progressive vs. linear springs;

Which are better and why ? Which company do you guys recmd ? I only care for track use.

These will be for my KW Clubsports.

 

for strictly track... Linear.
Reasons:
Easier to produce and can be made to lower a car beyond the point of progressive rate springs.
Easy to work with, because the spring rate never changes, allowing quick chassis set-up
Inexpensive, allowing most race teams to use several different sets depending on track conditions.

For all-in-one solution: progressive

 

Which company do you recm in getting lienar springs from ? I'm thinking swift springs..

 

i thought KW systems come with springs?... I haven't had personal experience with Swift but have used HR and Eibach race springs

 

They do but in progressive... 450 front and 1050 rear... i'm looking for either 600 front 800 rear or close to 800 front and 1000 rear.

What do you recm for tenders ?

Thank you for all your help.

Enrique

 

It's probably best to contact KW to make sure the shocks can work with the spring rates you want. There are many variables to consider.

 

I did.. they weren't to helpfull. :/

They said the 450 front and 1050 rear will be very good with my hoosiers. Although they are progressive they said i will be surprised how good the car will handle. Others on a more road racing track forum have expressed to another person whom had v3 that 450 is not enough for the front although kw said that will work. hmm..

 

Enrique.. Use Eibach Pro linear rate springs.. Absolutely what you need for track use, that's what I have, make sure it's the PRO version you get. It's what Kevin Buckler (The Racer's Group) uses on his Cup Cars and his ALMS Cars, they won Le Mans and 24 Hours of Daytona on them...

Anything more than 600 front/800 rear will be way too much for any street use and will also be too much for Sears Point.

Cheers, Graham.

P.S. Saturday Lunch at Alice's Restaurant? around 1:00 P.M.?

 

I'm glad you chimmed in Graham. I was thinking of txting you earlier and asking for your opinion. I will take your suggestion rumor is your car very well setup from what birds chirp into my ears

I'll be at Alices.. hmm i'll email tony and mike see if they want to come.

 

Penske race springs, the best but also very $$$.

 

higher spring rate does not equal better times.... always a compromise. on really smooth tracks you want hard up to a certain point.
For bumpy tracks, softer is often better.

 

Would you please expound on this? How does a person calculate the proper spring rates for a 996TT?

 

If a specific Car weighs a certain amount, then there is a range of spring rates that will work optimally for that Car. All springs do is support the weight of the Car.. the dampers control all the movement of that weight. The spring rates are chosen depending on what the Car is used for, the suspension geometry, ride height, aerodynamic characteristics etc.

If you talk to the spring tech's/gurus, you will find that they have charts that specify a given range of spring rates for certain applications and weights... Obviously, a 4000 lb Car will need different springs than a 2000 lb Car.. Likewise, our Porsches need a mismatched set of springs because of the rear weight bias.. The 996 Cars act like a 4000 lb car at the rear (4000 lbs /2 = 2000 lbs and like a 1500 lb Car at the front (1500 /2 =750 lbs).. (if you corner balance your Car, you will find that the rear axle weighs (on my GT2) approximately 1000 lbs per side, for a total of 2000 lbs at the rear.. my front only weighs about 620 lbs per side, for a total of 1240 lbs at the front) so unlike a Car that has 50/50 weight balance that might have almost identical spring rates front and rear, we have rates that range from 200 lbs apart, up to 400 lbs apart or more.

Chosing an actual rate for our Cars depends a lot on what you want to do with it.. Very soft rates (200 -250 lbs front and 350-400 lbs rear) will let the Car ride very smoothly and with the right dampers it will soak up bumps like a Lexus, but will get all wobbly and mushy in the corners and on the track and it might allow the shocks to travel TOO far and hit the bump stops. Too stiff (1000 lbs front and 1250 lbs rear) will make the car brutally harsh on anything other than a billiard table smooth track.. it also reduces the amount of travel that the shock goes through, because there is not enough weight to compress the spring to its maximum and this is bad, because the shocks are designed to operate through a given "stroke".

On a rough track with sharp bumps, you want a slightly softer spring rate to soak up the bumps and let the shocks, tires and springs work together to absorb as much as they can, without being too soft and sometimes choosing a slightly higher ride height helps at a bumpy track, to allow full suspension travel; otherwise, with too high a spring rate your Car will literally leap off the road and launch itself over those bumps.. this is sub-optimal. With softer springs and higher ride height, some of the downsides are more pitch front to rear, more squat under acceleration, more nose dive under braking and more weight transfer side to side (which can sometimes be good) and a higher roll center/center of gravity due to increased ride height.

On a smooth track, a higher spring rate is used, because there are fewer bumps and the Car can be set up lower (which helps aero and lowers the roll center and center of gravity). Higher spring rates also allow less pitch, less squat at the rear under acceleration, less nose dive under braking and less weight transfer side to side all of which keep the Car more stable under the dynamics of the track.

Aero has to be taken into account with REAL race Cars.. A friend of mine has a couple of Porsche 962's.. they run 4,000 lb yes four thousand pound springs on each corner (16,000 lbs of overall spring rate), because they generate 10,000 lbs+ of aerodynamic downforce at speeds over 150 mph.. so the spring rate HAS to be able to support that weight plus the relatively measly weight of the Car (2500 lbs or so).

This also brings up the progressive vs. linear question... Progressive springs have a rising rate, they are softer through their initial inch or so of travel and then get stiffer the more you compress them. Linear springs are the same rate throughout their compression. Linear springs are much better for the track, because they are consistent and can be more easily tuned for.. progressive rate springs need to be thoroughly matched to their dampers, which ideally would also have a progressive rate of damping to match the progressive rate of the spring... VERY hard to do if you need to adjust your suspension for various tracks.. easier if you are a Car Manufacturer with a fixed set of non-adjustable dampers that can be built to match a progressive spring in a sedan.....

To correctly match a spring rate to your Car, you need to work together with the manufacturer of your dampers, since they know the damping curve of their damper and will have a list of springs that match that curve through the damper's range. Matching springs for our Cars is quite difficult, because you have to take the weight at each end and allow for 2000 lbs/ 1250 lbs accelerating and decelerating up and down at a certain set of rates/speeds (2000 lbs multiplied by # of inches per second (velocity)) generates a TON more force than 1250 lbs multiplied by # inches per second, so that's why the rear springs HAVE to be a heavier rate than the front.. they have WAY more "weight" (actually weight multiplied by the accelerative forces applied during high speed driving) to control. The manufacturers of the springs have in theory tested all of this and "should" know what they are talking about when it comes to helping you choose the correct spring for your Car...

Obviously swaybars are a BIG part of this whole equation as well...

Sorry that was so long...

 

good write up! Thanks for the info

 

+1 on the write up