How does spring preload affect how a car handles?

[scottzg]

More or less as the question states. My legacy springs had a buttload (metric) of springload, where the rs stuff i was able to compress on to the strut without a compressor. Since 3 wheelin isn't that uncommon, it must have some sort of effect, anyone know exactly what it does? Is it even worth worrying about?

[vrg3]

Well, just from what I know about spring dynamics from Physics 112 taken back in fall of 1998... Preloading a spring effectively increases the spring rate. So a softer spring with more preload can behave like a stiffer spring.

But even if the spring perches don't apply much preload, the weight of the car should apply a lot of it, right?

[scottzg]

yeah, i dont think the preload does anything when the car is sitting on its wheels, the weight of the car compresses the spring more than the preload does.

But the preload would affect how the car behaves when the wheel is at full droop... but how?

[Kelly]

Wouldnt the affect of preload depend on what type of spring your using? As in a progressive vs. liniar type spring.

[jamal]

yes, it would. A linear 132lb/in spring takes 132lbs to compress each inch, whether it's the 1st or the 4th.

The nice thing about preloading springs on coilovers is that you can change the ride height without shorter springs. Without progressive springs, you're not changing the rate, though.

Oh, and I suppose a preloaded spring will rebound more forcefully than one that isn't.

[professor]

this stuff gets confusing but here's a good article

http://www.setrialsriders.org/Tech_Arti ... e%2015.htm

[rallysam]

I can't think of any affect it would have on the handling of the car, whether all feet are firmly on the ground or even when you're three wheelin'.

[Legacy777]

I think where it might come in handy is if you're running over a lot of uneven terrain and getting a lot of wheel travel.

[professor]

it also keeps the spring from getting knocked out of the perch, which I've seen happen several times on cars with aftermarket (shorter) springs

[Legacy777]

Yup.....that's one of my beefs with the lowering springs. I wish there was more (some) preload.

[scottzg]

Thanks for the link, professor, it took me about 10 minutes of squishing a foam ball on my desk to get it.

for those of you that don't want to read the whole thing, the preload adds springrate x 1.amount-of-preload-in-inches to the total spring rate, regardless of how compressed the spring is. A softer spring with more preload will act like a stiffer spring with less preload, but will be stiffer at the top of its travel and softer at the bottom.

[BAC5.2]

Geez, you could have simply asked me.

I've been tuning bike suspension for years, and first and foremost, you set preload.

Ideally, for a bike, you adjust sag with preload. I know for a bike you want to sag 1/3rd of the total travel. 9" travel bike, sag to 3" into the travel. Excessive, it sounds, but like josh said, over rough terrain when using lots of wheel travel, it's important to help keep the wheel on the ground on extension. Force the wheel downwards when everything else wants to go upwards. It's the reason I was so fast on my downhill bike, and couldn't jump worth a damn (without changing setup). The wheels simply never left the ground.

Suspension works both ways. Both controlling compression and rebound, and controlling extension beyond static. Far to high preload creates a bouncy ride (very similar to a high-rate spring), to little, and you float (like a low-rate spring). The key is getting the perfect amount of preload, then adjusting all aspects from there.

On a bike, if you don't score preload, you don't score with any subsequent adjustments. Ride a Wal-mart mountain bike with a zero-adjustment shock, and ride a properly tuned, high performance suspension fork, and compare the two. You never know what kind of effect a properly tuned suspension can have if you've never experienced it.

To put it nicely, in a car when you turn and have inadequate preload, the inside wheels can hop due to lack of preload. The onlything controlling wheel movement is compression and rebound adjustment, and it's controlling an unsupported wheel. It doesn't work well. Now, you can mask that with incredibly stiff spring rates that don't allow you to bottom the suspension very easily (thus not allowing you to lift the insides enough to cause the hop), or you can deal with it properly by having preload properly set up and maintain adequate wheel travel, as well as a far less harsh and uncomfortable ride. Preload is an adjustment that is there for a reason, and it's why lots of coilovers (like Teins) have height adjustment independent of preload settings.