Why Progressive Rate Springs?

First, to clarify the title, I know what they are and I know what they do. I'm trying to find springs for my Bullitt, and everything I find is progressive rate, even if the spring rate is the same or close to the same as stock. I don't get it. I've never used them, but in theory I would think that handling would be more predictable with linear rate springs. The car rides fine now and I don't feel a need to make it better, I just want to lower it a bit and maintain or improve handling. So why doesn't anyone seem to make a linear rate lowering spring for this car? Is it like this with all cars? I don't know, because in the past I've always gone with coil overs.

Linear rate springs are more predictable and the main reason I won't run a progressive rate spring.

My theory is that the companies know their audience and the typical mustanger just drives in a straight line and wants that smooth ride quality.

Which setup works best seems to depend on the vehicle. In the Jeep, I'm currently running linear springs up front, progressive springs in the rear. In my case, the progressive springs definitely work better in back: less change in ride and handling when there's people or weight in the back, and even though they're significantly stiffer at ride height than my previous linear springs, they don't ride any worse.

Progressive springs are also longer for a given stiffness at ride height, which in my case, was just enough to avoid me having to worry about dropping springs at full suspension droop. And they stiffen up gradually enough (and enough overall) coming up to full compression that even with the not very progressive stock bumpstops, no bump is enough to bottom it out hard and upset the thing.

Up front, where I have bigger, squishier bumpstops and a much more constant amount of weight on the suspension, I don't see a reason to go for progressive springs, and they'd likely be a bit less predictable (with no benefit in return).

Progressive rate springs are super nice as far as NVH is concerned, but as Spoolpigeon said, they are infinitely harder to tune. You have the short coils, the long coils, the total amount of each size coil, suspension travel, damper rebound, etc..

Linear is easier, because the math is simple.

Matching shocks to progressive springs is definitely harder. I still have to get that fully figured out on the Jeep. The rear end is pretty good for the most part, but if you hit a dip that throws the rear to full compression in just the right way, it'll rebound violently to almost full extension, then come back down and settle. Not exactly good.

Can you add some high speed compression and high speed rebound?

Appleseed wrote: Can you add some high speed compression and high speed rebound?

I'm thinking that's the fix. Mostly the high speed rebound. I'm just waiting until my new front shocks show up, as I got longer ones due to moving the mounts. I'm going to move the current fronts to the rear (they're valved a bit heavier than the current rears) and then decide from there on what adjustments I want to make.

Many people like the way the progressives Flo better in daily driving.

I think a lot of aftermarket springs are progressive because linear can be harsh on the street. Stiff all the time. Crack in the pavement? BAM! Pothole? BAM! Driveway? BAM! Most people don't like that.

In reply to Appleseed:

The springs it has are linear rate. 600 lb/in front and 250lb/in rear, and it rides fine on the potholed roads of northern Ohio. This reminds me of another thing I don't get - why don't spring makers list spring rates?

I had a set of springs made for my '64 Oldsmobile by Eaton Detroit spring in the 90s. My recollection is they weren't terribly expensive and they will customize the ride height and rate for you.

Some progressive springs are simply to take up a given space and have a shorter stiffer spring.

The Eibachs in my ZX2SR were like that, particularly in the rear.

In reply to bravenrace:

Because if they told you the rates, you'd see that their springs are probably nowhere close to stiff enough to make up for the height they took out.

I dont know the year of your bullet, new edge or s197? I tried searching and got annoyed because as you say most are progressive. But i found steeda springs to be linear, i believe, so double check me.

Im with everyone else i do not care for progressive springs

http://www.steeda.com/steeda-mustang-competition-springs-555-8241/

I cant remember who it was (maybe Gullstrand or Adams) anyway they said the with progressive springs you sacrifice ride height for the needed spring rate.

When setting up Motorcycle suspension you set the sag. This is the amount of compression from fully extended to ride height with rider seated. Then when braking a very slight brake application causes more dive than you would experience with standard wound springs. Thus you loose ride height, and create dive momentum that has a negative impact on motion control and rider feel and traction in the end.

Most lowering springs are progressive to help keep you from bottoming the strut the higher rate only comes in on the higher travel areas. You'll more then likely never notice the effect.

Appleseed wrote: I think a lot of aftermarket springs are progressive because linear can be harsh on the street. Stiff all the time. Crack in the pavement? BAM! Pothole? BAM! Driveway? BAM! Most people don't like that.

Beat me to it.

iceracer wrote: Some progressive springs are simply to take up a given space and have a shorter stiffer spring. The Eibachs in my ZX2SR were like that, particularly in the rear.

I thought this was why as well. Kind of like a fancy dual spring combo but all in one wind.

fasted58 wrote: http://www.steeda.com/steeda-mustang-competition-springs-555-8241/

Thanks, but those are for 2005-2014. Mine's a 2001. :(

Spoolpigeon wrote: Linear rate springs are more predictable and the main reason I won't run a progressive rate spring. My theory is that the companies know their audience and the typical mustanger just drives in a straight line and wants that smooth ride quality.

I am on the other side of this. I vastly preferred progressive rate springs in my Porsche. They just seemed to work better then the similarly rated linear. HOWEVER i also got Koni shocks and struts valved by Koni specifically for the Eibach springs so that probably was a big contributing factor.

In reply to dean1484:

That's part of the issue for me. This car came with specially valved Tokico shocks from the factory. The car has low miles and I want to use those shocks with the new springs as well. So I need springs that will lower the car about an inch (its already 3/4" lower than a GT), provide a similar or slightly firmer spring rate, and be a linear spring like the OEM springs.

This isn't the best picture, but if you look at the wheel to fender gap, you can kind of see why I want to lower it a little.

It looks fine to me. That looks like perfect travel and gap for a street ride.

In reply to Brett_Murphy:

Well if it was your car you'd have nothing to be concerned about! Like I said, it's not the best picture. The car looks like a 4x4 in reality. Well no, I'm exaggerating, but trust me it really does need to lose about 1" of ride height.