Spring rate misconception

[79T/Aman]

I've seen some wild statements regarding springs and rates, everyone seems to be fascinated with the rate.
First thing is to remember that spring rate is load over distance.
Second, no mater what the rate is the installed spring load will always be the same.
Spring rate is a useless number unless you know the wheel rate of a giver suspension system, (look it up there is not enough time to start down that road here)

Misunderstandings and wives tails.
The spring only has to be stiff enough to support the weight of the car! This is the most ridiculous statement ever put in print because it does not state at what distance of spring compression it should support the car.
Soft springs keep the tire in contact with the road better, this is missing a LOT of context and is VERY misleading.
Take a look at the Camaro picture bellow, at the time it had PTFB GT suspension kit on it but simply going to better tires caused more weight to be shifted and the result was front suspension collapse causing the rear to lift the wheel off the ground, the suspension was upgraded to PTFB race suspension.
What this shows is that the suspension must be tailored to the usage and applications and should not be decided on make belief. 

[NOT A TA]

But, but, but, that's such a cool pic Dave!

[scarebird]

I do not buy into this. 

My LS3 powered TA lost a minimum of 300 pounds off the front end vs the 400 Pontiac it had (car is 3,320 pounds empty).  Using 301 springs it still would shake your fillings out over rough roads.  I subbed in Moroso drag springs, 275# rate with half a coil cut off (so rate is a bit higher).  Car sits 1" lower than stock both ends and rides superb.

At the track, it faced a Camaro and Corvette - neither older than 5 years at the time and both powered by LS3's.  The Camaro bested my fastest once out of a dozen laps over 2 days.  The instructor drove the TA, pronouncing it "very well sorted out".

[JJ 109]

Cutting a spring down not change its rate.

[79T/Aman]

my experience spans 100s of cars, simple mat will show that a spring that light will bottom out.
"shaking the fillings out" tends to be an over the top abstract statement.

I don't buy loosing over 300# switching to an LS3 since the difference is only about 200#

Here is a customer's car with a Kaufman all aluminum Pontiac 461, it weighs about 404#, fiberglass hood, fiberglass inner fenders, aluminum hubs and calipers, lightened spindles, aluminum core support and radiator, aluminum bumpers and brackets, removed door bars, plastic door windows.
Granted it does have A/C full interior.

[79T/Aman]

Cutting a spring down not change its rate.

Yes but this is again something people wishfully focus on, rate increase can be estimated accurately in percentages, if you have a coil spring that is 10 coils and you remove one you will increase roughly 10% HOWEVER the first coil can be as much as 70% inactive therefore the rate increase from removing the first coil is between 3-5%
Now keep in mind that spring rate is not that relevant unless you calculate the WHEEL RATE !!! and on a second gen that is only about 30% !! (BTW this is where the 2:1 cut the spring 1/2 the amount of desired drop comes from but with 20% safety margined)
SO! lets use a 400# coil spring with 10 coils and you cut off the first coil it will shorten the spring about 3/4" to maybe 1" depending on the thickness of the wire and wire helix.
Back to our 400# spring with the first coil cut off, the spring is now 420# given 5% rate increase.
The wheel rate for our 400# is 30% =120#
Wheel rate for our 420# cut spring is = 126# as you can see 6# isn't going to do a darn thing to a car that weighs 3500-4000#

Now the softer the spring the longer it must be because it will need to be compressed more to support the weight put on it, as a result the number of coils is greater so if we go from a 400# spring with 10 coils to a 275 # spring with 12 coils you can see how removing the first coil nets about 4% increase at the coil, that is 11#  making the cut coil 286# with a wheel rate of 85# !!!!!

[scarebird]

Cutting a spring down not change its rate.

Not true at all:



Where k=spring rate; d=diameter of the spring wire; G=shear modulus of elasticity of the spring material (11,500,000 for a steel spring); D=mean diameter of the spring's coils; and N=number of active coils.

The spring rate (k) is normally measured in pounds per inch of deflection; for example, 100 pounds per inch. A spring having this rate will compress one inch under a 100-pound load. Two hundred pounds will compress the spring two inches, three hundred pounds will compress the spring three inches, and soon. This relationship will also be exhibited when the spring is extended rather than compressed.

my experience spans 100s of cars, simple mat will show that a spring that light will bottom out.
"shaking the fillings out" tends to be an over the top abstract statement.

I don't buy loosing over 300# switching to an LS3 since the difference is only about 200#

Your experience has not driven/raced this car. 

The 300 pound difference is more than the engine; the previous drivetrain was a 403 with TH350, AC, PB, PDL, PW etc. and a much heavier bumper assembly vs. a much lighter AC compressor, manual brakes, lighter nose, battery in trunk. 

I drive this car hard - it has yet to bottom out that I have noticed.

[79T/Aman]

Not looking to have my thread turned into a one man rebuttal.
The blue Camaro I posted had 600# front springs when that picture was taken 3 years ago!! we are now at 800# and winning more races.
Picture below is Mike's blue Camaro after winning the Nashville good guys as well as the shout out not the 2 plaques on the windshield, the other Camaro came in second also with PTFB suspension.

[79T/Aman]

  "Your experience has not driven/raced this car. "
Sorry but a second gen is a second gen, unless something DRASTIC was done to it it is not significantly different than any other, you have removed weight, so have we (a 77 T/A ) I posted the reading of the scale, explained what was done to it, it is still a street driven car, full interior, Hooker show bar full compliment of PTFB chassis bracing, fiberglass hood, inner fenders. Aluminum 461 Kauffman Pontiac, core support, radiator, manual master, hubs, shocks, TKO600 10 bolt rearend, PTFB Comp leafs, stock fuel tank, door beams removed, side lexan windows, "racing" seats, That car uses 800# front springs and we can bottom the suspension on the bump stops!!!
SORRY but your 275# springs are not holding up that car.
BTW we are going to 1000# springs for this year.

[scarebird]

I am happy for you and Mike. 

800# springs would not fare well on New Mexico roads, or any roads in reality - pure track stuff.

I believe Herb Adam's approach is superior to Dick Guldstrand's.

"SORRY but your 275# springs are not holding up that car." 

Rubbish - your preconceptions are blinding you here.

[79T/Aman]

  "your preconceptions are blinding you here."

I guess it's a good thing that preconceptions win races.
Need to checkout the roads in In, Pa, Oh, Il sometime where the freezing and thawing turn roads into washboards.

[rkellerjr]

So, this all looks fascinating but beyond my understanding, can someone explain to me what some of this means. I'm curious and wanting to be educated but I don't understand the math vs the car vs spring #'s, etc. Sorry to be an amateur and interested in what your talking about.

[79T/Aman]

So, this all looks fascinating but beyond my understanding, can someone explain to me what some of this means. I'm curious and wanting to be educated but I don't understand the math vs the car vs spring #'s, etc. Sorry to be an amateur and interested in what your talking about.

Basically trying to give a basic understanding of springs and how they affect your car, I did the math to show that spring rate is not the end all be all and that cutting springs will not increase spring rate as much as people think.

Scarebird may want to hear me out here.
Herb Adams' name has already been thrown around, ( I know Herb and Matt, I even have a business relationship with them)
Herb advocated cutting the stock 420# springs, wich have 8 coils so cutting the first coil would put you at around 450# NOW Herb also talks about the function of the JOUNCE BUMPERS (bump stops) actually a secondary spring as part of the suspension.
Then Herb added a MASSIVLY stiff sway bar. a sway bar is nothing more than a torsion spring folks!!!!
SO in the end this so called soft spring set up is not so soft is it?
All this was relatively adequate for a street car with 15" tires and tall sidewalls, modern tires with short stiff sidewalls have very little slip angle compared to 15" high side wall tires, this in turn shifts mass much more quickly soft tires will absorb much of this mass shift giving time for the spring and sway bars to react.
Springs are active, sway bars are reactive. Even large sway bars will not help slow down the mass shift, but a stiffer spring will as it is active HOWEVER if the spring is soft it need to compress more to support the mass shift, as the suspension moves now the sway bar comes into play trying to assist the spring.
As far as Scarebird calling my information "rubbish" here is my take on his situation.
Quick back ground, I pit crewed on stock cars ARCA, NASCAR we used to us too soft rear springs and allow them to coil bind on the high banks (that's why it was easy to spin in turn 4 because you would have a sudden transition into over steer)
His front springs are so long and soft that he is running the spring into coil bind not his 275 rate spring could be 500,600,700 # who knows what it is.
If Herb Adams explained that the jounce bumpers were designed and expected to come into play with 450# springs does anyone believe they would not be in play with 275# springs????????????????
In my other post I posted a picture of evidence of coil bind and that is a 350# spring!!

Trying to help people make an educated purchase decisions, and set up their cars, not "rubbish preconceptions"

[nas t eh]

I am happy for you and Mike. 

800# springs would not fare well on New Mexico roads, or any roads in reality - pure track stuff.

I believe Herb Adam's approach is superior to Dick Guldstrand's.

"SORRY but your 275# springs are not holding up that car." 

Rubbish - your preconceptions are blinding you here.

You are forgetting that Herb Adams explained why cutting a coil off a spring will effectively increase the springs working rate. He said that Pontiac engineers got it wrong with the WS6 springs as they though the purpose behind his(Herbs) cutting coils in his race cars was to increase rate, but he only wanted to lower the car, the increased rate as a result of cutting the coils was an unintended byproduct.


The rate increase comes because less coils in the same installed space causes the remaining coils to expand into the space and stand up more vertically the have better leverage(mechanical advantage) on carrying the load. A straight rod standing up in the coil pocket is the ultimate stiff spring.

[jonathonar89]

I do not buy into this. 

My LS3 powered TA lost a minimum of 300 pounds off the front end vs the 400 Pontiac it had (car is 3,320 pounds empty).  Using 301 springs it still would shake your fillings out over rough roads.  I subbed in Moroso drag springs, 275# rate with half a coil cut off (so rate is a bit higher).  Car sits 1" lower than stock both ends and rides superb.

At the track, it faced a Camaro and Corvette - neither older than 5 years at the time and both powered by LS3's.  The Camaro bested my fastest once out of a dozen laps over 2 days.  The instructor drove the TA, pronouncing it "very well sorted out".

darn, 275lb is pretty light as I know PTFB, DSE, Hotchkis, Viking and others usually set people up with 450lb-600lb rate depending on the situation for LS swapped cars.

[firebirdparts]

I am not into your business, so I never talk to people about this, but I can certainly imagine that it's hard.  I just have not heard much about this (in my mind, the discussion I try to avoid is torque and horsepower, ha ha).

They made us study engineering mechanics in school, and being a car guy who grew up on a farm, I was interested.  So I feel like on paper I get it entirely.  Springs are super simple, thank goodness.   What's not simple is the relationship between the spring and everything else, at least in a double wishbone suspension.  Roll center, for instance, is not a simple concept.  The forces smashing that spring in a turn are coming at the car in three dimensions and of course momentum plays a big role in that, so it's really 4.

[79T/Aman]

I am happy for you and Mike. 

800# springs would not fare well on New Mexico roads, or any roads in reality - pure track stuff.

I believe Herb Adam's approach is superior to Dick Guldstrand's.

"SORRY but your 275# springs are not holding up that car." 

Rubbish - your preconceptions are blinding you here.

You are forgetting that Herb Adams explained why cutting a coil off a spring will effectively increase the springs working rate. He said that Pontiac engineers got it wrong with the WS6 springs as they though the purpose behind his(Herbs) cutting coils in his race cars was to increase rate, but he only wanted to lower the car, the increased rate as a result of cutting the coils was an unintended byproduct.

Who is forgetting?
I know that I explained the coil cutting principal and also explained how cutting the first coil does not have as much effect on rate increase as up to 70% of the first coil is inactive, further more Herb explained how to heat up just a couple inches of the end of the coil and flipping it upside down to flatten the spring end making the end into more of a tangent rather than a pig tail end.         

Quote
"The rate increase comes because less coils in the same installed space causes the remaining coils to expand into the space and stand up more vertically the have better leverage(mechanical advantage) on carrying the load. A straight rod standing up in the coil pocket is the ultimate stiff spring."

These are the confusions I am trying to address,
"The rate increase comes because less coils" that is correct BUT on a car the lower control arm is not fixed therefore the spring does not expand to take up into a fixed dimensional space, the lower control arm moves to close up the space and compress the spring until it reaches the load rate equivalent to the weight of the car being exerted upon the spring.
The coil spring wire only will stand up more vertical because the is less over all length of wire and that is what increases the rate but that change amount is so minimal that it can't be taken into account and spring rate is not measured under load because the pitch of the coil helix varies.

[79T/Aman]

Here is the thing I guess is not working is that no one wants to try to spend the time to read and understand, they would rather give their 2C and blanket statements, here is what I see so far:
-People want to make spring rate the end all be all without understanding the mechanical function of the suspension even though I explained that spring rate should not be the focus, wheel rat should be.
-People want to make correlations between various things that they don't understand yet have nothing to do with each other, as an example(this goes against what I just mentioned but it seems this is the only way to get through)
-I hear such things as 700-800# springs ???!!! it will rattle my teeth, kill my kidneys, ride like a chuck wagon...on and on it goes!!
 now if I told you that from the factory some 3rd gen T/As used 720# springs! and a V6 Ford ranger uses an 800# spring!!   

I guess I wish there was an easier way to explain as much as possible without having to write such long drawn out paragraphs, but there is so much to explain and most can't clear their heads of the things they have read in the past, turning it all into a mental soup.

[firebirdparts]

Well, maybe some examples would be better.  if you are sticking to a few control arm geometries, or in our case here at TAC we stick to one, the 70 Camaro.  If you say that you recommend X for a street car and Y for "Pro Touring" and it's not that simple for competition, I think it would be hard to argue with that if all the weapons I had were some boring platitudes.  If I have my car the way I like it already, then I don't need to argue.

[79T/Aman]

Well, maybe some examples would be better.  if you are sticking to a few control arm geometries, or in our case here at TAC we stick to one, the 70 Camaro.  If you say that you recommend X for a street car and Y for "Pro Touring" and it's not that simple for competition, I think it would be hard to argue with that if all the weapons I had were some boring platitudes.  If I have my car the way I like it already, then I don't need to argue.

Sorry I,m not understanding the post.
- Examples were provided multiple times.
- This applies to modified street cars to race cars.
- "control arm geometries" control arms don't change the geometry unless they are made shorter or longer.
- 70 Camaro ??
- No argument here, trying to give good info based on some of the things I've read that were less than accurate.