Setting Coilover Preload Correctly
Preload is one of the settings most coilover owners either ignore or get wrong. It is also one of the settings that has the most impact on how the car feels at the very beginning of suspension travel. Get it right and the car handles predictably. Get it wrong and you can end up with a rattling helper spring, inconsistent ride height, or a car that behaves strangely over small bumps.
Understanding Coilovers and Preload
What Are Coilovers?
A coilover combines a coil spring and shock absorber into one integrated unit, which reduces unsprung weight compared to separate components. The threaded shock body lets you adjust ride height by moving the spring perch up or down. A quality coilover kit is the foundation of any serious performance suspension upgrade. It gives you control over ride height, damping, and spring preload as independent adjustments. Here is the key point. On a well-designed coilover kit, preload and ride height are separate settings. You should be able to change one without automatically changing the other.
On some entry-level kits, preload is tied directly to ride height. Threading the perch down to lower the car simultaneously changes the preload. On higher-quality kits, a separate adjuster lets you set your stance and then dial in preload independently. Knowing which type of kit you have is the first step.
What Is Coilover Preload?
Preload is the amount of compression applied to the coil spring before any of the car's weight is on it. It is measured by how much the spring is compressed from its free (unloaded) length when the coilover is assembled at your chosen ride height.
Zero preload means the spring is sitting loosely in the perch with no compression applied before the car's weight loads it. Some preload means the spring is already slightly compressed at ride height before the car sits on it.
The Importance of Preload in Suspension
Keeps the spring fully seated. A spring without adequate preload can momentarily lift off the perch during suspension extension. On kits with a helper spring, zero preload is the most common cause of the metallic rattle people hear over small bumps.
Controls initial suspension response. A small amount of preload stiffens the very beginning of spring travel, making the car respond more crisply to small inputs. Too much makes the first part of travel overly firm.
Affects transition through travel. A spring with more preload is stiffer in the early portion of travel. Less preload is more compliant at the start, progressively firming as it compresses further.
Preload vs. Ride Height: The Confusion Most Owners Have
The Key Distinction
Lowering the car by threading the perch down does not necessarily change preload. Changing preload does not necessarily change ride height. On a quality coilover kit with separate adjustment mechanisms, these are two different operations. The confusion arises when owners try to get the car as low as possible and end up with zero or negative preload. The helper spring floats. The rattle starts.
This is the part that trips up most coilover owners. Lowering the car by threading the perch down does not necessarily change preload. Changing preload does not necessarily change ride height. On a quality coilover kit with separate adjustment mechanisms, these are two different operations that happen to share the same hardware.
Factors Influencing Preload Settings
Spring rate. A stiffer spring needs less preload to achieve the same initial response. A softer spring may need more.
Ride height. Very low setups need careful attention to ensure the helper spring stays engaged. The lower the car, the more critical correct preload becomes.
Intended use. Street use: 2 to 5mm of preload is usually ideal. Track use: 4 to 5mm for more consistent behavior at speed.
How to Properly Adjust Coilover Preload
Tools Required
Coilover spanner wrench (included with most kits). Measuring tape or digital calipers.
Step-by-Step Adjustment Process
Step 1. Measure the free length of your spring. Remove it from the coilover and measure its uncompressed length. This is your reference.
Step 2. Set your desired ride height first. Ride height is set by the position of the spring perch. Get the car to the height you want before adjusting preload.
Step 3. Measure the installed spring length at your chosen ride height. Measure from coil to coil.
Step 4. Calculate your preload. Preload equals free length minus installed length. If your spring has a free length of 200mm and the installed length is 197mm, you have 3mm of preload. For most street setups, 2 to 5mm is a good starting point.
Step 5. Adjust the spring perch or preload collar to hit your target. Torque the locking collar. Recheck ride height after any preload change.
Testing and Fine-Tuning Your Setup
After setting preload, go for a drive over varied roads including small bumps and smooth sections. Listen for rattles from the spring area, which indicate insufficient preload. If you hear rattling over small road imperfections, add a millimeter or two of preload and recheck.
Feel how the car responds to small inputs. If the initial response feels overly firm or the car feels stiff over very small bumps, reduce preload slightly. If the car feels vague or loose over small inputs, add a small amount of preload.
Adjusting Based on Feedback
Street Use
Start with 2 to 3mm. Adjust up for rattles or vague initial response. Adjust down if the car feels stiff over small road texture.
Track Use
Start with 4 to 5mm on kits like BC Racing, KW, or Fortune Auto. More preload gives more consistent behavior. The suspension sees full travel frequently at speed. Reduce if the car feels harsh over curbs.
Seasonal Changes
Lower spring perch positions reduce unsprung weight loading and sometimes mean insufficient preload once the car is raised back up for winter. Recheck preload after any height change.
Frequently Asked Questions
What is coilover preload and why is it important?
Preload is the initial compression applied to the coil spring before the car's weight loads it. Correct preload keeps the spring seated properly at all times, prevents helper spring rattle, and controls the initial response of the suspension. Getting it right means the car handles predictably across the full range of road conditions.
How do I adjust the preload on my coilovers?
Measure the free length of your spring. Set your ride height first. Measure the installed spring length at that ride height. The difference is your current preload. Adjust the spring perch or preload collar to reach your target, typically 2 to 5mm for street use.
What factors affect the correct preload setting?
Spring rate, ride height, and how you use the car. Stiffer springs need less preload for the same initial response. Lower ride heights may require careful attention to avoid zero preload. Track use benefits from slightly more preload than a pure street setup.
Can I set coilover preload without professional help?
Yes. It requires a spanner wrench, measuring tape or calipers, and the ability to measure spring lengths accurately. The math is simple. Free length minus installed length equals preload. If you are comfortable doing basic suspension measurements, this is a job you can do yourself.
What are common mistakes to avoid when setting coilover preload?
Running zero or negative preload, which causes the helper spring to float and rattle. Confusing ride height adjustment with preload adjustment and changing both when you only intended to change one. Not rechecking preload after any ride height change.
How do driving conditions influence coilover preload adjustments?
Rough roads and track use with aggressive curb strikes benefit from slightly higher preload for more consistent behavior. Smooth daily driving on well-maintained roads can run lower preload for a softer initial response. Change preload seasonally if you change ride height for winter.
Preload Settings Across Major Brands
KW Suspension, BC Racing, Fortune Auto, and Feal all treat preload differently in their design philosophy. KW Suspension specifies zero preload as the baseline for their V1 and V2 Series on most street applications. Their linear spring rate maintains contact through the full suspension travel range. BC Racing BR Series instructions call for 5mm of preload on daily driven cars. This prevents spring float at full droop. Fortune Auto recommends consulting their tech line for platform-specific preload settings, since their stiffer spring rates change the calculation significantly. Feal Suspension, with their high-spring-rate track kits, often runs deliberately higher preload to prevent spring unseating under aggressive droop conditions.
The wrong preload setting on any coilover kit produces noise, inconsistent damping behaviour, and premature spring wear. It is one of the most commonly skipped steps in a DIY install and one of the most common sources of post-install complaints. Get it right the first time. If you are unsure about the correct setting for your specific coilover kit and spring rate combination, call us at 1-800-460-9106. We have the brand-specific data for every kit we carry and can walk you through the setting in under five minutes.
Correct preload is a five-minute step that protects a multi-year investment. Every coilover kit you install deserves it. Every one that skips it will eventually remind you why it matters.
Not Sure Which Kit Is Right Before You Start Setting Preload?
Getting preload right starts with having the right kit for your car and your use case. BC Racing, KW, Fortune Auto, Ohlins, Feal, Tein. We know which ones work best on your platform and we will tell you straight which direction to go.
Call us. That conversation has saved a lot of people from buying the wrong kit and starting a setup from the wrong place.
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