True Rear vs. Divorced spring (causes damage?)

Hotrodz

LMAO, you have not been on the forum very long and made a handful of post. I am not sure how long you have been tracking and your depth of knowledge with the 370z platform but your post in naive. First off you don't need to do a wind tunnel for all things aero. It is common knowledge that lowering the car and adding a from splitter and having some type of rear spoiler will help. I have been dealing with FA for several years and their product is nice but some of the advise is suspect on spring rate recommendations. Lastly, because of my aero I reached out to a aero consultant to help me dial in my aero and suspension. There is a thread dedicated to that discussion in the track section of the forum if you want to increase your know and whole lot of discussion about spring rates for divorced versus true type setups. Therefore my advise is not without consulting a professional or others on this forum that have equally as much knowledge. So the rule of thumb is with a true type setup you don't want your rear spring rates to be much more than what you have for a divorced OEM spring rate, maybe slightly higher. Good luck and I hope you don't have a negative outcome because your rear spring rates are too stiff. I think the track is the best place to try out your new coils as it is a controlled environment and on the road if things go wrong it could be fatal to you or someone else. I hope it all turns out the way you want.

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16nz34

Yeah, might be a bit naive for sure. I don't claim to be an expert in any of this and rely pretty heavily on the experience of others. I ran about 17 track events last year with no aero. The only track where I experienced some "interesting" handling characteristics was VIR as I was able to get the car up to about 140 mph going down the back straight and into the roller coaster...I could feel the car getting a little "floaty" in the braking zone, probably due to the speed and the fact that I have neither a front splitter or a rear wing AND was running the OEM shock and spring setup.

Here's what FA asked to determine the spring rate:

Year/Make/Model
Type of Driving (i.e. 90% track 10% daily)
Track Surface - Smooth, Bumpy, Both
Brand,Model,Width Tires
Other Suspension Mods (sway bars, bushings, etc.)
Motor Swap?
If heavily modified, weight of vehicle?
Aero Mods (front splitter, rear wing, rear diffuser, flat undertray)
Roll Cage? Y/N
If roll cage, welded or bolted?

So, I answered all of those questions and they came back with 14k front, 10k rear. Now, I suppose I may need less in the rear, but changing springs can't be that expensive or that hard, no? As for trying all of this out, yes, my performance mechanic who will be performing the corner balance and alignment already warned me to take it very easy the first time out with true coilovers as the car will be completely different than the standard OEM setup. He already availed me of numerous stories of people who did not take his advice and ended up with very wrecked cars. I am lucky to have a very good track close by that offers "lapping days" where you get about 4.5 hours of track time and can go out and test various setups on the car. Definitely something I'll be doing before I even attempt to run this thing at any other tracks in my area.

I get it. There is A LOT that goes into the suspension and aero setup of a car.
You've got spring rates, swaybars, alignment (caster, camber and toe), shock compression (high and low speed), shock rebound (high and low speed), tire pressure and brake bias. All of these impact how the car handles. I don't profess to be anywhere close to an expert in all of this and also know (from experience) that even a small mistake in our "hobby" can have disasterous results.

I'm sending a followup email to FA to see how they go about determining the spring rate and if indeed need something softer in the rear. However, given everything that goes into suspension and handling, I'm guessing that one could also compensate for a slightly firmer rear spring by adjusting other areas of the suspension?