One thing I have come across several times in the "Post your suspension mods" thread is the use of "Progressive Springs." I would just like some clarification as to what the progressive springs are atempting to accomplish.

In the suspension that I have designed, I have incorporated the progression/linearity of the wheel rate into suspension components and left the springs linear (engineering progressive/regressive springs aren't easy).

Basically, do the progressive springs you guys put in your cars bring the wheel rate to a linear rate, increase a fairly linear rate to a progressive rate, or change a regressive rate to a progressive rate?

Also, what are the typical applications for progressive springs (such as drag racing or autocross)?

 

Ok, If I understand correctly here are your answers:
Most people do progressive to go lower and keep a somewhat soft ride. It also keeps the suspension from bottoming out. So you get a smooth ride around town and can hit the autox or whatnot and have a good stiff suspension in the corners. Every progressive spring company has their own little formula of how stiff the spring gets with every inch of compression. I'd say typically that most people use them for autox for the reason I stated above.

 

OK, so the idea is the you can lower your ride, have a decent normal wheel rate for whatever you want to do with it (autox or whatnot) but you have some progression so your car doesn't bottom out if it hits a big bump. Makes sense.

I don't understand how you can get a smooth ride around town but suddenly have a stiff suspension when you want to autox. Do you make some kind of adjustments to get these settings?

 

I'm pretty sure You can't get a smooth ride one minute and then have a stiff suspension for competition the next with the same set of Springs, There is no adjustment on Progression springs.
I guess You can use them to Autox, But IMO you'll have too much travel and not enough response around corners.

Maybe someone should produce something like that.
A Progressive Spring that can be turned down/disengaged and then a Stiffer Spring could sit inside the Progressive Spring and engaged at a full turn of a bottom perch.?!

Hmmm, Sounded easier in my head then typed.

 

Well, you could use a helper spring. Our Baja uses something similar so that it can absorb big bumps but still have the ride rate that we want. It's basically a softer spring that runs with the harder spring on the same shaft. You need an adapter between the two springs in order for them to stay aligned. What happens when the springs compress is that the softer spring compresses the fastest. Once that spring bottoms out, the hard spring is the only one acting on the system and you're at a harder rate. This gives an extremely progressive rate for landing jumps.

The problem with this is that adding preload still wouldn't change your rate. You'd just end up with a higher ride height and a suspension that has less available rebound.

I actually like your idea about the secondary spring inside the main spring. You could have a shorter spring inside the main spring that would normally just be loose or just not against the main perches. Then, when you want to use the additional spring (for a stiffer suspension) you just crank the perches on the inside spring or somehow lock it into place. That way you could have the soft suspension around town and easier adjust your spring rate for racing.

Again, might be harder than it sounds, but the gears are turning.

 

Its not a night and day difference, but one you can feel. I say smooth, because the stock springs on my MINI were stiff as hell. When I got my progressive rated springs, it wasn't so rough over bumps in the roads and such. The stiffness grows a "x" rate for every inch of compression. So the first inch is 160, the next inch is 280 and the third inch is 360, etc depending on how much travel you have. Those are numbers I made up to give you an idea of what I'm talking about. They are made a certain way to give the spring that property, check out H-Sport Springs for an example of what I'm talking about. The fronts' rates vary from 173-195 lb/in and the rears are 160-300 lb/in.

 

I understand what a progressive rate is, I was just uncertain what kind of suspension people with progressive springs were trying to achieve. Having progressive springs doesn't mean that your wheel rate is going to be progressive. If your suspension geometry yields a regressive rate, equally progressive springs would change your wheel rate to a linear rate, which is usually ideal for racing.

BTW, when a spring compresses, each inch stacks on the previous inch. For example, with your progressive springs that vary from 160 to 300 lb/in, the first inch would be 160 lbs, then the next inch would 160 plus the rate for the next inch. So, in order to compress the spring 2 inches it would take, for example, 360 lbs, then 600 lbs at the next inch. The compression you described would be a regressive spring rate.

 

Doh! You are correct sir. I remember an article that described it as in your first paragraph. I think it was an Import Tuner article. Thanks for the clarifications, I enjoy learnng new things and suspension is one of those things I know just a few basics but nothing major. I could probably tune my own street/occasional track suspension (soon to consist of adjustable coilovers and that's it) to my liking, not necessarily the "best" but the best for me.

 

Since I want consistancy of handling, I would not use a spring that varies
as it compresses.

No one on this site has the ability to tell you the variety of street-driven corners/pavements/etc. that you would drive through/on in a year and the amount of variable spring rates needed for each of them.
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For a given race track, I now have consistancy and measureable corners,
and can now calculate what is needed. Generally setting the suspension
to give me the greatest speed exiting the corner leading to the longest straightaway..............and then varying to give me the greatest speed exiting the corner leading to the second longest straightaway....and so on.

Unless a person is good at math and/or gets paid a lot, it's not worth it
for me to use springs that vary in rate as they change height.

and when I return to that track next time, I can set up the car quicker.
But those springs that I engineered for that particular track will probably only work well on that particular track.-Bob