Progressive vs. Linear springs - Nissan 350Z Forum : 350Z / 370Z Tech Forums

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Old 05-31-2006, 03:10 PM   #1 (permalink)
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Which are better and progressive springs (Eibach) or linear springs(hotchkis). I really don't know the difference or the effects of each. One more thing i know the Z, maybe the '06 changed but usually the springs rate is higher on the rear than on the front springs. The hotchkis springs make the front stiffer and i would liek to know if this is a benefit or if i should keep the Eibachs with the higher rate on the rear?
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Old 05-31-2006, 03:53 PM   #2 (permalink)
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i would like to get some info on this too.
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Old 06-01-2006, 03:50 PM   #3 (permalink)
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I'll start with the difference.

"Progressive" and "linear" refer to the spring rates throughout the compression of the spring.

A progressive spring will have a certain rate at the first few mm of its travel, which changes as the spring compresses more and more. That change will usually be stiffer. A linear spring's rate is constant from the first mm of movement to full compression.


Don't quote me on this, but from what I understand progressive springs are more suited for street use whereas linear ones are better on the circuit. The progressive rate spring gives good initial bump absorption, especially at low speeds where the compression is minimal. The more you compress the spring, the firmer it gets. As you corner hard and pass that initial compression rate it firms up and you get the reduced bodyroll and weight shift from a stiff spring.

However, a linear spring makes the car's weight shifting more consistent as the rate at which the spring compresses doesn't change. Since its stiff from the get-go, the car should get a little less bodyroll and be more responsive as you start turning than a progressive spring with the same maximum spring rate.
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Understeer is when you hit the tree with the front wheel.
Oversteer is when you hit it with the back.
Horsepower is how hard you hit the tree...
Torque is how far you drag it...
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Old 06-01-2006, 04:24 PM   #4 (permalink)
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...sounds pretty legit to me...
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Old 06-01-2006, 06:24 PM   #5 (permalink)
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What's your opinion on the stiffness, should it be kept as stock meaning the rear is stiffer than the front or should it be made to have the front stiffer. Another thing i came across while reading the "Springs" section in the suspension threads is that when installing aftermarket springs the difference in spring rates changes the "roll stiffness" to the front or the rear? Go to the page if you don't know what i'm talking about, the bottom where the springs show a pic and you have some info on them, one of the specs says "Roll stiffness transfer" and some % and either front or rear. I know it may be a bit complicated but i tried to explain myself as well as i could. Thanks for any help in advance.
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Old 06-01-2006, 07:33 PM   #6 (permalink)
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If you find the car too understeery (especially if you've already got swaybars) then you'd want to increase the rear stiffness more than the front. If you're aiming for a drag or V-Max setup then you might want to keep it the same or go softer in the rear to promote understeer.

For me, it depends on what your aims are.

Note that it will also be coupled up with your dampers. If you go aftermarket they'll have different bound and rebound settings, which once again affects the way the car's F/R roll stiffness behaves since stiffer bound means your suspension doesn't want to compress as quickly.

So there's another variable to consider when making a spring choice.


This is a big reason why I've decided to not be my own suspension engineer (even though I have access to a suspension mechanic that sets up clubsport / state championship race cars).

I have Koni dampers but I've decided to go Tein Flex instead of trying to find a set of springs to suit. I was going to do it for a while, to be "different" while finding a good choice, but in the end I realise it would cost a shitload and I might end up something that's only just as good as coilovers.

Spring rates in the Flex are are the same F/R (which means the spring roll stiffness goes to the front) but I can then use the adjustable dampers to fine tune the suspension's net roll stiffness. If worst comes to worst I'll source a set of softer front springs to try bringing the balance closer to OEM.
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Understeer is when you hit the tree with the front wheel.
Oversteer is when you hit it with the back.
Horsepower is how hard you hit the tree...
Torque is how far you drag it...
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Old 06-01-2006, 07:39 PM   #7 (permalink)
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OEM most of the stiffness is on the rear? so then with the springs it changes to more the either the front or rear? This is good info very educational for me at least. So it's really not as simple as it seems to choose your springs. It'll be better to then to choose springs with the same rate front and back and fine tune with some adjustable shocks? or a set of coilovers i assume? Thanks alot for your help and enlightment.
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Old 06-01-2006, 08:40 PM   #8 (permalink)
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Quote:
It'll be better to then to choose springs with the same rate front and back and fine tune with some adjustable shocks? or a set of coilovers i assume?
Not necessarily.

Tein has thrown some time and effort into engineering their products, which is why they are so popular. Now, they've designed their Flex kit for the 350Z with 12kg/mm springs front and rear. If you put 12kg springs with the stock shocks, the thing would understeer like a pig before skipping off the road due to the lack of suspension compliance.

The Cusco Zero-2 coilover kit comes with 10kg/mm springs up front, and 7kg/mm springs in the rear. So, they've gone even further and made the back softer instead of the front! The complete opposite to stock.


But, with the engineering work they've done, Tein and Cusco have come up with valving inside their shocks that match the spring rates they've chosen, and the 350Z's balance. You get some adjustability to fine-tune the balance, but it has to be near enough to suited and the range of adjustability will be within the spring rates' tolerances.

I drove cars equipped with either back to back (thanks MR RIZK and mchapman) over a section of roadworks (where they'd cut parts of the tarmac back to the concrete all the way through an S-bend), and the 2 cars at 35mph felt almost identical driving through those massive craters. I was only testing ride, so I have no idea what the 2 cars are like when at the limit, but on spring rates alone they shouldn't ride the same or the way they do if you compare it to the approx. 5.0kg/mm springs in the stock setup.


Now if you buy shocks and springs separately, they'll come with certain valving inside. But, what springs did the shock manufacturer work with when they designed the product? What were the rates? Was the roll stiffness compared to stock modified? Did they use aftermarket swaybars? Were they just stock springs? If you can't ask them, you have to figure it out yourself. Hence why you become your own suspension engineer.

With a kit from a reputable company you know they've spent the time and effort making sure all the parts work harmoneously. That saves you from having to do it. And you'd hope that they, as a big company, know more about suspension than you (some average guy) so they're more likely to come up with a good suspension setup.
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Understeer is when you hit the tree with the front wheel.
Oversteer is when you hit it with the back.
Horsepower is how hard you hit the tree...
Torque is how far you drag it...
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Old 06-02-2006, 12:51 AM   #9 (permalink)
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Sounds great, this is really usefull info the linear and progressive thing should go into the spring FAQ section. Thanks again for everything.
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Old 06-02-2006, 02:02 PM   #10 (permalink)
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I will add it now.
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Understeer is when you hit the tree with the front wheel.
Oversteer is when you hit it with the back.
Horsepower is how hard you hit the tree...
Torque is how far you drag it...
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