Semi Trailing Arms

[Richard85ZXT]

I have a first generation Nissan 300ZX with Rear Semi Trailing Arm suspension. While many cars of this time used this type of suspension, especially European and Japanese manufacturers, they appear to be very outdated. I may in the end swap to an alternate suspension entirely, but since I have a couple, and one is a daily driver, is there any hope for the STA? Most of the guys with these cars don't take the time to understand suspensions, and while I am WAY behind many of you I have found myself almost too far ahead of many other enthusiasts and in need of understanding and help on many areas. General thought on these cars is that stiffer springs/dampers, lowering, poly bushings, wider tires and maybe stiffer roll bars is the extent of handling abilities with the STA. While Simply trying to find out the best way to find the CG so I can attain a proper Roll Center most the community was confused as to what I was doing and a couple even said, it doesn't matter where it is, lower CG is better, so just lower the car. One member, who rarely is on posted up this site, thankfully, and I have been reading and learning. While I know I have a lot more to learn, I thought I'd simply try to find out is it worth while to try and adapt a STA rear suspension for occasional track use while maintaining the comfort of a daily driver? I am in an area where the roads are rough so stiffening the entire suspension would be a death sentence, and by being a STA any lowering makes Negative Camber excessive. I am sorry for the long winded post and lack of technical speak, but I am still learning, and started reading a couple of the books in the FAQ section, but until I put it into practical use I feel it'll seem a jumble. Thank you all for taking the time to explain in depth and share your knowledge with those of us still learning, I truly do appreciate it.

 

[GregLocock]

Well, first and foremost lower CG is always a great plan.

Stiffening the suspension works in two ways, first it allows you to run a lower ride height, secondly it prevents any inherent lousiness in the kinematics of your suspension from expressing themselves.

But, your traction out of corners will suffer.

STAs are pretty crummy. Twenty years ago they were generally recognised as being crummy. A /good/ live axle is better than the best STA, except on rough roads.

Opel and Lotus (and others no doubt) added links to their STAs to try and reduce the general crumminess, but typically those lasted less than 5 years before being replaced by proper IRS.







Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Richard85ZXT]

Thanks Greg, sounds like my researching of a swap to an IRS was worth while then. I was only hoping for a car I didn't want to do nearly as much work on there would be a simple solution, but it sounds like there is not.

 

[BrianPetersen]

By "occasional track use", how close to lap-record-setting times are you proposing to run ...

If you are staying below (say) "eight-tenths" as on a normal track day, then it probably doesn't matter too much what sort of suspension you have. There are plenty of cars out there with suspension designs that are currently regarded as sub-optimal, and people still do track days and maybe vintage-race them. So, how much do you want to spend re-working the rear suspension of that car and not necessarily getting it much (if any) better than Nissan did originally?

 

[GregLocock]

I forgot Porsche 928, which when all the shouting is over is an STA, isn't it?


Maybe the first thing to look at is tire wear and temperatures. If the temps are ok across the tread, and they wear evenly, then you could argue that the tire is being presented correctly to the road and that there is not much to be gained kinematically.


Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Tmoose]

BMW 2002/320 -

http://www.lexam.net/peter/carnut/320-rear-suspension-drawing.jpg

http://www.ancientcirclels.com/images/2002/10.14.07/RearSubframe_03.jpg