What's the deal with progressive springs? As a bike guy I've learned using a non-linear spring turn can you into a lawn dart faster than chopping the throttle when sliding the rear-end while exiting a corner. I was guessing that that same detached or inconsistent feel you get at 8/10 and above on a motorcycle would transfer over into the car world. Yet, some of the suspension turners swear they're the greatest thing since sliced bread. I've never run on them, so I don’t know if they're worth a damn or not. Anyone got a theory and what makes them better?

 

the idea is that you can get away with more travel and more lowering with one spring. the problem with lowering a car on a stardard coil spring is that you must then tighten up the spring at every interval of travel.

with a progressive spring if you're low you can still have a softer mild bump low speed bump but retain good "clearance force" if things get too threatening to your car's body work.

it basically tries to give you the best of both worlds, nice ride with good resistance to extreme chassis movement. or for racing the ability to maintain good bump travel which keeps your tires contacted with the ground yet not compromise the chassis when push comes to shove (literally)

one of the problems is with progressive springing you need progressive damping. last i checked you can't do that, but that's probably a minimal negative side.

the other problem is that you don't get to choose where it gets progressive so to speak. as in the behavior changes, and sometimes it'll change when it's called for but it's that one time it changes when it's uncalled for that makes you never want to use or recommend them to anyone ever.

 

they are not the be all and end all in performance, but they give a nice, balanced effect to handling vs streetability; which is exactly their purpose

On a bike, the effects are far more pronounced because you have a significantly lighter machine, and it's only spread out among 2 wheels vs 4

 

Also most sportbikes use a non-linear linkage in the rear that does the same thing as a progressive spring by increasing the leverage of the spring as it travels into a compressed state. So you don't need/want a progressive spring back there.

 

Killboy

Wow, I haven't seen that name in a few years (and a few forums). It's good to see your still doing the bike thing on the on dragon.

 

But there is high speed/low speed difference in dampers. I would think this would be an suitable equivalent to "progressive" damping in relation to a soft bump vs sharp bump.

 

As far as I know, only DMS and OHLINS make progressive dampners for aftermarket use. Bilstein might. Bilstein does have OE progressive dampers for sure, not sure about aftermarket.

Main advantage is all low speed traction scenarios / comfort. You are not forced in to a high rate spring at minimal shaft speeds. Allows the car to be much more planted and stable. Same is true on a full droop scenario and you hit a small bump. Less chance of unsettling the rest of the car and loosing grip.

Snow, Tarmac, Gravel, ICE, this is true for any condition.

Cheers,
-mark

 

It is not the same..remember high and low speed events can occur anywhere in the travel (you are braking and hit a bump, you are accelerating and hit a bump or you are cornering an hit a bump or combinations of those). This is where the road racing community has an issues with progressive springs because you are at a different rate in each scenario but the damping is the same because it only depends on the velocity not the position of the shaft. That is why Linear is better in our application. Let me explain further...

The sportbike (and dirt bike for that matter) solution using a linkage is the only proper way to do it that way, the damping stays in sync with the spring it is also the technique used on a formula car or anything that uses a pushrod type suspension (though they don't have to be progressive, they can be). The reason they do it is for low and high vehicle speed differences due to downforce. They are at 150+ mph several times heavier that when they are sitting still so they need it they also use a third spring set-ups for these very reasons (which is an additional canister linking the sides).

So to re-cap progressive ratios (notice not progressive dampers or springs) are useful when the car has very different dynamic loads due to high downforce levels. The are used on loose surfaces in rally so the cars easley transfers load to gain traction on a softish surface. They are not used in tarmac (road) racing with sedans (even though Mark from DMS loves to imply they do). The car will have too much initial roll/dive/pitch and feel sluggish and soft all during the critical transition phase (transition from brake to cornering and then cornering to acceleration).

Like I've stated in the past come with me for a walk around the paddock at an ALMS/World Challenge/Rolex/Grand Am Cup race and try to find a single sedan using progressive suspension of any sort (let alone a winning car).

Unless you are making 2-4 times your own vehicle weight in downforce or racing in the dirt/snow/ice or rain you don't want a progressive suspension. If you race on a paved track with a sedan you want linear rates (this has been proven time and time again). Also as stated before you can not properly dampen a car with progressive suspension unless it has a linkage system that makes it progressive.

 

For the tarmac, progressive = comfort; linear = handling. Couldn't have put it any better chrono.

 

Why do you keep inferring that if it is not your setup or idea, it is no good? I am not implying, I am stating outright that the KST type DMS spring works for tarmac setups!

The key is to match the progression rate to the type of track and surface. A gravel spring does not work on tarmac I agree. But at the same time a progressive tarmac spring, does not work on gravel. Some drivers might perfer one to another, but it is not saying one is better than the other.

I think you are going to get a kick out of the results we will post with your beloved linear spring setup on an OHLINS R/T coilover. The key to an internet forum is to post information to help increase everyones knowledge. My opinion is different from yours obviously, but I have never said anything bad to an OHLINS setup. They pioneered many kits and technologies at the highest, and lowest forms of motorsport. I congratulate them for that. In the same terms, they are not the only company to offer a competitive solution that works and is fast.

Cheers,
-mark

 

Sorry to go a little OT, but I seem to remember that you can actually engineer in the 'progressiveness' of the spring. For example the max:min rate ratio and so on.

If this can be done, then clearly we can achieve a sort of compromise for a fast road/occasional track bearing in mind that we drive on other surfaces as well as dry tarmac.

Finally, what are your (everybody here) thoughts on helper springs. Surely this would be the worst possibly setup as you have one rate then when the helper is at its solid length you instantly get another rate.

[p.s. for a number of engineering applications, springs are made variable rate/progressive to avoid resonance. doubt it's the case here....]

 

A helper spring is not the worst design by any means - it is what it is, a compromise. A helper spring is there to absorb the small bumps in the road that cause minimal compression/rebound events at relatively low speeds without having to go to a progressive spring. For a street driven car, or even a tarmac prepped one, mated to the right damper, it can be excellent.

The thing that makes no sense is how everyone professes to be an expert. The bottom line is there are plusses and minusses to EACH of these designs - progressive/linear/helper, etc. The key to making any car "handle" - is literally trial and error to a large extent. It is running laps over and over with a variety of settings until you arrive at the settings the tires and driver like on that day.

It is impossible to have a car excel in all conditions - low speed bump, mid turn bump, high speed sweeper. The trick is taking copious notes and doing sufficient testing such that the car behaves predicatably, in the drivers eyes, lap after lap. At the end of the day, its the perrenial balancing act of tires/alignment/weight/damper valving/spring tension/weigh distribution/downforce and other things. If there was one "magic" setup, everyone would run it.

 

I agree with this statement concerning the setup discussed anywhere on this forum. It is possible to do this with high end setups that have proper high, low, transition compression and rebound adjustments. There is not a single system on the market that will do this for less than 14-15K $USD, ours included, hence no need to start talking about something that does not effect this conversation.

The main advantage of a progressive or helper spring setup comes into play under droop conditions. Yes the rate of progress is controled, and that is the reason that our tarmac springs do not work for gravel and vise versa ... different applications, different goals to be realized!

Cheers,
-mark

 

Okay, first of all, I am by no means an expert on this and I don't think I have tried to appear as one.
However, I am an engineer and from my point of view, I just don't agree with helper springs.

If you have two springs end to end, the stiffness is much reduced obviously.
For helper springs to actually have any benefit, the helper must at some point compress to a solid length (where it can't compress any longer) during the shocks useful stroke. At this point, the rate suddenly goes back to the rate of the harder spring.

I'm just speculating here, but surely the abrupt change in stiffness would not produce the most predictable handling (?)

As pointed out, it _is_ a compromise, but I think progressive springs are a much better solution. Pregressive rate springs if properly designed will be like having a whole bunch of helper springs stacked together, without the added weight. Now, if your application really cant' or don't need to use the more supple rates, then I suppose going with just a linear rate spring is the best way to go. Which is why I'd say that out of the three, helper springs is the worst solution. That is if an equivalent progressive rate is available. The only thing that helper spring setups have going for them is that they are cheap and likely to be very flexible as you don't have to go and make a completely new spring if you want to change things.

Anyway, that's the way I see it. In actual use things are probably different and I am looking forward to hearing some opinions.

 

oh, flag on the play...
teeny tiny nitpick here, but I think helper springs are typically coils with negligible rates, enough to keep the main coil seated but not enough to contribute to the overall spring rate, cut flat so that when it completely compresses its basically a flat disk.

I think we're talking about tender spring shere. I'm also looking forward to more opinions on the effectiveness of progressive rate springs and some solid evidence of their effect on "predictability" in handling.