Track: Sebring
Car: C6Z
Wheels: CCW18X13R 18X11F
Tires: A7 345R 315F
Coilovers/Dampers: JRZ w/eibach springs (#950F #650R)
Swaybars: GMP. T1. Setup - Front = Stiffest. Rear = Softest
Aero: Katech CF (lip, tray, skirts, rear oversize spoiler)
Cornered and X Scale balanced with driver
QUESTION:
1 - Where should the ride height be? (Measured from?)
2 - What should be the rake (if differ from sum of question #1)
3 - Should the spring be pre-loaded? If so, how much?

Thank You,

 

Anyone?

 

Someone been there ...done that..

 

What the heck I'll take a whack at it

IMO your spring rates are a off.

With coil-overs you typically want to have a stiffer rear spring than front

Examples:

LG coil overs: 600 F 700 R
DRM coil overs: 450 F 650 R
Pfadt coil-overs: 425 F 575 R

So if you are indeed running 950 F 650 R that would seem to be quite a difference from the norm. That being said here are some ride height specs:

Floor to the top of the fender arch = 26.4 front 27.3 rear
Floor to frame just in front(front) and just behind (rear) the tie down points on the frame = 5 1/8" Front 5 9/16" rear
Trim heights measured with GM trim height tool = 31 mm front and 99 mm rear

Best way to measure "ride height" is to measure actual trim height who cares about the way the car "sits" I want my suspension to have proper geometry - it is nice to have multiple places to check - just to make sure you're in the ball park though.

The amount of spring pre-load depends on what it takes to get your A-arms to there desired angle.

 

Thank You.
RE: Spring # ...I was told to go with larger/heavier in front due to motor being in front. It was my understanding that larger front springs in front will handle the dive better...maybe I was given wrong advice.

RE: Trim...Can you explain where and how to measure? What's the cause and effect?

Thank You

 

I approached it from an anecdotal perspective. Rode with and talked to mechanic drivers that win races in C5's like mine. I am happy with 1100# up front/840# in rear, adco bars, lowered with poly's and running with 315/18 R7's. Works for me.

 

Leaf springs right? Big difference from coils, different geometry.

 

1100/840 makes sense..as with 950/650 under hard braking and heavy cornering my c6 still dive a little (loading) while the rear unloading...hence the car is not as flat at the corner as I would like it to be.

BTW - what is your ride height from from frame rails down?

Thanks

 

Correct; leaf springs. I have gotten some input from national competitors that the coil overs may not be the best with the C5 geometry. I am on my second aftermarket leaf in front. They do wear out, of course, but they do a great job. Not sure of the ride height. I measured the frame rails after a good corner weighting but don't have that handy at the moment (another state). The height is non existent more like how low is it draggin!

 

You might want to read this thread:

https://www.corvetteforum.com/forums...al-thread.html

What is your racing background? How much experience do you have in a corvette? What tracks have you raced on? Are you setting track records or running in the middle or back? Or just out testing alone? Who is building your car and setting it up? Do you/they have any prior experience setting up a track car to go fast? This info might help determine how much help you need. It's hard to tell on a forum. It's taken most of us years to get our cars setup the way we like and it's always a work in progress. It's hard to just say "do this or that" and you will be fast. Plus you might want to know who you are getting the info from in the first place. A hpde guy who is regurgitating info he read on a forum somewhere, a DIY club racer (may or may not know anything about setting up a car properly or optimally), a vendor trying to sell something, a pro driver, or a pro engineer (with or without experience on a corvette). Free info might not always be the best and you will get dozens of different opinions. Be careful making big changes from the norm as they are likely to make your car slower and more difficult to drive. I would start with a proven setup and make small changes from there based on personal testing. I'm not sure if making your car flat in the corners is the best goal. Try to aim for maximum mechanical grip and balance.

 

Yep more than one way to skin a cat. But coils certainly can and do work and you have the flexibility to easily change rates to get them where you like. Plus you can change sway bars as desired. I can assure you my car handles as well as any C5 or C6 out there and I run coils. I'm sure leafs work equally as well but they will require different spring rates due to the different geometry and pick up locations.

 

Good advice. I have to say that I learn every year of tracking. For the last couple of years I have experimented with different 100 tread wear rated tires while trying to get the most out of track time with a fair trade off in performance. I would watch aero cars pass me bye as I tried to keep the gap close. My steering rack expired the first of this year so I had a rebuild from TurnOne. I then put on a set of R7's. (FWIW, 18's square with 295fnt/315rear) Guys, the turn in rate and grip are phenomenal. I don't think I'll ever need aero. However, I probably need to budget for SKF's every year.

 

I'll second that...southernson's car is hooked up. He graciously gave me a few hot laps at NCM this past weekend and it plain scoots! His setup appeared to be very well balanced and never once did I get the impression that he had to fight the car.

 

Hey, Todd! Enjoyed riding with you, buddy. You showed a great deal of car control discipline for someone relatively new to the sport. I was impressed. You have the ability to advance as quickly as anyone ever has. I was particularly impressed with your ability to acquire verbal input at speed and execute it on the next lap. Believe me, not everyone can do that.

 

Car is corner balanced by pro shop which include my weight in it. Judging by tire wear and temp it seems grip is ok but when I corner hard/faster the inside rear seems to unload too much hance I believe I loose grip. Example: Sebring turn 7, 10 and 13 the car will slide on all 4 wheels (at least it feel so in my toosh).
So, I'm thinking of a way to keep the inside rear from unloading so much.

 

Thanks.
I guess what I'm trying to fine tune is the inside right rear from unloading too much. Hence the car is outside heavy.

 

Stiff spring and stiff sway bar on front is the usual prescription for keeping the inside rear grip. If the front outside gets body roll (weight transfer) the inside rear will unload. This is experienced even with no braking into the turn because the scrubbing off of speed rolls the body weight transfer to that corner. Worse with greater COG height, of course, as you have alluded to. You might even try to unfasten one side (either side) of the rear sway bar.

 

Keep in mind that the spring rate is not what matters, it's the wheel rate. That's where there is a big disconnect when comparing coil overs to leafs. Because of the angle of the rear shocks, to get the same front to rear balance with coil overs compared to leafs, you need more rear spring than front, but not by much.

 

We agree! I have 950#/650# spring with T1 sway bars...Front sway at its STIFFEST and Rear at its SOFTEST. I'm thinking going to heavier spring in front would be the solution.
Unless there is a stiffer bar out there ....a Pfadt bar would have been nice.

 

MORE REAR SPRING? That is profound...PLEASE explain to me how more rear spring in coilover will help me keep the right rear from unloading as I mike a hard right...as it seems the right body corner and the outside of the tire are both shifting too much to the left..."rolling out"

Thank You...