Gsedan35

iTrader: (10)

Bilstein front's are linear, not progressive.

Technically the HKS LS+ and RS coilover rear springs are progressive because the utilize a tapered spring design.

H&R coilovers are progressive? I'm not aware of anyone owning them here, let along anyone posting pic's of the setup itself vs reselller pics that show pics of a non Z33 product (though what I saw did have progressive springs, just wasn't a Z setup).

Z04

iTrader: (15)

i added the H&R because they (the product description) lists them as being progressive all around, didn't even look at the picture because they rarely show the actual product for your specific car. and according to nissan performance mag article on the PSS9, they are front and rear progressive (pics are great too)

http://www.nissanperformancemag.com/april06/350z_turbo/

yusoslo

iTrader: (4)

Well I have to say thank you for providing me with the information on the progressive rate coilovers. I am going to research the spring rates and go from there.

Back to prove my point about cutting the springs. Tensile strength nor shear nor any opposing force that the spring can handle will be changed. It will result in inadvertantly changing the spring rate since now there is less material to distribute the force/weight. This would become very obvious when cutting a stock spring in half. I used a string and found out that my coil spring is over 5' of material so removing 1 linear inch would result in removing 1/60th of the material.

I am going to stop here.

To appease everyone I will not be cutting my springs, but I wanted to prove a point.

WalkerT

iTrader: (13)

The thing you are over looking is the spring has (lets say) 6 coils to hold and react to about 1800 lbs of pressure from the front end. Cutting one out and thinking 5 coils will hold 1800 lbs and react the same as 6 does not make sense. You are changing the load on each coil. By increasing the load this will change to rate of compression.

jadaniya

iTrader: (22)

stop being so irritating guys. the op knows what he's doing. he obviously knows alot, and if there were coilovers meeting his needs he'd get them!

WalkerT

iTrader: (13)

How was my comment irritating? He ask for opinions and there it is.

Z1 Performance

iTrader: (564)

plenty of coilovers with progressive springs and the mere existance of progressive or linear means....absolutely NOTHING. It is all about the interaction between the spring, your wheel, your tire and the valving of the damper. There are many coilovers out there which are incredbily comfortable. Going the route you are going might work but its completely wrong, and you risk ruining a perfectly good set of springs for 1/4 inch of height....sounds a bit lame to me

Z1 Performance

iTrader: (564)

Bilstein PSS or PSS9, KW Variant II - just to name 2

https://my350z.com/forum/suspension/319792-want-coilovers-that-pass-the-wife-test.html

yusoslo

iTrader: (4)

Well I started this post with an idea, and I learned a bit. Now that I know there are choices out there I will shop around for some coilovers that fit my needs.

Anyways thanks alot guys for the informative responses. I just become irritated when people post up abscure reponses with no method of backing it.

Thanks again for the info

97supratt

iTrader: (61)

Glad to help.

Fat chick idea was the best though.

track04

iTrader: (3)

k = Gd4/8nD3
this is the formula for finding spring rate.
here is what each letter represents

k = constant, pounds of load per inch of deflection
G = modulus of rigidity of spring material, pounds per square inch
d = wire diameter, inches
n = number of active coils, which is the number of coils subjected to flexure (always less than the total number of coils)
D = mean coil diameter, inches = Outer Diameter - Wire Diameter

G, d, and D will all stay the same when cutting a spring
n will decrease by the amount you cut the spring, so when everything gets placed back in the equation, your spring rate "k" will be greater

97supratt

iTrader: (61)

I just lost my appetite with all this math.

kuah@splparts.com

iTrader: (10)

Cutting the spring will increase the spring rate, the change in rate is inversely proportional to the change in length. From what you are describing it probably won't affect the spring rate too much. Of course that is assuming you do not heat up the spring too much when cutting it.

Keep in mind several interactions with the rest of the suspension -- The shock valving is probably not a big issue if the spring rate is not significantly changed. However you will change the stroke of the shock, so you may hit the bump stop on the shock under bump. The suspension arms may bottom out under bump as well, most notably the front upper arms are known to bottom out against the fender/frame (when suspension travel is reduced without adequately increasing spring rate).

Gsedan35

iTrader: (10)

I don't think his art work helped matters since it gives the illusion that the springs are linear ones. Eibach prokits are progressive springs. I think he ment to suggest he would be cutting a short section out of the upper progressive part. It's doubtfull that it would have a meaningfull impact on spring rate since the number of active coils covering the softer initial spring rate would not change by much. However slight a additional 1/4" front drop would be, what you mention about piston stroke and the bumpstops is spot on, though it's not really possible to compress the oem bumpstops enough to bottom out the suspension arms. Here's a picture of 350Z eibach prokits, the front springs are of course on the right hand side.

Eibach 350Z progressive springs 1”/1”
Spring rates in LBS initial/final front 296/384 initial/final rear 316/421

kuah@splparts.com

iTrader: (10)

On the front suspension, our experience is that the upper arm ball joint will hit the fender/frame before the shock bottoms out. You may recall the big thread on the G35 forum about the SPC arms on G35s lowered with springs...

It is not so common that the suspension arms bottom out before the shock, but if you look at the 350Z/G35 front suspension, the front shock has a lot of effective stroke, due to the moment ratio to the wheel -- very roughly the ratio is almost 2:1, so 4" of travel at the wheel is only 2" at the shock. That makes it alot more likely for the upper arms to bottom out, or for the ball joint to bind, before the shock bottoms out.

Assuming yusolo measures his shock and suspension travel accordingly and ensures that everything will work, then he is not doing anything "ghetto' in cutting his springs. Cutting springs is not universally bad, but some engineering has to be involved.

Armitage

iTrader: (15)

Its biased to the passenger side though!

TimeAttkZ

iTrader: (14)

hahaha theres nothing comfortable about eibach springs... and yes I have eibach springs on my Z so I know it rides like **** from experience. I cant wait to get them off for a new set of coilovers soon!

You want true comfort get some KW varient 3's.

Control 350z

ok as a former employee/designer for ground control i think i should have a better idea on how this works...

1) as for cutting the springs they will increase your spring rate as shown in below (thank you track04)

2) in about 85% of companies that make progressive factory replacement springs (ie: not coilovers) the progressive part of the spring (the top) is generaly used to only hold the car up with factory weight. they are generaly wound tighter and thicker than factory spring. this gives you the lowered stance and the ability to hold the car up.

3) if you dont know how spring rates work here is the basics if you have a spring with a rate of 400lbs it takes 400lbs to compress it 1" 800lbs for 2" and 1200lbs for 3". by cutting one linear inch off of the spring you have reduced the distance of compression so it will add more to your spring rate. you say you like the ride of the eibachs at their current setting. but you have no idea if you will like it with the higher spring rate HIGHER RATE + LOWER CAR = ROUGHER RIDE

4) also progressive springs twist more than linear springs as they are compressed, so by cutting part of the spring it puts more stress on the spring when compressed, wich as you should know causes the structural integrity to lower. wich can cause coil bind and even a coil snap, neither of wich are good for the shocks. and in a case of coil snap you can damage other parts of the suspension and wheels, not to mention the front end of your car slamming into the ground.

i may have forgotten somethings but it is 1am and im kinda tired

Z1 Performance

iTrader: (564)

Eibach (at leas the prokit) happens to be very comfortable - your tire choice/pressure , or perhaps other factors (worn shocks, worn bushings) is what is making your car uncomfortable, not the springs themselves

Chef-J

iTrader: (58)

Thank god that you going right direction!