Hi Everyone,

I am running a fully stripped and caged 350z (~2800lb). I also have a true coilover setup with Buddy Club Spec Coilover Kit. I am running 10k front and 8k rear.

The rear feels light, and I am prone to oversteer. I am currently running a square setup on 17x9.5 wheels wrapped in 255/40/17 Federal RSRR.

Anyone else have a similar setup with different spring rates?

 

That is way too stiff of a rear for the front rate in coilover config. Most people run a 4-500lbs split in true coilover.

Do you know your corner weights?

 

To give you an idea that is the equivalent of running a ~1000lbs rear spring in OEM config, assuming a few things.

 

I run a 12 upfront and a 8s in the rears, about 150lbs heavier (mostly upfront) and I dont feel that my back end is loose (albeit Im not tracking). Do you have adjustable sways and/or the ability to adjust up your rebound rate?

Interested to see what others chime in with?

 

^If you tracked your setup, it would be loose. In terms of OEM spring position you are both running rear rates that are *significantly* higher than the fronts (like almost twice the rate eg. 560f/1000r, or 672/1000r). Typically aside from the kits that have "drift" in the name, you really dont see these kind of rates being used at the track. Im not saying that they cant be made to work either. That is why it is so important to

Corner weights need to be taken into account otherwise this conversation will just be a SWAG.

 

^one thing that factored into my decision to go 4k difference is that my rear end is lighter than an OEM setup ... I dont know 'exactly' where I'm at but most my weight reduction has come off the middle and rear of the car, furthermore, most my additional weight (turbos/headers/IC) were added to the front of the car. The decision to go 12 f / 8 r is that I pick up a 10k spring and I can go 10f / 8r or 12f / 10r and see what I like.

Lastly - All I know is that I know almost nothing - if I knew a little more, I'd know nothing.

 

 

impressive still ... especially considering you have a cage.

 

 

I assume those weights are without you in it. They need to be with you in the car and actual weights, not just a swag, in order to make the calculations meaningful.

Either way you are going to need to drop that rear rate by quite a bit...5k (280lbs) is a good number for that level of tire (roughly 625lbs OEM spring equivalent - some go softer yet depending on tire aero tracks and driver preference). Though it still wont match the 10k front rates and youll continue to have a "loose" car at the limit. I would be looking at 14k front minimum in addition to dropping the rear. Really, you should just get a new setup bc with those dampers, who knows.

 

 

A 12/5 split with those corner weights will put you at almost even front and rear frequencies, which is generally to be avoided by conventional wisdom...thats why I suggested the 14kg/5kg split. But I do understand wanting to work within your current damper, so if you do go with 12kg front it may be prudent to go with a 6kg rear even though it is on the looser side, to stagger the ride frequencies slightly. By the rough numbers though, esp without exact corner weights and other variables. And this is one of those areas where the devil is definitely in the details. But unless there is money on the line were just having fun anyway right.

 

My car is heavier than yours but I'm running a 14/7 set up with Swift springs on Zeal coil overs and been happy with it

 

Lol, so true. I am but a grasshopper. Im at 55r/45r...but cross is what matters. Have you seen how 991s scale out?...50% cross, yet 37/63 rear weight dist. For street driving in reality almost anything will work as long as the damping matches and you arent bottoming or topping out. In a perfect world, one would modify spring rates to suit specific tracks and conditions, which does happen in addition to modifying spring preload and gas pressure.

 

I appreciate the time you put into this thread ... it's helped thus far!

 

Update:

I have confirmed that my rears are actually 6k, but my fronts are 10k.

We corner balanced the car today, and got the cross weights at 50/50. The front/rear is 54/46, however, so I need to get some more weight back there. The car weighs 2880 with 1/2 tank of gas without me in it.

I am planning to reroute the battery to behind the passenger seat. Would 12K front springs help move weight to the back?

 

 

 

 

Spring rate changes will not alter static weight dist.