Springs

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Intro

Aftermarket springs can improve performance, feel, and looks of you 350Z. The stock suspension is designed to accommodate a wide range of drivers but you should tune the suspension to fit your personal taste. A lower car will have a lower center of gravity resulting in less body roll through corners.

Stiffer springs can help plant the car better, but choosing springs that are too stiff will result in undesirable feel and handling. If excessive stiffness is wanted, shock absorbers should be changed along with springs.

It is impossible to recommend the best spring for any application without defining which shock absorber is used. The 10kg/mm spring in most Japanese coilover kits are perfectly suited for the shocks they come with, but coupled with the OEM shocks (that were a 4.9kg spring) the ride and handling would be woeful.

There are two types of spring designs: linear and progressive. This refers to their rates as the spring is compressed.

Linear springs have the same spring rate from the initial compression all the way to full compression. If a linear spring is rated at 6.2kg/mm (and lets say its range of movement is 50mm) then it takes 6.2kg to compress the spring from 0mm-1mm and 6.2kg to move it from 49mm-50mm.

A progressive spring will have a softer rate for its first few mm of travel, which then increases as you increase the load on it. Lets say we have a progressive rate spring with the same range of movement as above. While it may only take 4.4kg to move it from 0mm-1mm, it may need 7.1kg to move it from 49mm-50mm.

A progressive rate spring is clearly a compromise between softness for ride and firmness for handling. As such, it is more suited for the street. The softer initial rate gives it better compliance, especially over a low amplitude bump. But once you start loading up the suspension the firmer it becomes, so your flat-out cornering is improved.

A linear rate spring would be a better choice for the track, where you do not need to compromise handling for anything. Consistency in the spring rate gives you a better feel, since the car's weight shift isn't as variable. Since your springs are at maximum stifness, initial response is quicker as the car won't want to lean onto its outside suspension as much before the spring resists the movement and the car starts to turn.

Below, we have all of the currently available Nissan 350Z performance springs (at least from reputable companies - we do not believe in endorsing cheap eBay crap). There are two sections below: springs with a mild drop (under 1 inch), and springs with a more aggressive drop (springs 1 inch and over).

Use the spring rates and other data as reference, and keep in mind spring rates may be measured differently between manufacturers.

OEM Spring Rates

F: 314
R: 342

Spring	F Drop	R Drop	F Rate	R Rate	Type	Price
B&G	25mm	25mm	---	---	Progressive	---
Eibach	25mm	25mm	---	---	Progressive	$250
Espelir	25mm	25mm	6.9	9.2	Linear	$225
Hotchkis	15mm	19mm	6.1	5.9	Linear	$149
H&R	33mm	25mm	6.9	9.2	---	$292
kg/mm Street	15mm	15mm	4.4-7.1	4.5-7.3	Dual Rate	$309
kg/mm Racing	30mm	30mm	4.5-8.1	4.5-8.6	Dual Rate	---
Nismo	25mm	25mm	10.7	12.3	Linear	$395
Progress Sports	25mm	25mm	---	---	---	$189
RS-R	15mm	15mm	6.2	7.5	Linear	$220/300
Sprint	44mm	44mm	---	---	---	$329
Tanabe GF210	25mm	30mm	6.0	6.7	Linear	$240
Tanabe NF210	30mm	30mm	5.6	6.3	Linear	$240
Tein H-Tech	7mm	4mm	6.4	6.7	Linear	$165
Tein S-Tech	17mm	14mm	6.9	7.2	Linear	$158