Straight (Linear) vs Progressive Rate Springs - Road Use Knowledge

[Noel]

This is perhaps one of the most common items of upgrades enthusiasts pursue to improve their cars - Replacement Springs to lower their rides. IMO, this is one critical component of the car that needs to be done correctly to ensure YOUR handling is truly improved and not a preception of improvement over what you think is "best".

Biggest question if you don't know till now, what is the difference between straight and progressive springs? Let me explain to you what they truly mean. Fact is, not many people know the differences in behavior between straight and progressive springs. This thread will provide you a basic informed understanding.

Basic Differences - Straight (Linear) vs Progressive Rated Springs

Straight Springs have a spring rating that is linear across the entire length of the spring that it can be compressed. These types of springs can be easily recognized because the space between each winding or spring coil is equal to one another. While Progressive Springs have a spring rating that increases or changes as the spring compression changes. How much it changes depends on the spring type. A progressive spring can be recognized by the fact that the space between every winding or spring coil of the spring is different. It will go to small on one end to large on the other.

Key Characteristics - Straight (Linear) Springs

The most significant characteristic of a straight spring is that it is easy to understand and set up for just about anyone with a basic knowledge on how spring rates work. (The more spring rate there is, the harder the spring will be, the harder the spring, the stiffer the ride.) There is really only one variable to take into account and that is the spring rating, and since the spring rating is consistent. You can calculate how the spring will behave under various "conditions".

This is an advantage that should not be underestimated, specifically under racing conditions. On the tarmac, you want to know exactly what the suspension is doing, how it's doing, how much it's doing it and where it's doing it. The only way of doing that is when the spring behaves the same under different conditions around the track to deliver a consistent handling pattern specific to what you want the car to handle. If comfort is not a part of the equation, it is possible to calculate exactly what spring rate you want at a certain tarmac condition to give you the best response, feel and ultimately - Traction.

While time for setup for road and racing use is somewhat not comparable. How you set up your ride does not change either way. The "informed" consumer will often if not always base their homework and buying research based on the manufacturer/tuners research and development, racing experiences and most importantly race proven results. This will also explain why most of them will if not always recommend straight springs, because that is what they know. However, a sales-pitch like ‘proven on the racetrack’ does not always mean the best solution for the open road. After all, a road car and a track car is somewhat different in demand and performance specifications.

Key Characteristics - Progressive Springs

The most important characteristic of a progressive spring is of course it's variable spring rating value. This makes it harder to calculate or predict it's behavior on any tarmac, but it's much more significantly designed for road use. To understand this, we look at what we want to achieve, just like any race car. The ideal situation for the majority would be the straight-line comfort, combined with the razor-sharp turn-in, feel and control of a race car. Suspension wise, this is somewhat impossible because as soon as you focus the bias on comfort, you automatically lose out on the handling aspect.

This is a balance scale that goes either way. However, with a progressive spring we can get pretty close to a 50/50 setup. A progressive spring will have it's lowest spring rating when it's the least compressed and the highest spring rating when it's the most compressed. When we are driving in a straight line, the majority would not want to feel or obtain feedback on too much of the road.

The majority want it to be a comfortable and relaxed ride but as soon as a twisty road is spotted again, the attention changes to the need for a firm, planted feel with lots of driving feedback from the tires. In a corner, the increased load causes the car to ‘squat’, meaning the suspension gets compressed both front and rear. Because of this compression, the initial comfortable springs stiffen up and start giving you the planted feel and feedback. And the faster you drive, the more feedback and feel will the springs give you, exactly as our race car example but for a road car application.

Choice Factoring - Driving Experiences/Condition Differences

Whatever the spring type that is used, it has to be correctly setup for your car. Factors affecting how you want the car to handle point on what the car is to be used for, whether a road car, weekend sprited/track car or purpose tuned race car. If not, your suspension will not perform at it's optimal peak. A badly setup straight spring is just as bad as a badly setup progressive spring (vice-versa).

It is good to keep in mind that progressive springs don't have infinite adjustability. There is a range in which they will operate optimally, and outside that range performance will drop. You can’t just keep adding load and expect the springs to magically keep up forever. The optimal range however, is much larger than a straight spring will ever have, as the examples have shown.

Does this all mean progressive springs are better than straight springs and the various suspension tuners are talking crap? Not one bit. It ultimately comes down to vehicle application for whatever conditions but for a primarily road use car, a progressive spring will no doubt be a clear vantage over a straight spring setup. A good example is - Racing specified tires. They don’t work very well on the road, because you often cannot get or keep them within their optimum "working" temperature range, much like a race suspension setup will not optimally work on the road if it's been primarily setup for the tracks. If your application is the open road and you want to enjoy it to the best of your ability, you have to chose the right type. And for that application the right type would no doubt be - Progressive Rated Springs.

[Joker]

Outstanding post Noel! Thank you

[goowakjai]

Great write-up Noel! Just what I needed as I'm looking into coilovers and need to find out what would best serve my car for it's intended use.

[Andynolife]

awesome info. ~
just wondering is Eibach Prokit Progressive Rate Springs or not ?

[LannyMCS]

Originally Posted by Andynolife

awesome info. ~
just wondering is Eibach Prokit Progressive Rate Springs or not ?

Eibach ProKit is progressive.

One thing that bothers me about the majority (if not all) progressive springs is that the manufacturers never disclose any type of spring rate info, making it hard to make informed decisions.

Noel, how do think the typical factory strut deals with a progressive spring? In all vehicles that I've been in with progressive springs, it was fairly obvious that the strut's damping abilities did not match up all that well.

[Noel]

Originally Posted by LannyM

how do think the typical factory strut deals with a progressive spring? In all vehicles that I've been in with progressive springs, it was fairly obvious that the strut's damping abilities did not match up all that well.

Yes, Lanny is right about Eibach springs being progressive type springs. And yes, manufacturers do not release specifications on spring rates because of comparison disclaimers. Don't ask me why, but it's just not something they're willing to disclosed even asked.

Honestly, they don't deal too well and I wouldn't use that setup of - Progressive springs with OEM shocks even for road use. It's simply putting premature wear whilst OEM shock rates are not designed for running aftermarket progressive springs. But of course, not everyone has to agree or follow suit.

[SAZABI]

Nice post! I will read it when I go to work tom

[jprovostla]

I totally agree... progressive rate springs {and matching shocks & anti-roll bars] give you a great ride...
I had them on one of my Integras and it transformed the car...
In ordinary driving conditions, it was very comfortable but more controlled than stock...
But when pushing the car on twisty roads and/or with 4 people in the car, you could really feel the suspension hunker down and give a masterful predictable ride...
progressive rate springs are the best of both worlds...

Jacques...

[Ransak]

Originally Posted by Noel

Honestly, they don't deal too well and I wouldn't use that setup of - Progressive springs with OEM shocks even for road use. It's simply putting premature wear whilst OEM shock rates are not designed for running aftermarket progressive springs. But of course, not everyone has to agree or follow suit.

Ok - so, probably a stupid question ... but ... if I was considering installing springs with my stock struts - then I suppose you would suggest I find "Straight springs" rather than progressive?

And, if that is the case, how might you pedict that my every-day road ride will feel (I'm considering H&R lowering springs, which I'm told result in a roughly 2" drop all around)?

[Noel]

Problem is, there aren't any replacement OE straight springs that I'm aware of. If not all, the majority of manufacturers use a progressive spring even OE.

[Ransak]

Ahh ... ok. Makes sense. Tx.

[nachob]

Originally Posted by Noel

This is perhaps one of the most common items of upgrades enthusiasts pursue to improve their cars - Replacement Springs to lower their rides. IMO, this is one critical component of the car that needs to be done correctly to ensure YOUR handling is truly improved and not a preception of improvement over what you think is "best".

Biggest question if you don't know till now, what is the difference between straight and progressive springs? Let me explain to you what they truly mean. Fact is, not many people know the differences in behavior between straight and progressive springs. This thread will provide you a basic informed understanding.

Basic Differences - Straight (Linear) vs Progressive Rated Springs

Straight Springs have a spring rating that is linear across the entire length of the spring that it can be compressed. These types of springs can be easily recognized because the space between each winding or spring coil is equal to one another. While Progressive Springs have a spring rating that increases or changes as the spring compression changes. How much it changes depends on the spring type. A progressive spring can be recognized by the fact that the space between every winding or spring coil of the spring is different. It will go to small on one end to large on the other.

Key Characteristics - Straight (Linear) Springs

The most significant characteristic of a straight spring is that it is easy to understand and set up for just about anyone with a basic knowledge on how spring rates work. (The more spring rate there is, the harder the spring will be, the harder the spring, the stiffer the ride.) There is really only one variable to take into account and that is the spring rating, and since the spring rating is consistent. You can calculate how the spring will behave under various "conditions".

This is an advantage that should not be underestimated, specifically under racing conditions. On the tarmac, you want to know exactly what the suspension is doing, how it's doing, how much it's doing it and where it's doing it. The only way of doing that is when the spring behaves the same under different conditions around the track to deliver a consistent handling pattern specific to what you want the car to handle. If comfort is not a part of the equation, it is possible to calculate exactly what spring rate you want at a certain tarmac condition to give you the best response, feel and ultimately - Traction.

While time for setup for road and racing use is somewhat not comparable. How you set up your ride does not change either way. The "informed" consumer will often if not always base their homework and buying research based on the manufacturer/tuners research and development, racing experiences and most importantly race proven results. This will also explain why most of them will if not always recommend straight springs, because that is what they know. However, a sales-pitch like ‘proven on the racetrack’ does not always mean the best solution for the open road. After all, a road car and a track car is somewhat different in demand and performance specifications.

Key Characteristics - Progressive Springs

The most important characteristic of a progressive spring is of course it's variable spring rating value. This makes it harder to calculate or predict it's behavior on any tarmac, but it's much more significantly designed for road use. To understand this, we look at what we want to achieve, just like any race car. The ideal situation for the majority would be the straight-line comfort, combined with the razor-sharp turn-in, feel and control of a race car. Suspension wise, this is somewhat impossible because as soon as you focus the bias on comfort, you automatically lose out on the handling aspect.

This is a balance scale that goes either way. However, with a progressive spring we can get pretty close to a 50/50 setup. A progressive spring will have it's lowest spring rating when it's the least compressed and the highest spring rating when it's the most compressed. When we are driving in a straight line, the majority would not want to feel or obtain feedback on too much of the road.

The majority want it to be a comfortable and relaxed ride but as soon as a twisty road is spotted again, the attention changes to the need for a firm, planted feel with lots of driving feedback from the tires. In a corner, the increased load causes the car to ‘squat’, meaning the suspension gets compressed both front and rear. Because of this compression, the initial comfortable springs stiffen up and start giving you the planted feel and feedback. And the faster you drive, the more feedback and feel will the springs give you, exactly as our race car example but for a road car application.

Choice Factoring - Driving Experiences/Condition Differences

Whatever the spring type that is used, it has to be correctly setup for your car. Factors affecting how you want the car to handle point on what the car is to be used for, whether a road car, weekend sprited/track car or purpose tuned race car. If not, your suspension will not perform at it's optimal peak. A badly setup straight spring is just as bad as a badly setup progressive spring (vice-versa).

It is good to keep in mind that progressive springs don't have infinite adjustability. There is a range in which they will operate optimally, and outside that range performance will drop. You can’t just keep adding load and expect the springs to magically keep up forever. The optimal range however, is much larger than a straight spring will ever have, as the examples have shown.

Does this all mean progressive springs are better than straight springs and the various suspension tuners are talking crap? Not one bit. It ultimately comes down to vehicle application for whatever conditions but for a primarily road use car, a progressive spring will no doubt be a clear vantage over a straight spring setup. A good example is - Racing specified tires. They don’t work very well on the road, because you often cannot get or keep them within their optimum "working" temperature range, much like a race suspension setup will not optimally work on the road if it's been primarily setup for the tracks. If your application is the open road and you want to enjoy it to the best of your ability, you have to chose the right type. And for that application the right type would no doubt be - Progressive Rated Springs.

Noel, nice writeup but I wanted to know if the TSX stock springs are linear or progressive. Most stock sprints are usually progressive. Do you know? I happen to think the suspension on my TSX is awesome stock and I have modified quite a few cars in my day. This has the best stock suspension I have ever driven in terms of balance between performance and comfort.
Thanks,

[LannyMCS]

Originally Posted by nachob

Noel, nice writeup but I wanted to know if the TSX stock springs are linear or progressive. Most stock sprints are usually progressive. Do you know? I happen to think the suspension on my TSX is awesome stock and I have modified quite a few cars in my day. This has the best stock suspension I have ever driven in terms of balance between performance and comfort.
Thanks,

The front springs consist of 6 equally spaced coils, all the same diameter, not counting the lower mounting coil. So they are linear rate.

The rear springs consist of 7 coils, evenly spaced and equal in diameter up until the bottom two coils, which have the same spacing but are slightly smaller in diameter, which make them a little bit progressive; hardly enough to mention though. Very similar to the design of the Comptech 110-155.

[Noel]

In short, what Lanny is saying ...

Front Springs - Straight
Rear Springs - Progressive

[nachob]

Thank you Gentlemen, much appreciated.

Ignacio