What is the average life span of springs?

[Loren]

Interesting to read some of the misconceptions about springs. Rust-induced problems aside, a suspension coil spring should last 20 years or more. (as stated above, "the lifetime of the car") Rust changes things greatly, of course, and can reduce the spring rate and lead to breakage.

What happens when a spring "sags" over time? It doesn't become softer. The rate of the spring remains constant as it is a factor of the thickness of the spring wire, the diameter of the spring and the number of coils. All that changes when a springs sags is the free length of the spring... until/unless it sags enough that the coils of the spring touch (coil bind). In the case of coil bind, the spring doesn't become softer, it becomes STIFFER. Fewer coils in the spring rate calculation yield a stiffer rate.

What happens more than anything else is that shocks (and/or struts) wear out. Almost all modern shocks have a nitrogen charge in them to help prevent the oil inside them from foaming under hard conditions (bumpy roads that move the shock shaft rapidly up and down and create heat). A side-effect of this nitrogen charge is that it adds to the spring rate of the suspension, and the suspension designers account for this in their design. Usually, the first thing to go in a shock as it ages is the nitrogen charge... which removes that added spring rate and makes the whole suspension feel softer. Often, it will even cause the car to lose some ride height... up to an inch or so.

So, if you think you have "bad springs" because your suspension feels soft, think again. Take a look at your springs. Unless they're eaten away with rust, they're NOT any softer than they ever were. If they're eaten away with rust, obviously they need to be replaced. If they're not rusty... put new shocks/struts on the car and be happy.

Factory shocks on most cars usually start losing some of their performance by 20-30k miles and are pretty weak by 40-60k miles. "Completely shot" is a matter of what you expect from them, but with the exception of OEM Bilstein shocks, pretty much any shock is going to be completely dead by 60-80k miles.

Oh, and fitting stiffer aftermarket springs with stock shocks will cause those shocks to wear out about twice as fast. Fitting springs that are too short and/or cutting bump stops will often allow the shock (either aftermarket OR stock) to go beyond its designed range of motion and bottom out doing instant damage to the internal shock valving.