Progressive Vs. Linear Rate

[spetz]

Which one is better?

I have progressive rate Fulcrum coilovers in my car and I am thinking of swapping to D2 Coilovers mainly for the damper/rebound adjustability and order them with a softer spring rate for more street oriented suspension.

So what is the go? I have always thought that progressive suspension is better because you start off soft and once there is more pressure they stiffen up.

Also, is there a way to calculate the best spring rate of a car given the front/rear weight distribution?

[spetz]

These are my springs rates:
What do people think of them for a street car?

Front spring rate 220-260 lbs/in Progressive
Rear spring rate 170-220 lbs/in Progressive

Damper rates (measured at 600mm per second)
Front bump rate 1000nm
Front rebound 3000nm

Rear bump rate 850nm
Rear rebound 2750nm

Valving design is linear to digressive.

[PhatSol]

What is the conversion from lbs/in to kg/mm?

[wynode]

I think this belongs more in the technical forum. Moved.

[J_Mech]

Certainly is spetz, it actually depends on a few things, but mainly how much stiffness you can handle in terms of comfort and how much roll you can afford during cornering. Actually a lot of the harshness can be removed by adding anti-roll bars in the system while removing some spring rate for comfort. You were spot on in giving the damper rates, damping is just as important in the grip and comfort levels.

I would reccomemnd first posting up the weight of your car and the % front to rear weight distribution, then people (and me) can start number crunching. Any chance of the original rates?

J_Mech

phatsol, divide the lbs/in by apprx 56, will get you to kg/mm.

[spetz]

The original rates to my knowledge are 120 lb front and 89 lb rear. Although I read different ratings from different sources.

As for car weight. Ok a coupe lancer like mine is supposed to weigh 990kg.
I am unsure of weight distibution yet :(
When I get my car back I'll get that checked.

But, over the 990 kg it has bigger brakes, strut braces front, rear, upper and lower, FTO V6 engine with FTO gearbox in it, bodykit, 16" wheels and a stereo which doesn't include amps of subs.

Looking at the spring/damper rates, how does this look for street for a car roughly 1100kg?

[J_Mech]

I assumed 1100kg and 65% front weight, and a whole bunch of other things. The progressive springs alone, compared to the originals will halve the roll rate (even more with the progressive factor). If you dont mind the fairly stiff ride (basically double the stiffness) it will be a much flatter ride (high performance sportscar/ racecar roll rate values), id opt for softer springs, larger antiroll bars personally (bit easier to have as a daily driver).


I like the sound of progressive as well, when your not going hard you keep within the softer range of the stifness = comfort, and use it when you need to. It also tends to move the stiffness towards the rear for handling characteristics with these springs mentioned (like adjusting a rear anti-roll bar stiffer) during the progression from initial stiffness to final stifness. Havent looked at damping yet.

J_Mech

[spetz]

Thanks for that ;)
Any more info would be greatly appreciated!

PS. I am more interested to find out how this setup will go over bumps etc. Stiffness isn't too bad as I don't go on any really bumpy roads and I live in ACT which has smooth roads compared to other states

[spetz]

Ok I got my car weighed.

These are the results:
1120kg
Front weight 740kg
Rear weight 380kg
This gives a weight balance of 64/34

Car was measured with about 20 litres of fuel, no spare tyre, without me or passangers in the car.
Increments were 20kg on the scales.

Other info on what spring rates are on the car (and standard ones) are above.

Swaybar sizing is 18mm front and 18mm rear (front SHOULD be 21 or 22mm, I don't know why this is).
However I am dedicated to a great handling street car so custom swaybars or any other suspension work is not a problem.

My main priorities is street handling. So obviously nothing too stiff, this isn't for discomfort but rather so it doesn't skip/jump off of bumps.

Shock rate is also not important as I am getting the Tein super streets which are adjustable.

Any info would be greatly appreciated!!!

[J_Mech]

There is a rule of thumb when calculating front to rear spring rates, and it includes the weight of the car, basically you convert to chassis natural frequencies. I only took the averages of the spring rates you got there, it looks about right, possible a bit higher on the rear to get more ratio in the back. Overall it looks on the high side for comfort.

It all depends on the type of tyres your running, you dont need much roll resistance (bar or spring) if your tyres cant generate the G's to roll your car. I would just start off with springs that are about right (something you can live with all day) then add anti-roll bar (go the adjustables) until you get the desired roll rate. Additionally use the bars (front and rear) to adjust handling. Not sure about why from 18mm to 22mm on the front, will increase the overall roll resistance, but it will be increaseing the grip at the back (loosing front end grip), thats ok if the front had too much to start off with, if it was understeering, its just going to understeer more.

Probably dont need to go to a custom bar, you'll find a few adjustable ones out there that should be able to give you enough.

Damping is important, there is a difference between the best grip setup and the best comfort setup, comfort one being on lower settings. From the numbers you gave they look high, aimed at grip, rear is probably a touch high.

[Limbo]

progressive are only good if they are design for that car with those shocks.
Otherwise they could be worse for the car.

Main reason is the are usually softer then become harder at a certain point. If you shocks are not helping or if the car is the wrong weight then the initial softness designed for confort will end up screwed up.