Question 1

What is spring constant?

Accepted Answer

Spring constant (k) is the stiffness of a spring: the force needed to extend or compress it by one unit of length. From Hooke's Law: F = k × x. SI unit: N/m (newtons per meter).

Question 2

How do I convert lbf/in to N/m?

Accepted Answer

1 lbf/in = 175.127 N/m. Multiply lbf/in by 175.127 to get N/m, or divide N/m by 175.127 to get lbf/in.

Question 3

What is the difference between N/mm and kN/m?

Accepted Answer

1 N/mm = 1000 N/m = 1 kN/m. The two units are equal in magnitude. N/mm is preferred in mechanical engineering; kN/m in civil and structural engineering.

Question 4

What spring constant do car suspension springs typically have?

Accepted Answer

Passenger car coil springs typically range from 15 to 35 N/mm (15,000–35,000 N/m) for independent suspension. Sports cars and performance vehicles may use stiffer springs of 40–80 N/mm. This is often expressed as 1.5–3.5 kgf/mm in older catalogs.

Question 5

How do springs in series and parallel combine?

Accepted Answer

Springs in parallel add directly: k_total = k₁ + k₂. Springs in series combine as reciprocals: 1/k_total = 1/k₁ + 1/k₂. Two identical springs in parallel double the stiffness; in series they halve it.

Kilonewton per millimeter to Newton per millimeter

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