my setup, strongly recommended

[SleeperZ]

All this explanation certainly has it's place, and I'm not going to dispute any of it. I know several folks who just mix and match components like this, and I think David's done a good job with it. He says the ride height is unchanged and the ride is more firm - that sounds good to me, and I don't doubt it. It's a frickin' turbo spring! I'd expect it to be stiffer, more torque, more squat to counter.

[Bob_H]

Wow, that exploded. Funny that it is Zero-Tolerance week over at CC.com as well,(that is corner-carvers.com...)

Anywho. With respect to your RC springs, I think I see where your confusion is coming from. Lets take two identical springs, identical rates, but one is longer. You install them on identical struts or shocks. To compress the shorter spring, "A", to the half way point will require less force than to compress spring "B", the longer one, to the half way point. However, when on the car, they will not reach the halfway point at the same time. The longer spring will require more force,(cornering), to reach that halfway point.

The jump is that for a given cornering force,(say 1.0 G), you are imparting twice the force of a static car on your tires/struts,(not accurate, but for illustration only). So the longer spring will compress,(using my 700lb per wheel example), to a point equal to 1400lbs force on the strut. The same for the shorter spring. The only difference is where they end up. The longer spring ends up 10mm,(or in my example, 1 inch), higher. Which you might interpret as better cornering because the outside is not leaning as far on the strut. But by the same token, the inside is 10mm higher. Net effect is still the same lean in a corner, the same force, the same everything except height and Center of gravity,(won't go into roll centers, etc..).

So yes, it imparts more "force" for a given compression, but the car is unable to see how far it is compressed and that is a totally independent variable. It only knows xxx amount of lbs force.

So calling it a stiffer spring,(your words, not mine), is incorrect. It is only a stiffer assembly. That's it. It makes no difference on handling, taking bumps, nothing.

-Bob

I can't spell to save my life...I won't admit to how many times I had to re-edit this post, to turn heigher to higher or as to a....I suck.

[Pop N Wood]

It's called Hooke's law. Here are some cartoons

 

http://www.sciencejoywagon.com/physicszone/lesson/02forces/hookeslaw.htm

 

This one is interactive and shows how the spring goes "nonlinear" if you stretch or compress it too much

 

http://webphysics.davidson.edu/Applets/animator4/demo_hook.html

 

Now what this doesn't say is what happens to the spring constant if the spring is shortened or lengthened. I have always been told (but have no idea if it is true) that cutting a coil or two off a spring to lower a car will increase the spring constant K. This is what Mudge said also. If this is true, than wouldn't it also be true that the longer, uncut spring actually has a lower spring constant? So if the turbo sping was wound out of exactly the same material than it should be softer? My guess is the turbo spring uses different material (thicker, different alloy or more/less turns per inch).

[Mudge]

The spring acts like a torsion bar, so taking off a coil actually increases the rate, since there will now be increased resistance for the spring to squat down. It wont be a big difference unless your cutting off multiple coils, but still it would end up being too soft IMO to keep a car from bottoming out and riding the bump stops if you removed say, 2 coils in a 9/10 coil spring.

[Mikelly]

Well I didn't want David or anyone to think I was hammering him specifically... I was young once and believed everything supposed experts told me... Boy I wish I had had this board and THESE experts to help guide my decisions... Point I was making here, and to Davids expense (Sorry Dave, Seriously) is that there are sooooo many good resources on this board to get guidance from for everything performance related to the Zcar.

 

Peace!

Mike

[David K]

No harm taken. While i may be simply misunderstanding what you fellows are 'splainin to me, i think we are on the same track, just me trying to explain without the knowledge of some of the elders here. There has been some great info in this thread and i appreiciate it.

[Bob_H]

Just as long as we are on the same page. I take the following from your posts:

So thus, the more compressed the spring is, makes it stiffer and allows the car to recover faster from whatever you throw at it.

So yes, and no. The ride height it not higher, yes the spring is stiffer.

You realize both these comments are incorrect. The car will not recover faster, will not have the same ride height and the spring is not stiffer. That is the basis for contention. I think you understand spring constant and such,(or do now), but my important point is it makes NO difference in the handling in a positive way. It is negative because it raises the ride height. But that is a negligible effect.

[Oltmann]

Originally posted by SleeperZ:

All this explanation certainly has it's place, and I'm not going to dispute any of it. I know several folks who just mix and match components like this, and I think David's done a good job with it. He says the ride height is unchanged and the ride is more firm - that sounds good to me, and I don't doubt it. It's a frickin' turbo spring! I'd expect it to be stiffer, more torque, more squat to counter.

If the free length of the spring is in fact longer, and the spring is stiffer, then it follows that the ride height must be higher.

[Mikelly]

And, due to the fact that it is a progressive rate spring, your feeling of it being stiffer is just the fact that your compressing it down has pushed it past the softer side of the progression, and the car is riding on the stiffer setting. The other comment earlier about shock valving being effected negatively is also correct. I think you will experience strut failure MUCH sooner...

 

Mike

[David K]

I think you will experience strut failure MUCH sooner...

 

Mike[/QB]

No it will not. the shock is for turbo zx as well as n/a.

[johnc]

David,

 

I don't know the rear suspension of the ZX very well (swing axle right?) Is the installed height of the spring constrained by the maximum extended length of the shocks? If so, is it by the 1/2" difference you mention in your previous posts?

 

[Edit: Ooops. I meant semi-trailing arm. Swing axles were on old Triumphs and Bugs)

[Bob_H]

My turn.

No, no, no, no, NO!

Ok, I feel better. (to noone in particular)

Alright, first, experiencing shock failure sooner. Again, no.

While the installed pressure is higher, the shock still sees the same effective force each time. The only factor to consider is if you are artificially hitting one end of the travel, i.e. smacking off the stop for rebound,(extended).

And Mike, where did the progressive spring come in? I guess I missed that one. I have always been talking about a linear spring as I thought others were....

BTW, Semi trailing arm for the ZX, sort of similar to the E30 BMW's and the M coupe/roadster. Just not as refined. Also called swing axle.

-Bob

on spelling edit,(see, I suck), some thoughts.

First, with only the rear springs changed to the longer springs, you will see one positive benefit, less squat. In all the comparisions, I have been referencing left to right, i.e. turning.

[260DET]

Hmmm, mass confusion, lets try and settle this.

 

Proposition: if springs are installed pre-loaded ie compressed on the strut removed from the car, then the effective spring rate is increased.

 

Because, actual spring rate is determined by starting with the sring at its free length and then compressing it. The amount of load that a free length spring will bear before the spring compresses by a certain amount determines its rate. And, the more the spring is compressed the higher the amount of load it will bear.

 

Ride height is determined by spring rate, and, the position of the spring on the strut. The higher up the strut the spring's bottom platform is, the higher the ride height.

 

Of course it would be possible to use a spring of such a high rate that it would not compress at all under static load. In that case, any further increase in spring rate would not increase ride height.

 

Now, is all the above correct, or...........?

[Mudge]

Originally posted by Mikelly:

is that there are sooooo many good resources on this board to get guidance from for everything performance related to the Zcar.

So true, there can be some things spread that aren't true but will believed, but for the watchfull eye if you spend some time there is EXCELLENT info on boards and member sites, on engine buildups, problem areas, suspension you name it, in that regard the internet ROCKS.

 

To think that almost nobody believed the home computer would go anywhere, eh...

[TimZ]

Originally posted by 260DET:

Proposition: if springs are installed pre-loaded ie compressed on the strut removed from the car, then the effective spring rate is increased.

 

No, it isn't. Because the spring is compressed farther, it exerts more FORCE on the spring perch. Force is RELATED to spring rate AND the amount the spring was compressed. Again, force is related to spring rate, but not the same as.

 

Further (and this is about the tenth time this has been covered), because the longer than stock spring will be supporting the same weight as before, it will act exactly the same as the stock spring (remember that the spring rates are the same - only the length is different), except the ride height will be higher, and the shock will reach the end of its travel sooner.

 

Because, actual spring rate is determined by starting with the sring at its free length and then compressing it. The amount of load that a free length spring will bear before the spring compresses by a certain amount determines its rate. And, the more the spring is compressed the higher the amount of load it will bear.

 

That's almost right. A free length spring (by definition) does not support any load. If it did (by definition) it would be compressed. The spring rate for a linear spring is determined by measuring the amount of force it exerts at a given amount of compression. The rate is the force divided by the amount of compression.

 

You just have to remember that the force exerted is not interchangeable with spring rate.

 

Ride height is determined by spring rate, and, the position of the spring on the strut. The higher up the strut the spring's bottom platform is, the higher the ride height.

 

Ride height is determined by the spring rate, it's position on the strut (assuming you have a strut), the spring length, and the amount of load supported by the strut.

[Mikelly]

Actually all the factory springs were of the progressibve rate type... IE They go from their softest, most compliant setting at sag, through their stiffest, most compressed setting... In other words, there are several numbers associated with progressive spring rates, vs. a straight rate spring... My point Bob H. was that by compressing a longer progressive rate spring, don't you compromise the rate of original operation of the spring, stuffing it and its strut cartridge into a more compressed area, doing a couple of things like blowing through the rate of the spring compliance and also reducing (Negatively of course) the amount of stroke on the strut, and causing the strut to operate in a smaller range of action, which will impact valving significantly. If a strut is optimized for proper operation in a 4 inch stroke, and then is compressed in such a manor that David describes to only be used through the last 3/4 of the travel, then the stroke, valving, and general operation of the cylinder is changed, possibly causing valve seal failure, and certainly causind excessive heat build up due to the inability to disipate heat through that extra 1/4 of the travel... I'd bet on potential premature strut failure.

 

One thing that would have been nice is to measure the ride height of the car with factory springs/ struts and then measure with the Turbo parts installed... Right now we are dealing with some unknowns...

Mike

[Guest Anonymous]

Unknown??? Anybody that fools with a hybrid Z ventures into the realm of unknowns .You can't argue with success and a fellow pleased with his results . David (LOL) quit all this agitating with these renagades before this thread reaches the 200 post mark

[Bob_H]

Uhh, I don't believe it. Point me to figures showing stock springs were ever progressive. If you can, I admit I was wrong. I Understand what you were saying if indeed we were dealing with a progressive spring. However, I am fairly sure that is most certainly not the case.

If a strut is optimized for proper operation in a 4 inch stroke, and then is compressed in such a manor that David describes to only be used through the last 3/4 of the travel, then the stroke, valving, and general operation of the cylinder is changed,

No, no no. The valving does not change. It is valved for one rate from end to end unless you get some super fancy custom changing valve thing which most certainly won't be $50. (no, I am not talking about adjustable shocks)

First, looking at David's car, the neutral point has moved 10mm higher, or about 3/4 of an inch. For a 5-6 inch stroke, that is very minor. In my view, the more critical point is compression, not extension. Hitting a bump is more likely to cause damage than extending the shock to the end of its travel upon jumping. So lowering it has a more negative effect on shocks,(meaning hitting the stops). The shock will behave the same in the last 3/4 of a stroke as it did in the middle 2 inches. The only thing possibly changed is the stroke,(meaning where it moves, not how far). And that has little effect if any on the operation of the shock. Its ability to disapate heat based is not affected by the location of the stroke, unless you move everything to the last 1/8 of a stroke. Which we are not doing.

You claim stroke, valving and general operation change. None of those will change. The location of the stroke will change, but that's it, and 10mm at that. And until you hit the end of travel,(again, only an issue in extension, and minor at that), nothing changes.

[Mikelly]

I'll have to dig it up in an old Zcar Magazine article on suspensions, but I'm pretty sure the factory springs weren't a constant rate... Also I think we are talking the same issue... If he has crammed a longer spring into the shorter tube area, you're right in the sense that it won't "TOP" out ever, causing the reverse issue of what I explained. However, when I went to a class at Mid Ohio in 1995 with the Koni Reps, they pretty much explained to me what I've relayed above... Of course it was geared towards cars ON a race course, being driven much harder than typical street use...

 

Mike

[Guest DRK]

Formula for calculating the spring rate:

 

rate = ( wireDia^4 * 1470000 ) / ( coilDia^3 * numCoils )

 

Units are in lbf/in

 

Danny