What is the spring rate of an RC car?
The spring rate is the stiffness of the suspension springs, defined as the amount of force needed to compress the spring by a given distance. In RC cars, it’s usually expressed in newtons per millimeter (N/mm) or pounds per inch (lb/in). Higher values mean stiffer springs; lower values mean softer springs, and both interact with dampers, weight, and track conditions to determine how the car behaves.
What spring rate means for performance
In practical terms, the spring rate determines how much the chassis can dip, twist, and recover when hitting bumps or during cornering. A stiffer spring rate reduces body roll and helps control harsh landings, but can hurt grip on rough surfaces. A softer rate increases traction and comfort on small irregularities but may make the car feel wobbly or floaty on smooth pavement.
To gauge the effect, consider the balance between front and rear springs, the track or surface, and how the dampers are tuned. The same spring rate can perform differently on different surfaces, so drivers often adjust multiple components to achieve the intended handling characteristics.
How spring rate is expressed and measured
Spring rate is commonly listed in N/mm or lb/in, and the two units are roughly equivalent in spirit (1 N/mm ≈ 5.7 lb/in). To measure it directly, you apply a known force to the spring and record how much it compresses; the ratio F/x gives the rate. In RC cars, manufacturers’ specifications and real-world testing with different springs are the typical routes to tuning rather than doing a laboratory measurement on every shock.
Note that the spring rate you see published for a given spring is for the spring alone; in RC cars, the effective rate also depends on how the spring sits inside the shock, preload, and the damper oil, so final feel comes from the full suspension package.
Below is a concise guide to common starting points and how to think about them.
Common starting points for spring rate by category (soft to firm ranges)
- On-road touring and street cars: front 1.2–2.0 N/mm; rear 1.8–2.8 N/mm
- Off-road buggies and short course trucks: front 1.0–2.5 N/mm; rear 1.5–3.5 N/mm
- Soft/low-traction surfaces or drifting setups: front 0.8–1.5 N/mm; rear 0.8–1.5 N/mm
In practice, use these ranges as starting points. The exact choice depends on weight distribution, damper settings, wheel/tire contact with the ground, and your driving style.
Factors that influence the ideal spring rate
Several variables determine the best spring rate for a given car and track. Understanding these interactions helps you tune more effectively:
- Car type and role: on-road, off-road, or drift cars each benefit from different front/rear balance.
- Weight distribution and center of gravity: heavier front or rear ends may require corresponding adjustments in spring stiffness.
- Track surface and grip: smooth, high-traction tracks may favor firmer springs, while rough or loose surfaces favor softer springs for maintainable traction.
- Damper oil viscosity and compression/rebound settings: springs don’t act alone; dampers convert spring movement into controlled motion, so tuning one often requires adjusting the other.
- Ride height and preload: changing preload or ride height effectively alters the active spring rate during operation.
To dial in a setup, start with a balanced mid-range rate for front and rear, test on your typical surface, and adjust in small increments, re-testing after each change. Keeping track of how each change affects grip, steering response, and compensation for bumps helps you converge on a stable, predictable feel.
Summary
The spring rate of an RC car is a fundamental tuning knob that defines how stiff or soft the suspension feels. It interacts with dampers, weight distribution, and track conditions to shape grip, stability, and responsiveness. Use manufacturer specs as a baseline, then tailor front and rear rates to your car type and typical surfaces, testing in small steps to achieve the desired balance. Remember that the best setup is the one that fits your driving style and the conditions you most often race or drive in.
What does 7K spring rate mean?
That translates to 7.1kg/mm, usually known simply as a “7K spring.” In Newtons-per-millimeter, it's 70N/mm. Going up in spring rate — increasing the spring's stiffness — means moving from 400 lb/in, up to 450 lb/in, for example. For softer springs, it's the other direction.
What does a 12k spring rate mean?
Spring rate measures how much force it takes to compress a spring one unit of distance. In metric coilovers, that's in kilograms per millimeter (kg/mm), often shown as “k”. Example: A 6k spring requires 6kg of force to compress 1mm. A 12k spring is twice as stiff as a 6k.
What's a good spring rate?
How To Choose Spring Rates For Your Car
- 0.5 -- 1.5 Hz for passenger cars
- 1.5 -- 2.0 Hz for sedan racecars and moderate downforce formula cars
- 3.0 -- 5.0+ Hz for high downforce racecars
How to measure RC car springs?
Until the veneer. Caliper. Just hits the end. Taking no pressure. Right there there's no play in there that's perfect okay so that's telling us. The total length that that spring is 20.16.
