S13 Suspension with S13 coilovers. . .

[New-to-240z]

So, I'm having the S13's suspension fabb'ed up to my 73' 240Z in a few weeks and I'm looking to purchase a set of coilovers to install on them. I was wondering if anyone here could help me out with a simple question . .

 

Should I ask for a new spring rate and have the shocks re-valved?

 

I ask because most of the setups I see for my car (240Z with SR20DET) are running Illuminas with F225or200/R250 spring rates. Now, the spring rates that I see on almost all of the street S13 coilovers are F8kg/R6kg. Now, I don't know exactly what the kg means since everything I have been researching has been 200-250.

 

Now, this will mainly be a weekend driver and won't see more then 2 days of Auto-X or track use a year. Its just a nice car to have for me to drive down PCH during the summer months and one that I enjoy driving but want it to be a little stiffer for a more precise control feel.

 

As always your insight is greatly appreciated!

[New-to-240z]

Nobody knows? I've done searches and it is saying that 1 kg/mm = 56 lb/in and I did the numbers and that comes out to ..

 

Front : 8kg = 448lb/in

Rear : 6kg = 336lb/in

 

Now, I don't know if that's correct numbers since I've been seeing nothing but 200-225 Front and then 250 Rear. Seems that those are much stiffer then most people's setup for their Z's. I'm just trying to see if I should have them replace the springs with new springs and re-valve the shocks. I don't want a STIFF as nails ride, since I can't seam weld the car, and I don't want anything bad happening to the frame. I'll be getting a roll cage and strut bars, but that's about it for the chassis.

[B00STDZ]

You can run spring rates like those.. get some stout aftermarket struts with adjustment and get ready for a rough ride if you seem to run over any imperfections in the pavement.

[New-to-240z]

Well, the shocks are already included in the coilover package. I'm just wondering if I should have the maker of the coilovers re-valve the shocks as well as replace the coils with something in the 225 and 250 range. I haven't bought anything yet but everyone on this site is usually very informative.

 

I know that AZDAN has created the coilover adapters for S13 to S30 vehicles, and they accept the Megan Racing coilovers as well as the Stance coilovers. The stance and Megans are the same spring rate, but I just want to be sure that its a good idea to go with that stiff of springs for the Z's lighter body, as well as having the SR20DET make the weight a little lighter on the front shocks since the engine is moved so far back in the engine bay.

 

If anyone can give a little more insight to this I would truly appreciate it.

[B00STDZ]

I would go with 250 front, 275 rear...

[Drax240z]

For a weekend driver with occasional autocross I wouldn't be going much higher than spring rates around 200/250.

[New-to-240z]

Drax,

 

Do you know if it is even worth it then to go with a coilover setup from an S13? The reason I was thinking of going this route was because of the range of adjust ability. I can request whatever spring rate I want from the company and they will provide me with the springs as well as re-valve the shock for them. I know I can get the ground control coilover kit, but I was thinking that pre-load adjustment, as well as height adjustment would be a good idea, rather then the GC setup which doesn't allow for pre-load but instead just allows you to drop the car.

 

The price would end up being about 300 more for the full coilover option, but is it really even worth it for me?

 

Also, thanks again for the help.

[Drax240z]

For what you want out of the car, a ground control setup with good struts should do the trick nicely. Lots of spring rates available.

[New-to-240z]

so you're saying front 200 rear 250?

[johnc]

OK... what we are really concerned with is wheel rate, not spring rate. Spring rate is a way to achieve wheel rate as related to suspension frequency. A 240Z street/autocross/track car a suspension frequency in the 2hz range is good which means front spring rates around 250F and 275R (assuming stock vehicle weight and balance) and gives a wheel rates of 235 and 258. For a street car that's occasionally run at an autocross or on the track a suspension frequency in the 1.9hz range gives a reasonable ride with some handling benefits. That would be spring rates like 200F and 225R with wheel rates of 188 and 210.

 

If you look at the motion ratio of the S30 rear suspension you might find that the wheel rates are very similar to what I posted above so shock re-valving might not be needed.

[New-to-240z]

Damnit John, there u go sounding way too smart again!!! so, u are saying that if I go with the the ground control setup then I should go with 200F and 225R with standard Illumina shocks.

 

Now, With the numbers you are giving me and the calculations i have found on the net (200/56= 3.57kg/in) for the front and then (225/56= 4.017kg/in) for the rear.

 

It is sounding like it is a better move for me to just get the GC setup. I don't know if the coilover maker (stance) would be willing or even able to provide me with springs that soft and then re-valve the shocks for them.

 

Its just hard because I am on the edge of going with an entire rear and front conversion to S13 parts . . . or if I should just go with a TTT rear end conversion. The price is almost the same except that the S13 conversion is actually about $400 more, and if the car is ever crashed no $$ can come from it. Where as if the TTT conversion is thereand the car is crashed, the parts can be salvaged and re-sold assuming they are in good enough condition.

[Drax240z]

I was trying to keep it simple... Granted changing the suspension layout to S13 hardware could modify the motion ratio between wheel and spring, and modify the wheel rate when compared to the stock setup. This discussion is also incomplete without talking about swaybars, tire selection, as well as dampers.

 

I run 200f/250r with a 1" front bar, works well for me in combined driving. Is it that simple? No, weight, differential type, power band, my local track, etc. all played a role in me getting to that point. Does it work for MY setup? Yes.

 

Sounds like the setup you want doesn't need the wheel reinvented, I would stick to what works well for many, many Z enthusiasts. Coilovers, decent dampers, and spring rates as discussed forever on this forum if you use the search.

[New-to-240z]

Well . . . I will take all of this into consideration and will probably go with the 200/250 setup. No need to go with aftermarket coilovers for an S13 if I just get the TTT rear end conversion.

 

But, if the S13 suspension modification system goes through then I will work with the coilover manufacturers to see if they can lower their spring rates and at the same time re-valve.

 

So, here's to hoping for the best and we'll see how things turn out.

 

If anyone has anything else to include please do let me know. I can always learn more from this site and its users. Thanks again to everyone who has responded. It makes this conversion and thought process much easier for me.