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.:shrug:

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. :shrug:

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. :o

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

[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

[TomL]

Paul -
I realize you can move the center of travel a bit by adjusting strut tube length and the size of the spacer (or not using one) under the insert. I just don't see how that is influenced in any way by the length of springs you use, which was the original question. Or was I reading to much into your response - that centering the shock is a good thing in general (and you weren't addressing the spring length question?)

[pballance]

TomL and Tom, my last response about centering the shock was more for TomL than TomD. Too many Toms around here I guess we just need some "Harry's". :) I'm not going looking for "Richard's" :)

TomL, I think maybe I wasn't clear enough and maybe you read a little too much into it. Get the shock where you need it, then figure out the length of the spring from that based on your artificial (mocked up assembly) ride height. If you have a delta that might allow you to use springs of 2 length's, let's say 9" or 10" and still get ride height and adjustability, then go with the shorter i.e. lighter of the 2 springs.

TomD, I have only seen different length springs on struts that used the OEM perches for the lower mounting point of the springs. Some tubes had been sectioned, others not. If I were in your shoes, and could use 4 springs of equal length and get the car set, that is what I would do. Otherwise SHUT UP AND DRIVE! didn't we have that conversation? :D:D

[kthomas]

If I were in your shoes, and could use 4 springs of equal length and get the car set, that is what I would do. Otherwise SHUT UP AND DRIVE! didn't we have that conversation? :D:D

That.

The natural frequency of the suspension springs for the rates and dimensions commonly used on 240Z's is inconsequential. Now you want to talk about spring harmonics when it comes to valve springs on and L24 and we have something worth discussing. We always used 10" free length springs on cars I prepped because I didn't have to worry about stack up for any reasonable rates, and it put the spring perches in convenient places relative to the strut tube to not cause any issues or clearance problems.

We won a ton of races back in the day with rates under 250 on both ends. Big springs, remember, are going to require more consistency and precision on the part of the driver, and may not be as much fun to drive, or drive well, depending on how regular your track days are.

[Tom Donnelly]

We won a ton of races back in the day with rates under 250 on both ends. Big springs, remember, are going to require more consistency and precision on the part of the driver, and may not be as much fun to drive, or drive well, depending on how regular your track days are.

Keith,

Glad you're still around! My plan was lower spring rates and increase them as my track time, consistency and precision goes up. The lower spring rates are more forgiving right? And not necessarilly slower. I need to run newer than 8 year old tires too.

Tom

[kthomas]

Keith,

Glad you're still around! My plan was lower spring rates and increase them as my track time, consistency and precision goes up. The lower spring rates are more forgiving right? And not necessarilly slower. I need to run newer than 8 year old tires too.

Tom

That, gentlemen, is a man who don't let ego get in the way of good decision making.

Higher rates are ultimately faster on paper because the aid to roll control gives a better contact patch provided the shocks are up to the task, however, you've heard me say that a softer car is faster sooner- meaning if you aren't driving a lot (twice a month+ may be enough for an ITS driver to be on his game) you may be faster in a softer car, and faster earlier in each track weekend because you acclimate sooner. Now if the car is wallowing all over the place because the shocks don't work then softer won't help, but you know what I mean.

Chet and I ran front row ITS times at Roebling one weekend in a $300 240Z with a 150k bone stock motor and some old race pads and tires with the old Bob Sharp street Koni package on it- about 115 lb/in springs up front and about 140 in the rear. Some of the most fun I ever had on a track ('course a lot of that was because we were kicking major Porsche butts with a $300 car, but I digress) because it was balanced and the shocks matched the springs well. Blast to drive, went where you pointed it, and recovered predictably when you got out of whack. Wasn't as fast as our ITS car mind you (which I hear ran 117's at Roebling a couple years ago, Holy $h1t!), but I'd venture to guess that most of an ITS field would be faster in that $300 car for a Saturday qualifying than their own race car.:eclipsee_steering:

[Ron Earp]

Wasn't as fast as our ITS car mind you (which I hear ran 117's at Roebling a couple years ago, Holy !),

Is that correct? If so I think that would have the ITS record. The fastest Z that I've seen down there in the last few years at the SARRC weekends has been John Williams' car in the low 1:20.xx. As far as I know Jeff or I haven't missed a SARRC weekend down there.

[kthomas]

That was according to the current owner, Bobby Bitterman in AL. The car now races vintage, but is still in IT trim, tires, and the Sunbelt IT motor that was sold with the car. Not sure what if anything might have been out of IT spec other than the RR shocks. I could be wrong, but I'm pretty sure he told me he turned laps in the 1:17's. It was captured by the data acquisition system on board so perhaps there's proof.

No doubt in my mind that car would be faster than John Williams. 1:17's? I dunno.

[Tom Donnelly]

[quote=kthomas;294658]Not sure what if anything might have been out of IT spec other than the RR shocks./quote]

Keith and Ron,

I know Keith said same tires but slicks are allowed in vintage. He probably ran slicks. Which would help close the gap between ITS and EP times. That would be close to the same setup in Grayson's old car I think. Then 1:17's would be real doable. Don Ahrens ran a 1:17 last year in EP at Roebling in a 240z.

Tom

[Tom Donnelly]

Hey, how come my quote stuff didn't work?

[specialtyautomo]

Actually it was a 118 and small change. The car was on dot's and the only thing not ITS legal is the rr shocks. Great weather and good drafting partners a (gto and a 914-6). Three laps were in the 118s. There is alot of set up difference between Johns car and mine. Most of the lap time came from turn one and two. Enough corner speed that I stayed in 4th gear from the front straight untill turn 4. I have learned that Z cars are very alignment sensitive.
Bobby Bitterman

[Charles Perry]

Ok Bobby, you know someone was going to ask! What did you do alignment wise to get through 1 and 2 so well??? Z car guys want to know!

[specialtyautomo]

The easiest way to put it is that Keith took full advantage of the rules when it came to strut housings. I am lucky enough to have two sets (one set for each car). Most, if not all Z cars have bent strut housings to get the proper camber. Having had a set of those in the past and compairing them to what I now have thats not the way. My experience has been that Z cars want all the camber that you can get and then some. 3-4 degrees isnt enough, closer to 5 will get you in the ball park. The only difference in the car from when purchased is the alingment and the driver. I am nowhere near the driver Chet is, I would bet his time would be even faster. I can say that that alingment does not work as good for RA though. It works at Barbers and Roebling.
Bobby Bitterman

[gira]

Good Day folks,
My two cents on this topic real quick. First off, a coil spring is only considered 36% unsprung weight, so buying an IT spring with this as the main criteria might not be that great. Some people think a longer spring produces more reliable results. I like trying to use the same size springs so that I'll have more choices to change my chassis setup. Once the front tubes are sectioned, changing the shock body length and shimming up and down inside the tube could only change your droop travel since the top of the strut and the bump stop will not change location. Once you get the components in the right location at your normal ride hide, you shouldn't have to change it that much. We use 10's and 12's I believe and incorporate a 2" space sometimes.
Hope this helps.

greg ira

[dspillrat]

Is that correct? If so I think that would have the ITS record. The fastest Z that I've seen down there in the last few years at the SARRC weekends has been John Williams' car in the low 1:20.xx. As far as I know Jeff or I haven't missed a SARRC weekend down there.

Jeff/Ron......This series one 240z "Keith is refering to" ....Blue/Blue car wasn't super fast...in a straight line, but handled quite well..I was privileged to be a passenger in with Chet driving that weekend back in 1999/2000 maybe.... I remember well cause Chet done blowed my engine up that weekend telling me to go faster :eek:.......Damn V-8...
Many moons ago......

Ready to try some extreme camber at the SIC........Hmmm...

David Spillman.......