spring will change. By removing the number of active coils of a spring, the remaining springs will experience increased stress in relation to the load that is placed upon the spring.
Other factors to consider are the material of the coil spring, and the service factor of that spring. Even if the spring would appear to be within limits after being cut, the increased stress upon the spring may cause that spring to be beyond it limits. By cutting a coil spring, the free length and the solid height of that spring will change.
It is essential that the spring can still properly seat within the car at full droop, and that the spring is still captured during its full travel. If the spring was barely captured prior to cutting the spring, the spring may become unseated during travel of the car. Additionally, cutting a spring will change the way that the spring sits within its perch.
If the spring changes the way that it sits within the car, it can lead to side loading of that spring or even buckling of the spring. The tables provided within this article will show the ranges within which the spring will change. These ranges are not guarantees as to the change of each spring.
Each coil spring is slightly different from each other in how the coils of the spring are formed and the pitch of those coils. As a result, one spring may change in a different manner than another spring, even if the same amount of length is removed from each spring. For this reason, it is recommended that a little length be removed from the spring, the spring be measured, and then more length be removed once the car has settled.
The goal for which an individual desires to cut the spring will impact the way in which the spring is to be cut. If the goal is to fine-tune the ride height of a street car, then the individual only needs to worry about the ride height and the bind margin of the spring. However, if the goal is for the spring to change the spring rate of a track car, then the stress upon the spring must also be considered and manage.
Heat should never be used to assist in changing a coil spring. Using heat will change the material properties of the spring, which will reduce the life of that spring due to fatigue. Instead, the spring should be cut, the cut end deburred, and the spring measured against the original specifications of the spring.
If the spring does not meet the specifications required by the car, then that spring is not the starting point for resolving the desired issue of the car. Prior to cutting a spring, the numbers should be run to account for each variable of the spring. The spring rate, spring length, coil bind, and spring stress do not have any variable independent of each other.
The spring that is cut will be the result of each of these variables being consider and balanced with each other.
