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914World.com _ 914World Garage _ Progressive VS Linear Rate Springs
Posted by: Aaron Cox Feb 8 2005, 11:58 PM
i have opinions of both.....
i run linear 140's..... a friend of mine has progressive 165's.
what are the pros and cons of each.
Posted by: MattR Feb 9 2005, 12:01 AM
im not your friend
Posted by: rick 918-S Feb 9 2005, 12:04 AM
| QUOTE (MattR @ Feb 8 2005, 10:01 PM) |
| im not your friend |
Posted by: MattR Feb 9 2005, 12:04 AM
dont get all emotional aaron.
okay, so my understanding is progressive springs apply an exponential force rather then a linear force. Basically the spring constant changes during load. So when you're in a turn, instead of bottoming out the suspension, you're adding more spring rate. The advantage is the car is smoother and doesnt oscillate when there is no significant load on the suspension, but under load (in a turn) the suspension stiffens up.
Posted by: nebreitling Feb 9 2005, 12:07 AM
do you like your spring rates -- and therefore handling -- to change as you dive deeper into a turn?
then progressives are for you.
linear all the way...
Posted by: Aaron Cox Feb 9 2005, 12:07 AM
but the exponential curve of the spring rate isnt easy to predict..... unpredictable corner load = unpredictable handling
| QUOTE |
| do you like your spring rates -- and therefore handling -- to change as you dive deeper into a turn? then progressives are for you. linear all the way.. |
EDIT: thats right, power to nate dog!
Posted by: MattR Feb 9 2005, 12:08 AM
Well dont your forces increase as the tire patch is taken toward the limit? There is nothing linear about a tire patch, or body roll, or slip angles. Those are all exponential functions, so why arent your springs?
Posted by: Aaron Cox Feb 9 2005, 12:13 AM
body roll with progressive springs in exponential....
body roll with linear springs is linear 
Posted by: MattR Feb 9 2005, 12:15 AM
you have a sway bar, right? a big ass tarret one. That is most definatly not a linear progression.
Posted by: nebreitling Feb 9 2005, 12:16 AM
i don't know how much all this exponential vs. linear stuff sums up the argument. i'm totally willing to concede that *everything* is exponential....
but, in my very humble experience (ie. driving only 1 914 w/ progressives vs my linears), validated by people who have forgotten more than i'll ever know, driving a car at the limit is more predictable on linears...
look at generic race springs: all linear.
Posted by: Aaron Cox Feb 9 2005, 12:16 AM
| QUOTE (MattR @ Feb 8 2005, 11:15 PM) |
| you have a sway bar, right? a big ass tarret one. That is most definatly not a linear progression. |
its a torsion bar..... thats all it is.... effective spring rate doesnt change....
and i have no body roll
Posted by: Brett W Feb 9 2005, 12:16 AM
Progressive rate springs are springs that get stiffer per inch of compression. They tend to be nice for squishy production cars that like a nice ride but need to keep from knocking the mirrors off if any hard conering occurs. They give a very good response to mild frequency bumps. Making for a nice ride on rough streets.
For a performance car stick with straight rate (linear) springs. they will have the same characteristics throughout the range of motion. Your car will take a predictable set in the corners as opposed to rolling a lot and then settling down on the heavier rates.
Linear rates will tend to act like rising rate springs due to some mounting considerations. When the spring is mounted directly over the axle and axle travel is purely vertical you get a linear rate. But when Motion ratios are introduced, when the wheel moves at one rate and the springs operate at another, you in effect create a variable rate spring. Variable rate springs can bring another variable into suspension tuning, which is very hard to deal with.
Coil springs and leaf springs are the only ones that lend themselves to rising rates. In our case coils are the only ones to be concerned with.
Posted by: JOHNMAN Feb 9 2005, 12:19 AM
My opinion about the progressive coil springs is that for the first amount of travel, the spring is softer than the last amount of travel.
I had a set of "progressive" springs and didn't like the way the car reacted. The first inch or so of travel was soft and became progressively firmer just like I would expect, but I didn't like the fact that you had to "set" the car before it would really feel stable.
I went to linear springs and like it much better. The first inch of travel is almost just like the last. (good to the last drop) 
I think that the way they make those progressive springs is that the "soft" part of the spring has the coils spaced further apart, while the "firmer" portion has the coils spaced closer together. (that might be backwards.....)
In any event, I don't like the variable spring rates in a performance application.
On bumpy streets, however, it might be a good thing.
Posted by: lapuwali Feb 9 2005, 12:20 AM
Pretty much, that's it. You can run a softer initial spring rate, but a compressed rate that's stiff enough to prevent bottoming. Note that linear rate springs don't always translate to a linear spring rate at the wheel. If the spring axis is tilted significantly wrt the plane of suspension movement, the rate will naturally change as the suspension compresses. On the 914, the axis of the spring is more or less in line with suspension movement, so the rate is reasonably linear (on the rear, of course).
Gas-charged dampers also often provide some springing action in compression, so the damper also has to be factored in when discussing wheel spring rate. This rate is always exponential. There have been "dampers" which had air or nitrogen cells in them that provided 100% of the springing. Rubber springs also provide a non-linear springing effect, and quite a few cars rely on compliant bumpstops when cornering to provide some springing.
It's not at all difficult to get used to spring rates that "change" mid-corner. As noted, the tires (which are also part of the spring system, and being pneumatic, are exponential springs) provide a significant spring effect.
In short, pure linear springs do not exist on real-world cars.
Posted by: MattR Feb 9 2005, 12:21 AM
Squishy for production cars? Cars create oscillations that unsettle the car. If your car is sprung too tightly ( 
) it will literally bounce under acceleration and at the top of the sin curve it will lose an amount of grip that is proportional to the amplitude of the oscillation.
Posted by: lapuwali Feb 9 2005, 12:24 AM
| QUOTE (nebreitling @ Feb 8 2005, 10:16 PM) |
| look at generic race springs: all linear. |
Horses for courses. To some extent, it's a "feel" thing, and some people like non-linear springs, even in racing applications. Racing applications don't dictate everything I do, and shouldn't for you, even on the AX course. Road-racing is the not the same as AX, which isn't the same as street driving, as I'm sure you know.
Posted by: MattR Feb 9 2005, 12:25 AM
| QUOTE (nebreitling @ Feb 8 2005, 10:16 PM) |
| look at generic race springs: all linear. |
is that really true? how can i verify that?
Posted by: nebreitling Feb 9 2005, 12:27 AM
| QUOTE (lapuwali @ Feb 8 2005, 10:24 PM) | ||
Horses for courses. To some extent, it's a "feel" thing, and some people like non-linear springs, even in racing applications. |
point conceded.
Posted by: Aaron Cox Feb 9 2005, 12:28 AM
for street: gimme progressives..... nice ride
for AX: gimme something that is predictable in corners...... always the same throughout the corner.....
Posted by: Aaron Cox Feb 9 2005, 12:30 AM
| QUOTE (nebreitling @ Feb 8 2005, 11:27 PM) | ||||
point conceded. |
comes down to feel
Posted by: Mueller Feb 9 2005, 12:39 AM
| QUOTE (Aaron Cox @ Feb 8 2005, 11:16 PM) | ||
its a torsion bar..... thats all it is.... effective spring rate doesnt change.... and i have no body roll |
the swaybar does act as a spring and it does affect the ride of the vehicle....unless you drive on perfectly smooth roads so that both sides of the bar travel up and down at the same time....being in the real world, that is not the case
the rate of the swaybar does change corner to corner and changes with the differential of wheel movement from side to side....a bar set on firm is going to have a worse ride than a bar set on soft........
Posted by: bondo Feb 9 2005, 12:48 AM
| QUOTE (Mueller @ Feb 8 2005, 11:39 PM) | ||||
the swaybar does act as a spring and it does affect the ride of the vehicle....unless you drive on perfectly smooth roads so that both sides of the bar travel up and down at the same time....being in the real world, that is not the case the rate of the swaybar does change corner to corner and changes with the differential of wheel movement from side to side....a bar set on firm is going to have a worse ride than a bar set on soft........ |
The rate also changes based on how far the sway bar "arm" is from horizontal. If you're twisting the bar such that it's 45 degrees from horizontal (I know, it'd never be that much, this is just an extreme example) then it'll be at a different rate than when the arms are horizontal.
Posted by: trekkor Feb 9 2005, 12:49 AM
| QUOTE |
| a bar set on firm is going to have a worse ride than a bar set on soft........ |
Or in my case, a better handling car which allows me to drive faster than most...Muhahahahahaaaa.
KT
Posted by: nebreitling Feb 9 2005, 12:53 AM
| QUOTE (trekkor @ Feb 8 2005, 10:49 PM) | ||
Or in my case, a better handling car which allows me to drive just barely faster than most horse-and-carriages, but not nearly as fast as nathan. he's really fast....Muhahahahahaaaa. KT |
thanks trekkor!
Posted by: trekkor Feb 9 2005, 01:02 AM
O.K., This is really wierd
Posted by: SirAndy Feb 9 2005, 01:22 AM
| QUOTE (Aaron Cox @ Feb 8 2005, 10:07 PM) |
| unpredictable handling |
that's what i heard too.
unfortunately for you, i'm running 180 *progressive* springs and i very much like the way the car handles.
contrary to popular belief, i'm having *no* problems predicting the cars handling ...
Andy
Posted by: redshift Feb 9 2005, 01:49 AM
I must have installed my progressive springs upside-down, they get stiffer when the car is going straight, then the get lax in the turns, when my car rolls over, and begs you to rub it's belly.
M
Posted by: Marv's3.6six Feb 9 2005, 04:26 AM
One of the more recent trends in damper technology is to run linear springs with "position sensitive" dampers. These dampers are very tuneable. You are able to tune the absorbtion rate at various positions of the damper stroke.
At the minimum these dampers have adjustments for initial or beginning rate and ending rate. The ending rate is used to slow the stroke of the damper as it nears "bottom out" in effect making the damper "progressive" in action. 
Posted by: ArtechnikA Feb 9 2005, 05:58 AM
| QUOTE (MattR @ Feb 9 2005, 01:21 AM) |
| If your car is sprung too tightly it will literally bounce under acceleration... |
you mean -- if your car is underdamped ...
more spring means you need more damping; they go in pairs.
Posted by: trekkor Feb 9 2005, 09:22 AM
| QUOTE |
| and i have no body roll |
me neither...
KT
Attached image(s)
Posted by: trekkor Feb 9 2005, 09:26 AM
REALLY flat... 
Attached image(s)
Posted by: TimT Feb 9 2005, 09:46 AM
| QUOTE |
| look at generic race springs: all linear. |
actually some ground effect cars used progressive springs, the 956, and 962 come to mind
Posted by: Mueller Feb 9 2005, 10:08 AM
Hey Tim,
are cars with tender springs considered progressive or linear?
Posted by: Aaron Cox Feb 9 2005, 10:29 AM
since i have dialed in more swaybar trekkor
Posted by: slivel Feb 9 2005, 12:07 PM
| QUOTE (Mueller @ Feb 9 2005, 08:08 AM) |
| Hey Tim, are cars with tender springs considered progressive or linear? |
The answer depends on whether or not the tenders are in coil bind with the car in a static condition weight on wheels condition. Some people call this arrangement "keepers" and "tenders" are springs that actively work dynamically. In my case I just went to progressive rate spings on the racecar after 5 years of linear rate. I have only one test day for data but the car felt a little better to me in the high speed sweepers at Willow Spriings. My front set up is progressive rate 161-450. I achieve this by stacking a linear rate 450 and a progressive rate tender of 250-625. I also have the stacked set-up on the rears - currently 125-250 progressive. Most modern Porsches with triple adjustable shocks at the track seem to be using tenders. I don't know how many are just "keepers" to prevent spring droop when the car is jacked up or if they are active working springs when the suspension is working. On my set-up the tenders go into coil bind and the rate becomes linear after about 2 inches of shock travel. Next race is at Phoenix on the weekend of 19 Feb so I'll have more experience with progressive rate spings and be able to give you guys some more feedback.
Steve
Posted by: TimT Feb 9 2005, 01:35 PM
| QUOTE |
| are cars with tender springs considered progressive or linear? |
2 linear spring equals a linear progression.
Those little tender springa are pretty insigificant anyway. They collapse with such little pressure. They are mainly to hold the spring in line with the perches
Eibach is making spring sets with what looks like a tender spring, but is really a short progressive spring. You can get multiple progressive, progressive linear sets etc. Get the Truechoice paper catalog, they have a pretty large selection of springs and some explanations
Posted by: groot Feb 9 2005, 02:11 PM
I believe many racers use linear rates springs because they are cheaper and it's easier to buy several sets of them (me included). I use my jounce bumpers to add some progressiveness to the setup. Also, a compliant ride (a primary benefit of the progressive spring) is not critical to a race car. Everything's a compromise.
You want the rate to go up towards the end of your travel to prevent bottoming out. If a vehicle bottoms out, the loads are simply astounding. Using jounce bumpers means you can run a reasonable rate spring that allows some suspension travel and then count on your jounce bumpers to dissipate the energy, in case you excede the energy your spring can sbsorb.
There's a reason many (maybe all) production cars use progressive springs. It's much easier to get a compliant ride and attempt to control the energy with the limited travel available in today's vehicles with a progressive spring. OEMs also spend a lot of time and energy developing/tuning jounce bumpers because they cannot get enough energy dissipation from the spring alone.
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