Rear suspension redesign in 1981

[nismoluv]

In these days of on going boredom, waiting for parts, and rationing toilet paper, I found myself reading wikipedia. Reading the same articles I always do. I found an interesting portion of the article that I have never heard before.

 

Quote

"One criticism of the early 280ZX was a reduction in spring rates, giving a softer ride and making the car rather difficult to drive hard through corners without transient oversteer, which was a feature of trailing-arm rear suspensions. The release of the turbocharged model in 1981 saw the introduction of a revised rear suspension, which Nissan continued to use in the 1982 and 1983 turbos, as well as the non-turbo from mid-1982 onward."

 

The s30 guys love telling me the rear trailing suspension sucks therefore your car sucks. I have never had a problem with the suspension or the oversteer.

 

Has anyone ever heard about this revised rear suspension in `81? If so, what was the change, and does it improve the geometry?

 

Sorry for the sporadic thoughts and musings, I may have opened the beer fridge a few cuckoos shy of beer thirty.

[260DET]

No worries, we all are wondering about stuff and things. Anyway I thought that the Z31 had revised geometry, maybe Nissan kept quiet about the earlier revision to use it as a selling point for the Z31.

 

At one stage I did a lot of research on semi trailing arm suspension, BMW of course tweaked theirs to perform very well,  the research led to the UK where some pretty drastic mods were made, not to Z's but whatever Brit cars (Fords?) had STA suspension, it was a while ago. Basically they ended up close to a full trailing arm suspension which proved itself in competition. And of course practically eliminated camber change.

 

The Mac strut S30 rear suspension was great in it's day and still is good but it seems hard to tune, snap oversteer anyone?

[JMortensen]

16 hours ago, 260DET said:

The Mac strut S30 rear suspension was great in it's day and still is good but it seems hard to tune, snap oversteer anyone?

What about S30 suspension makes you think it causes snap oversteer? Is it the linear camber curve, or the lack of dynamic toe change?

Compare to STA with its toe out on droop, and you can see why STA has that reputation, especially with older 911s with the weight hanging off the back end...

[bunkhouse]

I always found the S30 suspension to be very predictable. A Sunbeam Tiger was a handful and defines snap oversteer to me.  

[tube80z]

I can't speak directly about the 280ZX suspension in a Z but we once used that setup in a 510 for rear disks and CVs.  It wasn't a bolt in by any stretch of the imagination.  I did a lot of research into trailing arms and it seemed like one of the big problems is the toe and camber curves are reversed.  If the arms are close to flat in side view when the car is running then a lot of this doesn't matter.  Bit if you lower the car and the arms run at any angle pointing up or down then you get a lot of toe and camber change.   Any alignment change (toe or camber) will move the suspension pickup points and that changes a lot of other things.  Add a lot of power and the car squats getting you into these outer extremes.

 

To get around this we made a custom crossmember that had about half the trailing arm angle (similar to what BMW uses) and fixed the pickup points on the crossmember.  All adjustment for camber and toe was on the arms.  This along with mounting the crossmember higher in the car allowed it to operate in the sweet spot and worked really well on this 510.  Previous attempts with the stock suspension included ever stiffer rear springs, which helped as long as the surface wasn't too bumpy.  On my own 510 I tried a Z bar for a while and that really helped with squat and lift.  Here's a Sierra example and  you can see the fab work to reduce the trailing arm angle.

 

 

If I were to do it again I would have used the rules that allowed any axle locating device to create an extra arm that would run behind the diff and connect to the trailing arm to control lateral load.  Then use the outside mount on the cross member and not hook up the inner mount.  You end up with the equivalent of what Subaru uses on many of their cars.   Here's an example below, which is from a thread where Richard is talking about what he's going to do on his Z31.

 

[260DET]

On 4/18/2020 at 9:51 AM, JMortensen said:

What about S30 suspension makes you think it causes snap oversteer? Is it the linear camber curve, or the lack of dynamic toe change?

Compare to STA with its toe out on droop, and you can see why STA has that reputation, especially with older 911s with the weight hanging off the back end...

 

Go to the end of the vid, syncronised oversteer. Probably over exuberance there LOL

 

 

[260DET]

When I was playing with a trailing arm with two lateral links rear suspension design on a basic suspension program, a change in a pick up point by as little as 10 mm  could make a lot of difference. Variables included both the static and dynamic roll centres where a small adjustment may eg send the roll centre moving laterally by quite a bit with just some vertical suspension movement. So you may work out getting the roll centre up to a reasonable static height only to find it going crazy with suspension movement.

 

Fascinating stuff, if you have a program.

[JMortensen]

[good natured ribbing]Yeah, first got got in over his head, second was trying to keep up. BTW I'd post a video of a 280ZX spinning, but I can't find one. Hey! You're one of the 3 people racing a ZX! Do you have a video of a spin I could post? Sorry, had to.  [/good natured ribbing] 

Seriously though, the Z rear suspension doesn't do anything weird as it goes through it's motion. Linear camber, no toe change. I've spun my Z a bunch of times. Not the fault of the suspension kinematics. ZX toes in on bump and out on droop and has lots of toe change and adding torque compresses the suspension as Cary said. 

I know I've said it before but when I was in auto shop in 10th grade the teacher was explaining STA and he actually took us out in the parking lot, got into an automatic ZX, stood on the brake and put it in reverse, gave it some gas, then put it in D, gave it gas, and the back end was hopping up and down like it had hydraulics and you could see the toe change.

Lots of fast race cars with STA. Miata might have overtaken the 911 as "the most wins in racing history" by now just by virtue of sheer numbers, but 911 can't be denied as a successful platform by anyone with 2 brain cells to rub together. "Any suspension will work if you don't let it" is my takeaway.

[260DET]

A bit of a secret, my 280ZX has S15 rear suspension but originally it could not be mounted high enough so that meant a compromise in ride height. With the second version it's been shoved up higher after extensive body surgery/butchery and has had a GK Tech suspension kit fitted, project is still a work in progress. Would not do such a transplant again, the program I mentioned was showing some some good figures for the trailing arm with two lateral links project suspension I played with, a similar suspension was used by BMW. So something like tube80z mentioned would I think be a practical conversion using a computer program.

 

On the S30 the 'problem' may very well be that it doesn't do anything as it goes through it's motion, like gain some toe  ☺️☺️

 

Ah the 911. Fast into a corner using those big brakes so you can't pass up the inside, doesn't matter what happens mid corner because it's going to block you, fast out of the corner because they put the power down like a front engine can't. Hard to beat something with those dynamics.

[tir33d]

So I have been unfortunate enough to be able to break almost all components in the rear. 
my rear end now consists of a independent nine inch, billet axle and stubs with Porsche race cv’s. All hanging in a modified 280zx subframe. Yes I still break stuff.
this day I found the left was separating itself out near the hub. 
We replated the whole lot, on the left, but replaced the right with a arm from a 280z 1979, (told they were identical - and look identical, bar the brake mount)  strengthened as well. When reassembly we had to remanufacture a dog one for the right rear brake. 
Now although these rear arms arm similar.  I am having terrible issues with camber and toe. The right side is positive camber, even with adjustable eccentric bushes I cannot go negative. 
Car is crazy fast, really pushing the limits on standard suspension points, want to try a R33 style rear but it just takes up to much space. 
We are gonna try removing the mounts and add 3 hein joints. 
I could scare you with some of the measurements of my set up

Edited May 24, 2020 by tir33d

[260DET]

The trailing arm with two lateral links I designed was based on modified Z31 suspension, see the bottom pic in tube 80z's post above for a similar suspension type. For your car tir33d a Z31 may be a better starting point. But I still have all my Z31 5 stud suspension plus a new big brake kit doing nothing, the only parts I'd want money for would be the brake kit plus a bit for the new parts that were needed. BUT, IT"S PICK UP ONLY and some of the fabrication was done to suit a R200 long nose diff. Plus it would all need measuring with the data put through a suspension program. that would be essential.

 

Alternatively, tube's info above is on the money if you want to retain the semi trailing arm setup.
 

[tir33d]

So, I guess it worked , I am able to get a bit of camber and a bit of toe equal on both sides. 
Easier to control on throttle oversteer now. 
Here is how I spent my weekend

 

[HowlerMonkey]

Sanford Silverberg won ITS races with a S130.    

 

There are quite a few cars racing in SCCA that run insane spring rates because they listened to the guy who said "any suspension will work..........if you don't let it."      Kind of the opposite of Colin Chapman.

 

Depending on your car, you have to decide which is better.

[tube80z]

There's a better way to do this but what you have will work too.  If you mount the rod ends on the crossmember and then have the brackets on the control arm.  This way you can change alignment but not cause changes to your camber curve or roll center.  The third option is to let the inner end of the trailing arm float (no connection) and use a lateral locator behind the diff. 

 

I'll see if I can dig up some old pics and attach to this thready.

 

Cary

[tir33d]

I use 5kg springs in rear. Very soft and I have quite a bit of droop. 
I have been watching a heap of the videos ole mate did with his carbon 240z.

Now having a go learning carbon.

If all goes to plan I might make a fuel cell to sit right behind rear towers and mount my wing off the cross between the towers. 
Then I have a bucket load of space under there and we may go to a double wishbone style set up, or at least some sort of locator behind diff. 
can’t wait to cut all that metal out. Carbon Skin is 2kg

[260DET]

If you are considering a double wishbone rear just make sure that it can be mounted high enough into the body so the car can be lowered without compramising the roll centres. There is not much room up there because the original suspension did not need it.

[Chris83zxt]

tir33d:  Do you have the larger ducts in your hood because it helps with cooling or for aero?  Or both?

[tir33d]

Trying to get heat out through bonnet rather than under the car. 
roof ended up saving 19kg. 
bonnet is currently fibreglass at 12.5kg - carbon is under 5kg and stiff