Which Spring Should I Order? A Guide to Choosing the Right Coilover Springs

 

buying coilover springs

Upgrading your coilover springs is one of the easiest ways to customize your suspension setup for better handling, comfort, or ride height. But when it comes to buying coilover springs, getting the perfect fit and performance means taking accurate measurements and understanding the right specs for your vehicle. This guide will walk you through everything you need to know before ordering new springs.

 

buying coilover springs

 

1. Know Why You’re Upgrading

Before getting out the tape measure, ask yourself: What’s the goal?

  • Want a stiffer setup for the track?

  • Looking for better comfort on daily drives?

  • Removing or adding weight (like a cage or motor swap) and need more support?

  • Trying to fine-tune ride height?

Your answer will guide you toward the correct spring rate and length.

 

buying coilover springs

 

2. Measure the Free Length (Inches)

The free length is the total length of the spring when it’s completely unloaded and off the car.

✅ How to measure:
Place the spring on a flat surface and use a tape measure to measure from one end to the other. Round to the nearest inch if needed. Common lengths include:

  • 6 inches

  • 7 inches

  • 8 inches

🛑 Why it matters:

Coilovers are designed with a specific shock stroke, meaning there’s an ideal spring length that keeps the shock operating within its intended travel range. If you install a spring that’s too long or too short without accounting for this, your suspension may:

  • Top out or bottom out prematurely

  • Lose effective damping

  • Handle poorly or ride harshly

  • Cause premature shock wear

While it’s possible to use a shorter or longer spring to change ride height or stiffness, doing so without shock stroke can take your damper out of its optimal performance zone.

 

buying coilover springs

 

3. Measure the Inner Diameter (Inches)

The inner diameter (ID) determines if your spring will fit over your coilover hardware correctly.

✅ How to measure:
Use calipers or a ruler to measure the inside width of the spring from one edge to the other. Most standard options are:

  • 2.25 inches

  • 2.5 inches

  • 60mm (≈ 2.36 inches, commonly referred to as 60mm)

🛑 Why it matters:
An incorrect ID can cause the spring to not seat properly on the perch or collar—leading to safety and handling issues.

 

 

4. Choose the Correct Spring Rate (K)

Spring rate, measured in kilograms per millimeter (kg/mm or “K”), determines how stiff your spring is. It describes how much weight is needed to compress the spring by 1mm.

💡 Examples:

  • 6K = Softer ride, more comfortable

  • 8K = Balanced street/track

  • 10K or more = Stiffer, better for performance and handling

🛠️ If you’re unsure where to start, look up your coilover’s base spring rate—this is what your shocks were valved to work with. When changing rates, try to stay within ±4K of that number. For example, if your coilovers come with 8K springs, stay between 4K and 12K. Going outside that range can throw off the damping and make the shock ineffective or uncomfortable, since it wasn’t designed to control such different forces.

 

 

Quick Checklist Before You Buy

  • ✅ Free Length (in inches): 6″, 7″, 8″, etc.

  • ✅ Inner Diameter (in inches): 2.25″, 2.5″, or 60mm

  • ✅ Spring Rate (in K): e.g., 6K, 8K, 10K

 

👉 Ready to upgrade? Shop Function and Form replacement coilover springs here:

Purchase Springs: https://www.f2suspension.com/product-category/springs/

 

This concludes the guide to buying coilover springs.

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