Spring rates, how they differ and affect ride/application

Okay guys long post. Please school me here, really want to learn how these all affect ride, driving, turning, and drag and how to choose what you want and how each one differs and progressive and linear. I’ve seen one set where front is progressive and rear is linear then most are stiffer up front and softer in the rear (at least I assume 24lb/in is stiffer than say 200lb/in) correct me if I’m wrong. Best examples I can find are the BMR springs since they have a “drag” front (150lb/rear 160lb), “handling” (front 240lb/rear 200lb), and “street” (front 165lb/rear 160lb). I’m currently running SR springs which are progressive front (230lb/rear 200lb). They are very comfortable, not too soft but not too stiff and handle great. Haven’t done launches at a strip but doesn’t squat like the stocks did. What are the stock rates? I want to stay a 1.5” drop. I have BMR LCA’s and the relocation brackets and panhard bar. I’m looking for just 12’s in the ¼ even just a 12.99. I’m full bolt on with Lito tuning and I’ll be running the SVE drag wheel and tire set up with the skinnies up front as well. I’m used to the higher number up front and lower in the rear Ex: BMR handling springs which are 240lb/200lb vs the BMR drag springs which are 150lb/160lb. How do these affect ride, turning, and drag applications weight transfer left to right and front to rear? I was going autoX/road course route but now going more drag but it’s also a daily and I still like to do spirited driving and have fun turning. I know you WANT great weight transfer in 1/4 and keep it there. I’m going to be running strange engineering on all 4 corners so those should help as well correct. I want to keep 1.5” drop which is why I’m interested in the BMR springs. What will be different mainly between the “street” and “drag” springs? I remember how the stocks were and lots of body roll and weight transfer to the rear. Now they weren’t bad, I’d run if they were at the ride height I am now, just way too much 4x4 action there lol. But saying that, how do stocks compare to the BMR “streets” and “drag”? Do the shocks and struts play a role in how the ride is or mainly the springs? If say I had the BMR “drag” springs and I loved them in the ¼ but too soft around town with spirited driving, could I just stiffen up the shocks and struts and it would be more to my liking? Only rebound so nothing crazy to do to it. What exactly or how exactly does progressive work vs linear? I have an idea like progressive: gets stiffer as it compressed and linear is the same stiffness through the whole compression.

Thank you for all responses guys. Car is a 2006 FBO 3 valve.

Nontechnical late edit . . . your post isn't all that long, but it could stand being separated into a number of smaller single-thought paragraphs for easier reading and easier answering of the various questions.


Stock spring rates for the 2005 coupe are about 135 lb/in front and 142 or so out back. This from the MVMS document for the 2005 S197 that has lots of information. Most of it should apply to the 2006.

True progressive-rate springs do gradually increase their rate as they are compressed. But as a caveat here I think many of the springs being sold as "progressive" are actually closer to dual-rate where the change in rate happens rather abruptly when all the closely-spaced coils bottom out against each other at about the same time (same amount of spring compression).

The amount the rear of your car squats and the nose rises isn't a very good way to compare how much load transfer is happening when you swap from one set of springs to another. There's more than just spring rates that matter here, so it's really just a visual indication that some amount of load transfer is happening due to some amount of acceleration. "Nose dive" under braking and roll in the corners is the same thing, just different directions for the acceleration that causes whatever amount of load transfer.

Ride quality involves both springs (and bars) and shocks/struts. Crudely and for the range of spring rates available as "lowering springs", springs by themselves are more about 'firmness' and it's the specific shock or strut valving that's responsible for 'harshness' (too much damping) or 'floatiness' (if there's not enough of it).

Firming up shock and strut damping will not decrease how much suspension motion occurs, though doing so will slow the motions down slightly. Mostly, the car would feel more composed even though the amount of roll in any given corner would remain unchanged.

Progressive springs and dual-rate springs that sit in the soft rate region with the car at rest are probably going to be better for the dragstrip and for a softer/more comfy street ride. How much better, I don't know, but they'd let the nose rise a little more and resist squat a little better than fixed-rate springs whose rates are somewhere in between the firm and soft numbers.

Linears and dual-rate springs that don't get into the soft rate until the suspension has extended a significant amount (IOW, linear at the firm rate for most driving) are better for cornering & handling.


FWIW, I swapped my '08 GT from stock springs to BMR's GT500 handling springs (a little firmer than GT handling at 260/220) and found that Koni yellows have enough adjustability to find reasonable daily-driving settings. And that the settings can be a bit sensitive (but still better than not having any adjustment capability at all). I tracked the car (road course) on its OE springs and it was good enough on those that I'd have never bothered to swap them out if all I was going to gain was 30-ish lb/in. Not for that activity, anyway, and I don't need my car to be good at drag racing (let alone at the expense the corner-carving).


Norm

Norm, thank you on that! Really cleared some things up for me and helped me understand some more. Also thank you on the tip for the post lol. Will remember that for next time.

Also, just to clear up a possible misconception on how springs are "rated..."

A figure like 200lb/in means that the spring will compress one inch when 200lbs of weight are loaded onto it. In other words, the higher the number, the stiffer the spring. All bets go out the window with "progressive" springs, since that number thoretically changes the more you compress the spring. Thus for the first inch of travel the rate might be 120lb/in, then for the next inch it's around 200lb/in, and for the third inch, it's 350lb/in. Numbers are random, but it's an example. In reality, a properly engineered spring will show a curve when plotted with compression vs. rate. Most "progressive" springs that we see, though, as Norm mentioned, are really dual-rate, with a "soft" portion and a "hard" portion to the spring. Once the "soft" coils completely collapse (coil bind) they become infinite, and the "hard" portion is fully active. Sad thing is that most "progressive" lowering springs simply bottom out the soft bit once you take the car off the jack...

What you're really looking to do is "set up" the suspension, and to do that, there's a lot more involved other than just spring rate and damper curve. Do a google on "Instant Center" and on "Anti-Squat." Seems like most of the drag guys ditch the front bar and go to an INSANELY stiff rear bar, which is great for straight-line hard launches, but will let the car trip over it's own feet when it comes to a corner. Combine that with high %AS in the rear, and "90/10" shocks (very stiff compression, very soft rebound in front; opposite in rear, I believe), and you'll hook like crazy, but the car will flop around like a fish doing anything else.

In the end, you can have a great cruiser, a great corner-carver, OR a stright-line machine, but if you want to do more than one, you're into making compromises. So many of the setup choices you make for one are contraindicated for the others.

SoundGuyDave said:

Also, just to clear up a possible misconception on how springs are "rated..."

A figure like 200lb/in means that the spring will compress one inch when 200lbs of weight are loaded onto it. In other words, the higher the number, the stiffer the spring. All bets go out the window with "progressive" springs, since that number thoretically changes the more you compress the spring. Thus for the first inch of travel the rate might be 120lb/in, then for the next inch it's around 200lb/in, and for the third inch, it's 350lb/in. Numbers are random, but it's an example. In reality, a properly engineered spring will show a curve when plotted with compression vs. rate. Most "progressive" springs that we see, though, as Norm mentioned, are really dual-rate, with a "soft" portion and a "hard" portion to the spring. Once the "soft" coils completely collapse (coil bind) they become infinite, and the "hard" portion is fully active. Sad thing is that most "progressive" lowering springs simply bottom out the soft bit once you take the car off the jack...

What you're really looking to do is "set up" the suspension, and to do that, there's a lot more involved other than just spring rate and damper curve. Do a google on "Instant Center" and on "Anti-Squat." Seems like most of the drag guys ditch the front bar and go to an INSANELY stiff rear bar, which is great for straight-line hard launches, but will let the car trip over it's own feet when it comes to a corner. Combine that with high %AS in the rear, and "90/10" shocks (very stiff compression, very soft rebound in front; opposite in rear, I believe), and you'll hook like crazy, but the car will flop around like a fish doing anything else.

In the end, you can have a great cruiser, a great corner-carver, OR a stright-line machine, but if you want to do more than one, you're into making compromises. So many of the setup choices you make for one are contraindicated for the others.

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Thanks Dave,

Just looking for an all around fun car really. I'm not crazy wild about setting records. Just want to be able to head out to track once a month and drag or road course it for the fun. My main is focused on daily and drag since I won't road race it as much, but still want it to be able to handle a corner nicely if I want to have some fun daily driving. I plan on procharging it in the future. So will clearly get 12's then and 11's.

What you are looking for, is what we have in our SP009 Performance Spring Kit.

That spring kit provides a slight increase in wheel rate without "needing" a "high end" damper...has set records at the drag strip, and has also been used by many many people in road course and autocross applications (with the addition of upgraded sway bars and of course dampers).

Before we offered multiple spring solutions - the SP009 was all we had available. "Most" people were happy or content with them for all around duty....but the guys who chose to step it up a notch in the handling dept., naturally, wanted and needed more wheel rate. As a matter of fact, if my memory serves correctly SoundGuyDave used to use our SP009 Springs for handling. While he will tell you and I agree that he wanted and needed to go stiffer - I bet we will also mutually agree that they worked decently for what they are --- and definitely work better in a handling application than a stock height and rate coil spring set.

I say grab the SP009 spring set and enjoy. I have too many thousands of customers using them happily to suggest anything else. (unless of course you were strictly focusing on better handling)

BMR Tech said:

Before we offered multiple spring solutions - the SP009 was all we had available. "Most" people were happy or content with them for all around duty....but the guys who chose to step it up a notch in the handling dept., naturally, wanted and needed more wheel rate. As a matter of fact, if my memory serves correctly SoundGuyDave used to use our SP009 Springs for handling. While he will tell you and I agree that he wanted and needed to go stiffer - I bet we will also mutually agree that they worked decently for what they are --- and definitely work better in a handling application than a stock height and rate coil spring set.

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Yup, Kelly's got it right, I did use the SP009 (I think that was it, they offered two spring sets at the time, and this was the stiffer of the two), and "back in the day," it was pretty much "lowering springs" or "coilovers" for choice.

For an all-around, they're really not bad, particularly if paired with a decent damper (Koni yellows, for example).

FWIW, I think the rates on the SP009 are in the 160lb/in range; on my race car I'm currently running 750 front and 300 rear, but then I pee blood after hitting pavement expansion joints... ;-) Compromise!!

BMR Tech said:

What you are looking for, is what we have in our SP009 Performance Spring Kit.

That spring kit provides a slight increase in wheel rate without "needing" a "high end" damper...has set records at the drag strip, and has also been used by many many people in road course and autocross applications (with the addition of upgraded sway bars and of course dampers).

Before we offered multiple spring solutions - the SP009 was all we had available. "Most" people were happy or content with them for all around duty....but the guys who chose to step it up a notch in the handling dept., naturally, wanted and needed more wheel rate. As a matter of fact, if my memory serves correctly SoundGuyDave used to use our SP009 Springs for handling. While he will tell you and I agree that he wanted and needed to go stiffer - I bet we will also mutually agree that they worked decently for what they are --- and definitely work better in a handling application than a stock height and rate coil spring set.

I say grab the SP009 spring set and enjoy. I have too many thousands of customers using them happily to suggest anything else. (unless of course you were strictly focusing on better handling)

Click to expand...

That sounds exactly like what I'm looking for. Bit above stock but also a bit less than current but can do some drag stuff.