I have read that cutting springs to lower a car is ghetto and other negative terms. I have read that it will make your car bouncey and handle like s***. I must be missing something! I have been taught that handling is based on the cars geometry. Most aftermarket springs are generally shorter and have a higher spring rate. If you cut a stock spring it will also be shorter and have a higher spring rate. Once mounted in the car the geometry of the cut stock spring could be made equal to any aftermaket spring. With the same c/c plates, struts and bump steer adjustments I don't believe the cut spring could be distinquished from an aftermarket linear rate spring. I have found several tricks for regaining the proper geometry without all the aftermarket expense. I beleive in spending the money where it benefits. If you can afford coilovers they give more flexibilty in adjustment and are superior. If my choice was between aftermarket springs and non adjustable struts and cutting my spings and getting adjustable struts I would take the adjustables. It's all about the money and I'm sure the spring manufactures love every minute of it. Am I wrong?

Does the 240sx have a flat end coil (the part that sits on the perch). If not, you can cut your springs w/ good results. It has to be done right though. There are a few books out there on suspension geometry and chassis design that go into detail on how to properly cut your springs. The problem w/ cutting springs is that it's usually done wrong and the result is an unbalanced, uneven car. But with the right resources, it can be better than buying an aftermarket spring.

Books to help:

"How to make your car handle" by Fred Phun

"Chassis Engineering" by Herb Adams

You don't need to be an engineer.

I appreciate the response and the equation. Looking at your equation it would seem that in a linear rate spring all of the variables would remain the same except for number of coils. Removing one coil from a spring with 10 coils would give a 20% spring rate increase. If you cut it in half it would double. To lower a 240 1.5 inches we are not talking multiple coils thus putting the spring rate into the same relm as many aftermarket springs. I have talked with autoxers that understand thier suspension better than most people who believe that they could acheive the same results from cut springs They won't do it because of the bad rap. The biggest handling issues I have found from lowering vehicles comes from the change of the lower control arm pivot point and the rack being lower and the tie rod angle changing. Cut springs or aftermarket this problem exists. C/C plates will help with camber and caster but they do nothing to solve the changed pivot points. I admit I don't have decades of experience but i have been beyond adding new springs and struts. I have fabed many components including control arms, STBs, bump steer kits, sway bars and sub frame connectors. I have solved the pivot point issues for my early Zs in my shop . I haven't even looked at my 240 sx yet but I bet many of the same techniques will apply. You may have more knowledge in this area than I do so let me have it. At least it's not the same old question of what springs to use. Helping everyone to understand suspension geometry is a good thing.

If you want equations, look to hooke's law. Here is a good link w/ animation/explanation:http://www.sciencejoywagon.com...w.htm

Here's an easy way to say it...say you have a spring with a linear rate spring rate of 300Lbs/In. It takes 300 Pounds to compress the spring one Inch. Now say this spring has 10 coils and is 10" long. Each individual coil takes 3000Lbs to compress them 1". But when you take all 10 coils and put them together it only takes 1/10th that much effort to move it 1". So lets slice 1" off the coil. You now only have 9 coils, at 3000Lbs/inch a peice, and your total spring rate is now 333Lbs/In. About a 10% increase in spring rate.

Check this out too:http://www.efunda.com/DesignSt...k.cfm

Get it?:)

Lost_To_A_K-Car wrote:That depends on the original rate of the spring, and the rate of the aftermarket springs. I don't know the rates for either off the top of my head, do you?

The stock S13 spring rates are around 112 lbs/in IIRC. Most aftermarket lowering springs are anywhere from 1.5-2x that -- something you can't get from cutting coils.

The bottom line is that while cutting coils does give you a lower, stiffer spring, the stiffness increase is not enough to prevent the car from bottoming out given the amount of lowering.

Asad

How many coils are in the stock springs and how many (if any) dead coils are there? How do the springs mount on the perch? Flat or not?

Dori Dori wrote:How many coils are in the stock springs and how many (if any) dead coils are there? How do the springs mount on the perch? Flat or not?

I want to say there are 5 or 6 coils in the stock front 240sx springs. Not sure about the rear.

The ends of the springs are not ground flat.

Asad

I want to thank all of you for replying. It's great to be able to do the math and know exactly what to expect. In the end I believe Asad is correct . I looked my car over today and you can't reach an appropriate height and spring rate. You would have to cut the stock 240sx spring in half to match the aftermarket rates. At an appropriate height the springs would be at about 140 lbs/in. In the early z's, aftermarket spring rates are only 15% - 40% higher than stock. You can easliy acheive these numbers by cutting their springs. The 240's aftermarket springs being at 100% increase makes it very difficult to match.

Ok, now that I'm home I can add some more info.

Here's the info from the FSM (front springs only, cuz I'm too lazy to type out the rear info):

Non-HICAS Hatchback/CoupeFront:Wire diameter mm (in) : 13.4 (0.528)Coil OD mm (in): 170.4 (6.70)Free length mm (in): 350 (13.78)Spring constant N/mm (kg/mm, lb/in): 17.7 (1.8, 101)

Convertible is the same except the free length is 356mm (14.02")

HICAS HatchbackWire diameter mm (in) : 13.3 (0.524)Coil OD mm (in): 170.3 (6.70)Free length mm (in): 336 (13.23)Spring constant N/mm (kg/mm, lb/in): 19.6 (2.0, 112)

In addition, I've attached a pic I took a while back of my front Suspension Techniques lowering spring. I would say it has 3 active coils when installed? I don't remember what my stock springs looked like though.

Anyway, hope that helps.

Asad

And to ad my $.02.....

I bought my 240 and it has cut springs. I have driven lots of different cars in autocrosses (mustangs, camaros, supras, 240's, cavaliers, accords, civics, etc) and I must say that the ride on these cut springs is 100 times worse than any of the other cars I have ever driven in my life. It is like driving a boat.

Where you located in Austin? Im in Austin too... whats your name? Hit up the TRS meets any? Feel free to IM me on AIM...

Zalanbud is my AIM name.

Nismo Freak you can reach me at [email protected] .

I did the same thing as cutting the springs on the front of my 240. I just installed some of those spring clamps, which eliminates one coil. This lowered it a little, barely noticeable. It did make the front stiffer, however, since my shocks were going out, it causes them to be drastically underdamped and the ride was much worse. So I took the clamps off, but the damage to the shocks had already been done. I didn't think it would be that bad, but it was. I would assume that most people who say cut springs are bad had a similar experience. I have no doubt that if I had adj. shocks that could become stiffer then the stock shocks, that I would have been able to get back to the original damping/spring ratio. In general I say that it is doable, and I have seen people use it with good results. I don't plan on playing with my springs till I get new shocks, then we'll have to see what happens.

To bring up an old post....I recently cut and heated my factory springs the "right way" and overall I'm pretty impressed. They feel identical to my 91 with the Eibach pro-kit. I haven't done the math yet on the new coil spring rate, but you can feel the difference. I don't feel that they are bouncy at all, but definitely stiffer. I have yet to take it to the autocross, so maybe that will be the ultimatum(sp?), but the negative camber helps the cornering pulling into Suburbia. FYI: I cut 1 coil in front, 1.5 in the rear, and it lowered the car exactly 1 1/2 inches all around with a very level, very perfect stance. I'm still on factory struts (they'll probably last a week!) and you will want to trim the front bumpstops about 1/2 to 3/4", the rears are fine. Keep in mind you can buy a nice set of performance springs for the cost of what a shop would charge to do this, but if you've got acetylene...

Nice, make sure you report back when you do autocross