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Spring Rates Explained

Posted by Dežru Suspension Engineering on Nov 23rd 2025

Understanding Spring Rates: What They Actually Do — and How to Choose the Right Ones

What Is a Spring Rate?

A spring rate is simply the amount of force required to compress a spring by one inch (or one millimeter, depending on the standard).

Examples:

  • 350 lb/in → takes 350 pounds of force to compress the spring 1 inch

  • 450 lb/in → stiffer

  • 550 lb/in → even stiffer

But the real-world behavior of a spring has far more to do with vehicle weight, motion ratio, ride height, and valving than the raw number printed on the coil.

This article breaks down what spring rates truly do — and how Dežru selects proper rates for our Spec-S, Spec-R, and Spec-RS coilovers.

Spring Rate = How Much the Spring Resists Compression

A higher spring rate means:

  • Less body roll

  • Less squat under acceleration

  • Less dive under braking

  • More direct road feel

  • Less comfort

A lower spring rate means:

  • Softer ride

  • More suspension movement

  • More body roll

  • Better comfort

  • More weight transfer during performance driving

But this is only the beginning.

Wheel Rate vs Spring Rate (Not the Same Thing)

The number on the spring is not what the tire feels.

Suspension arms have motion ratios — the wheel doesn’t move 1:1 with the spring.
For example:

If your spring compresses 1 inch but the wheel only moves 0.8 inches, your actual “wheel rate” is:

Wheel Rate = Spring Rate × (Motion Ratio)²

So with a 450 lb/in spring:

450 × 0.8² = 288 lb/in wheel rate

That’s why two vehicles using “450 lb/in springs” can feel wildly different.

Every Dežru kit uses spring rates based on:

  • Actual chassis motion ratio

  • Target comfort level

  • Target performance profile

  • Shock valving development

  • Intended use (daily, track, tarmac rally)

How Spring Rate Works in a Fixed-Length Coilover (Dežru Design)

This is critical and unique to your products:

Dežru coilovers DO NOT use adjustable hub brackets.

Ride height is adjusted only via the spring perch + helper spring, not by changing shock length.

This means:

✔ Spring rate selection is far more controlled and predictable
✔ Shock stroke is always in the correct operating range
✔ Valving is matched exactly to the designed spring rates
✔ No travel is lost from “slamming” the body into the lower mount

Your linear spring + helper spring architecture means:

  • Preload does not increase stiffness

  • Preload does not meaningfully change ride height

  • Helper springs collapse at static height and do not increase spring rate

  • Spring rate stays constant throughout compression

This keeps the suspension behaving exactly as engineered.

Understanding Spring Rate vs Preload vs Ride Height

A very common misconception:

Increasing preload does NOT increase spring rate.

Spring rate is a physical property of the spring itself.

Preload:

  • Changes initial spring position

  • Reduces droop

  • Can make the ride feel harsher

  • Does not stiffen the spring

Ride height:

  • On Dežru kits, is adjusted only via perch position, not preload.

Spring rate:

  • Is constant, regardless of height.

How We Choose Spring Rates at Dežru

Every Dežru platform goes through:

1. Motion Ratio Analysis

We model control arm geometry so the wheel rate is correct for the chassis.

2. Vehicle Weight & Distribution

GR Corolla vs WRX vs BMW vs Porsche — all have different weight transfer needs.

3. Intended Use

We design for three core categories:

Touring / OEM+

  • Subtle improvement

  • Smoother ride

  • Minimum added NVH

  • Ideal for daily drivers

Typical: 350/350 lb/in

Sport / Aggressive Street

  • Sharper response

  • More neutral balance

  • Less body roll

Typical: 450/450 lb/in

Race / Track / Rally

  • Higher wheel rate

  • More platform stability

  • Less pitch/roll

  • Works with sticky tires

Typical: 550/550 lb/in (or custom)

For rally or tarmac motorsport, we often run decoupled front/rear rates depending on platform.

Why Not Just Run the Stiffest Springs Possible?

Because springs don’t work alone — they work with shock valving.

A spring that is too stiff for the valving:

  • Feels harsh

  • Skips over bumps

  • Reduces traction

  • Increases stopping distance

  • Makes the car unpredictable

Every Dežru shock is valved specifically for the rate ranges we supply.

This ensures:
✔ correct low-speed support
✔ correct high-speed compliance
✔ correct rebound control
✔ correct compression behavior

Overspring + undervalve is a common problem in cheap coilovers — and exactly what we avoid.

Helper Springs Do Not Change Spring Rate

A helper spring:

  • Keeps the main spring seated

  • Maintains contact at full droop

  • Collapses fully at ride height

  • Does not affect stiffness

  • Does not change handling

  • Does not alter the effective rate

This is critical for your customers to understand:

A Dežru helper spring is NOT a progressive spring.
It is a positioning spring.

The main spring does 100% of the actual load-bearing work.

What Happens If Spring Rates Are Too Soft?

  • Excessive body roll

  • Slow steering response

  • Brake dive

  • Squat under acceleration

  • Bottoming out

  • Loss of mid-corner stability

What Happens If Rates Are Too Stiff?

  • Harshness over road imperfections

  • Loss of mechanical grip

  • Tire skipping

  • Poor bump absorption

  • Increased NVH

  • Fatigue and chassis wear over long term

Balance is everything — and that balance is why Dežru pre-selects rate options suited for each platform.

Summary: Spring Rates in the Real World

✔ Spring rate = force needed to compress the spring

✔ Wheel rate ≠ spring rate

✔ Fixed-length shock design means rates stay consistent

✔ Helper springs do NOT increase stiffness

✔ Preload does NOT change spring rate

✔ Proper rates are matched to:

  • chassis

  • motion ratio

  • vehicle weight

  • intended use

  • shock valving

Choosing a spring rate isn’t about “stiff vs soft.”
It’s about engineering a balanced, predictable suspension system — and that’s the backbone of every Dežru coilover kit.

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