More 240z Suspension Questions

[Tom Donnelly]

Ok, I've gone over the new car's suspension and I've found something I don't really understand. My old car had 8" hyperco hypercoil springs in the front and 8" carrera's in the rear. Why? I dunno. That's just how I bought it. 350lbs front, 325 rear.

New car, same manufacturer but different rates. Unknown front and 300 rear. And, the new car has 12" hyperco's in the front and 10" carrara's in the rear. I just ran it at driver's school and the last 2 events as it was, but now its time to get to a known baseline and start from there.

I'm going to purchase a few sets of springs to test with, starting with katman's series of springs and a couple of David Spillman's as well. Maybe 325/275, 350/275, 350/285, 400/300 and 400/350.

Here's the questions. Is there an advantage to longer coils? The fronts are almost out of room on the adjusters (but the car is low enough) and the rears are similar. Do longer coils have better progession? Or do they bind easier due to more coils? I have found that the 12" coils weight about 2 1/2 pounds more than the 8". So there is at least a weight savings on the smaller springs.

I was going to go with possibly a series of 10" or 8" with the front and rears being the same height. But I'd like to know the trade offs in each direction if anyone knows.

Another question is.. Hyperco or Eibach or Carrera or Landrum? Any feedback on manufacturer?

The last two sessions at Road Atlanta the car was real twitchy in the esses and even in turn six, where I spun. And I've never spun in six. The setup was an unknown spring rate in front and 300 lbs in the rear, with 8 year old tires. (which may have been the problem, besides rusty driving)

Thanks in advance,

Tom

Oh, and the car is a 1970 240z, Bilstien shocks, speedway front bar and no rear bar.

[pballance]

What matters Tom is you need to set the shock in the center of it's range of travel. You will need to find the specs on the shocks, then assemble everything w/o the shocks in place and make sure you have enough travel, both compression and rebound, with your car set at the correct ride height. You may find that changing length of the spring will allow you to center the shock while obtaining the correct ride height.

A lot of work, but worth it to get the suspension working right. Go read the "strut" thread at hybridz when you have time. Lot's of good info.

[Tom Donnelly]

Paul,

I didn't think about shock travel, that's a good point. Any feedback on manufacturer?

By the way, which strut thread? There are a bunch.

Tom

[pballance]

Try this one Tom,
http://forums.hybridz.org/showthread.php?t=138601

I am using Eibach but have used hypercoil and carerra. I would think that consistent rate would be more important than brand. Then it comes down to the weight of the spring.

Good luck!

[Tom Donnelly]

Paul,

Thanks.

Tom

[Tom Donnelly]

What about spring length? Does it make a difference? Say a 300lb 12" spring versus a 300lb 8" spring. One is lighter than the other. And longer. What about travel, binding etc. If it's just length, then why doesn't everybody run lighter 8" instead of 12". It seems like travel would be greater with the 12's but there are more coils than the 8's so is it different. And I was just wondering about personel experience with manufacturers. Landrum is right downtown here in Atlanta, (sort of, they're in Conley). They're all priced about the same. Just different colors as far as I can tell.

Tom

[Tom Donnelly]

Anybody know?

[joeg]

How much travel you need?

In a race car with adjustable coil-overs (and the weights we are dealing with)' it is unlikely you need a great deal of travel (free-length).

As to brands, when you are dealing with quality springs, the only difference is the powder coating color. You can use Hypercos, eibachs, Gc, carrera, etc. mix and match.

[Mike Mackaman]

Use the spring that gives you an unsprung weight you like. I personally like zero, but they don't make that spring in the rate I want so I run the shortest that will work.

Mike

[Tom Donnelly]

Use the spring that gives you an unsprung weight you like. I personally like zero, but they don't make that spring in the rate I want so I run the shortest that will work.

Mike

Bingo! That's what I was thinking but I guess I wasn't saying it right. Although, is a spring unsprung weight? But lighter is better, correct?

[joeg]

I said the same thing, Tom.

"Free length" is the length of the spring--shorter is lighter; it's just a matter of mass.

[Tom Donnelly]

I said the same thing, Tom.

"Free length" is the length of the spring--shorter is lighter; it's just a matter of mass.

Ok, cool. I didn't catch that. Sometimes you just gotta spell it out for me.

Thanks to all three of you.

Oh, and Robinson Racing has a spring tester. So I guess I'll be heading up there soon.

[pballance]

Ok Tom, I checked my notes and you should shoot for shock travel, for Bilstein, 2 3/4" - 3" bump and 2 1/2"-2 3/4" rebound. So roughly 5 1/2" total travel.

I did assemble my suspension and check travel and wound up getting 10" springs. That sounds long but I now have plenty of adjustment and when I re did the coilovers I changed the upper hat and put in camber plates. Needed the longer springs to make it work out right.

Of course, if we are at the point of weighing springs for their "unsprung" weight then I assume we have a 10/10ths build and that the driver will notice the difference.

In my car, I know that isn't the case. The driver is doing good to show up.

[Tom Donnelly]

Thanks Paul.

I finally scraped the rust off in enough places and found the weight markings on the springs.

375 front (hyperco) 300 rear (carrera).

I was thinking of testing with 350f/275r and 375f/275r and then 375f/300r like it is now. Keith ran 400/350 at one point but that was with RR shocks. He won the ARRC with Bilstein's and 350/285. I dunno who makes 285 lb springs, maybe Carrera did at one point.

Thanks again to all who posted.

Tom

[TomL]

Paul-

Sorry, but I don't understand your point about choosing your spring length to "center your shock travel". Once you choose your shock brand and length, and decide on your ride height, the shock "center" is going to be wherever it ends up, based on the shock length and the dimensions of your specific car. Seems to me that no matter what length spring you use, the shock rod will end up in the exactly the same place relative to the shock body, unless you change the ride height. The only thing that will change is how high the lower spring mount sits. Or am I missing something? I realize you want to not end up with the shock near either end of its travel (particularly compression), but I don't see how spring length enters into the equation, except as it may limit your ability to set the car at the desired ride height.

[chuck baader]

Reference: Carol Smith....changing spring length changes the natural frequency of the spring. If you get the natural frequencies off front to rear, strange things happen. Chuck

[pballance]

Hey Tom,

If you section the strut tube correctly on the Z you can move the shock up and down in the tube using different length spacers in the bottom of the tube. Of course that assumes you are using a shock that is shorter than OEM that gives you the dampening you want. You have about 1-1.5" to play with. That way you can center the shock while getting the ride height you need. At least it worked that way for me.

In the back, you have even more to play with since you leave the tubes a little longer when sectioning.

Paul

[Tom Donnelly]

Reference: Carol Smith....changing spring length changes the natural frequency of the spring. If you get the natural frequencies off front to rear, strange things happen. Chuck

So a 12" spring would act differently than an 8" spring. Right? So how does more or less free travel change things?

And Paul, its not so much that the shocks need adjusted around, I was just thinking of going to either 8, 10 or 12 inch springs all around.
To make it easier to change things without re-scaling the car. But if there is an advantage to longer in front, say, smoother transitioning / less twitchy and shorter in the rear, (why, I dunno), then I shouldn't change the results of prior testing. I know my driving style isn't like the former owner. Larry Stepp liked a stiffer suspension if I remember right. His BMW was stiffer than Chet's. But Chet ran the ARRC in the 240 with 400/350 f/r. So, like I said, I dunno.

[Tom Donnelly]

Of course, maybe I should quit thinking so much and just shut up and drive.

[chuck baader]

Two identically built cars will usually use two different sets of springs and bars. Read Carol Smith's book and he explains the relationships. That is way advanced and over my head...I just changed and lucked out to get the balance very good front to rear. I finally am just driving. Chuck