Aero and Suspension Tuning With True Type Coilovers
 

So I have been doing some research on adding a rear diffuser to my current setup when I ran across an article/blog on the Professional Awesome Racing website https://professionalawesome.com. After read their article on aero and downforce I decide to shoot them an email to see if their splitter diffuser would be a good addition to my front aero. Long story longer we have exchange sever emails regarding my aero and suspension most significantly my spring rates and the owner Dan O'Donnell provide me with the following information:

So you have a “true type” rear, meaning the spring is directly on the damper body, not in the stock bucket. This has the effect of dramatically increasing the “wheel rate” or effective spring rate at the wheel, if you are using the same spring rate you use previously. If you are running 14k front 12k rear or 800lbs front 700lbs rear, the car will oversteer badly. I just had a long discussion with Savanna Little and Kevin Parlett. They are using a “true type” design as well on similar chassis designs and no suspension manufacture compensates properly for the change.

With your rear wing, I think you can safely add our diffusers and vents, but I would really, really want you to change spring rates to a proper setup. Your system is borderline unsafe in my opinion. Let me know if you want to do the calculations to get the right springs in there. Quick math is lettings me like if you have 14k front springs, you need to be around 5-6k in the rear.

So I am prepared to pay for the his consulting fee as this a steep learning curve for me and at my soon to be power level I don't want to be wadding my car up or possibly hurting anyone else. Here is where I need some help as he needs some information from me to dial the best spring rates for the rear coilovers. I need to provide him with corner weights for the car and obviously right now I have no way to do so. He doesn't need to have actual numbers but just need to be in the ballpark. My car weighs about 3440 with me in it and I am 210 lbs. If any of you have corner weight numbers and your car is of similar weight I would greatly appreciate you providing them to me.

Thank you in advance and go check out the Professional Awesome Racing!

Cheers,
Bob

That's my corner weights I have the stillen charger with the topgunz cooler up front https://uploads.tapatalk-cdn.com/201...bf36186327.jpg

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This was my car, after SPL arms and true type rear conversion, with driver a driver between 120lbs to 140lbs, and maybe half tank of gas. Stock motor, no bolt on power mods. 265/35/19 in front instead of the 245/40/19.

https://vorshlag.smugmug.com/Custome...ed/i-ktQMxz4/A

Thanks for the info!!!:tup::tiphat:

No problem hope it helps

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Keep them coming!

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I went through their downforce guide and it is very helpful, I got convinced into getting only front splitter and rear wing for my planned aero, as they are the most simple and effective way to gain more/cleaner downforce.



and here is my car weight, very close to your car weight, but I think with half fuel tank.

http://www.the370z.com/attachments/m...2019210657.jpg

Also, about spring rates, this is something I noticed when I got my mca reds, there was a big difference in front and rear, 21k/7k, when I had my rear height higher than fronts by around an inch, the car was nearly neutral, but when I tried with lower rear, around 0.5 inch higher, the car understeered at exit but my turn in was great. Many factors could affect understeer/oversteer, it could be adjusted easily unless it is undrivable.

Thanks for the information and yes Dan has been really helpful. I was only able to get one track day really with the true coilovers and it was kind of scary as I had two offs due oversteer. I could not trail brake because the rear end wanted to pass the front end as well. I don't know if I will end up as stiff as you are up front but probably pretty close to where you are in the rear. I generally run 0.5" of rake. It seems to work pretty well for me when go low with my ride height.

http://www.the370z.com/members/2011-...03-14-2018.jpg
http://www.the370z.com/members/2011-...-124201015.jpg
http://www.the370z.com/members/2011-...-124153936.jpg
http://www.the370z.com/members/2011-...-124146822.jpg
http://www.the370z.com/members/2011-...e-install.html
~190 Driver. Full list of mods.

Best of luck to you! After reading a few books on suspension tuning and car setup I realized I was out of my league and would waste track time getting it right on my own and hired a professional shop for race cars.

https://images-na.ssl-images-amazon....4,203,200_.jpg

Legend. Thank you Bob for all your wisdom, and insight. The devil's in the details, and aero balance in our naturally neutral / oversteery cars is critical to safely turning quality laps.

Oscar

With a true type rear suspension, it makes the motion ratio very close to 1 to 1. If you ran a 750lb/13k rear with the divorced set-up, that would put you at a natural frequency of about 2.00 hertz. If you were to then run that same spring with a true type rear, that bumps things up to over 3.00 hertz. Based on my calculator, you would need to go back down to 7-5k or 400lb to 300lb spring range if you wanted the rear to feel the same as when you were running the divorced set-up with 13k/750lb springs. I don't know how aero effects this as I have been focused on autocross, but I imagine you need to run on the stiffer end of the range since you have a force pushing down on the car.

I would love to see what he comes up with. Have my math checked so to speak.

Thanks bro I really appreciate your input. You have been very helpful here on the forum. I have found that I have reached my limit as well and there just are so many variables with suspension and aero once you move beyond the basic bolt ons.

Thanks you input as my friend as there is a lot experience on here singularly and collectively. I want to respect Dan's consulting and so I will let you know what he provides me given our agreement once I give him all the data he has requested. I will tell you this! Your calculations are totally in line with his rough estimate..."Quick math is lettings me like if you have 14k front springs, you need to be around 5-6k in the rear."

Cheers! :tiphat:

Sub’d

I have that same book. Tell you how long that book has been around. I used it to set up my TransAm's back in the late 70's. :tup: Still have it.

I've always had this questions in the back of my mind on this subject. I've seen a number of set-ups that the divorced set-up vs true type run close to the same spring rates. And some of this is from the companies that make true type. And suggest a spring rate too high from what Bobby is saying. Which I believe too. Thanks Bobby to bring this to light. :tup:

I am really happy that this is helpful. I really lucked out on finding someone that understands this stuff and can make sense of it to someone that knows enough to be dangerous and mean that literally.!:eek:

I remember reading about this

Where the spring is located is physically changed when u go from OEM type to true type
Since the OEM spring rates are based on oem locations, and the tuners are using that same geometry to do their math, it stands to reason that changing that spring location changes the geometry and requires new math to find ideal spring rates

I wouldn’t say geometry has changed. The arc of which the arms move are still the same. There’s no change to how camber and toe build up as the springs get compressed.

It’s the physics that changed. Imagine using the same spring, moving the spring outward to the hub makes it much harder to compress the spring, therefore a lower spring rate is needed to compensate.

Nailed it, as this is what I have read and was explained to me!:tup:

One thing to keep in mind is that while the geometry doesn't "really" change, it can be slightly different with respect to the angle the spring is acting on the suspension arms. This is why when calculating suspension numbers like motion ratio, wheel rate, and suspension frequency, you have to do some trigonometry with the angle the spring is at.

:tiphat:

I remember my first time reading a discussion about this on a wrx forum, it went over my head completely. Looking forward to the results. This thread makes me think twice about my own rear rate.

It is agonizing for me as I want to get the info, make the adjustments and test them but the testing will have to wait until my motor is built and installed. I still have ETA on delivery.:ugh2:

I should have corner weights when they set the alignment on my car. They are supposed to check them since I am corner balanced. I will get them to you when/if that happens.

Honestly, you should be ordering your spring rates based on how much downforce your car is going to produce at certain speeds. A bucket type coilover system, the spring is far closer to the hinge, so it needs a lot more spring weight to compensate. Running a true style, without aero, 6k is on the mark based on my research. I might want to bump it up to a 7k to compensate for your aero. Just my 2 cents. It would probably settle down the rear a lot powering out, under braking and on bumpy surfaces or rumble strips.

It sounds dumb, but chassis tuning on Forza, I drop the damper and spring rates a lot to settle rear down and add a bit of toe in. It's not real life, but I'd imagine the logic is the same.

Edit: Totally wrote this blind and happy others kind of confirmed my thoughts. I run stock Nismo aero and Swifts. I'm basic lol.

I feel like your motor build wait has been going on for at least 3 years.. cant imagine what it's like for you lol

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You are not wrong! That being said if your suspension is not set properly the influences from the aero can have significant impact on handling and that is why he stated that with the spring rates I am currently running and the downforce from the wing will cause the car to oversteer significantly because you are loading the rear of the vehicle and unloading or adding lift to the front of the vehicle. The fix will allow me then to do aero tuning that I need to maximize front and rear aero.

So my initial question to Danial at Awesome Performance Racing was did he think adding front splitter diffusers would be beneficial with my current setup and the whp I will be running in the future? He initially said no and then after I sent him information on my coilovers, he provide the information I posted and he asked me for some data so he could figure out the best spring rates for my Z. He specifically asked for corner spring weights and for me to give him the spring lengths front and rear when the car is unloaded and then compressed as this all matters when considering spring weight and drupe. The other thing to consider is that if your wheel rates are off you can over work your rear diff. This maybe one of the reasons some have issues with overheating their rear diff at the track or on canyon roads.

I figure if he wants to help me fine tune my car setup I am going to listen and take in all the information I can. His credentials and the people race team he works with speaks volumes. Oh and he said the diffusers would be beneficial.

LMAO it does feel like three years but it has only been since November last year.

Then help me out

This may be the first time I rated a thread 5 stars un-ironically.

AJ Hartman is another guy that I found that knows his stuff. All his products are CFD or wind tunnel tested. The first part of this video explains aero loading and spring rates.

Thank you sir and you have been rep!

Thanks. I’m going to use eddies go pro and try to capture some live data using yarn and tape to see how the fender vents and hoods vents work. Before going with aero and coil overs.

My car was 3416 lbs with me in it(180lbs) and a 90% full gas tank. Corner weights were
LF- 981 RF- 947
LR- 766 RR- 722

I have true style rears and plan to upgrade the aero this winter so I am also interested in what they come up with for spring rates.

Thank you sir and I will be adding aero settings after getting spring rates figured out.

Excellent thread Bob! The timing is just perfect for me since I'm just embarking on my journey into the realm of real aerodynamics. I'm pretty pleased with the splitter and canards i've got on the car now and after testing at Laguna Seca, I can definitely say that the aero was working. Cant wait for my wing to arrive. Need to read through the material on this site, seems like there's a lot of great info and guidance here. Thanks for sharing and im looking forward to hearing more about the development of your car with Professional Awesome Racing.

Glad to hear things went well at Laguna Seca. A front splitter and lowering the car provides for better turn in and cornering grip for sure. Which wing did you get?

I was expecting the car to be a little oversteery but turn in seemed to improve on the faster corners like turn 9 and 6. Corkscrew seemed to have gotten better as well, earlier on the throttle at the exit, flat out.

I'm getting the Ings +1 ZPower Ver. NISMO wing
https://ings-net.com/english/product...34_nismo_1.jpg

Beautiful wing! You may have to make some adjustments when you add the wing because of the additional rear grip. It may simply add even more traction because your car is well balanced to begin with.

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I've done all these things...what is is specifically you are asking here? A lot goes into it beyond basic geometry and "aero"? Aero is a wide term...