nskyline34

Hey everyone looking for some advice here on setup. C5Z with Carbotech XP10’s, centric rotors, and braided lines all around and NT01’s (275’s and 305’s) with stock suspension. Coming into a turn (mainly 70mph+), squeeze on the brakes for moderate/hard braking (not even running deep in the turn), and the car has a lot of dive and feels like the *** end starts to get a little loose. I was just testing things out on some back canyon roads to just make sure things are dialed in for the start of the track season, and honestly it’s not exactly a confidence inspiring feeling. I would not like to see how things feel if I did this at 140… (Obviously I’m on the street so not going to find out, but on the track I wouldn’t be too excited to try it the first time).

I didn’t have this trouble when I ran XP8’s all around, but they also have a lot less bite to them than these 10’s do. Car isn’t hitting ABS when this happens, but I’m wondering what I can do to help resolve this? Am I starting to get to the limits of stock Z06 suspension in this scenario? (Cornering I’m still not consistently using all of it, but I feel like under braking now I am.) I’m just looking for a little guidance if I’m doing something wrong, or if this is just what happens with stock suspension, stickier tires, and better brakes? I know a lot of people run XP12/10 setup, so do they have this problem too?

I’ve been thinking about a stiffer front spring and some ’04 Z06 shocks and maybe some T1 sway bars, is it time for this jump yet or not?

Thanks for the advice fellas!

Andrew

redtopz

Yes, Randy Pobst calls that the corvette flop . Not good for braking or corner entry. Stiffer front springs, sway bars, and more shock rebound in back will help.

nskyline34

Ok, I'm glad I'm getting a little validation here. Racing shifter karts this was never a problem - so I'm learning.

If I just did a stiffer front spring and did NOT do anything with the rear spring, would this upset the car's handling/balance? Also I'm strongly considering sway bars. The car is 70% a track car and 30% a street car. I cannot decide if the T1 bars are worth the $$ or if I should just go with a good upgrade like a Hotchkis or something similar?

I'm currently running the stock shocks, I was considering going to the 2004's, would this be worth it?

Thanks again!

ArtClassShank

I'm no track expert, so grain of salt etc etc.


But I have noticed this lightness under heavy braking, interested to see what others chime in with.


As far as shocks, based on my research, you'd be better off with C6 ZO6 shocks. More cost effective and newer tech makes it a better deal IMO. Only drawback I can think of is the dampening rate in relation to the springs. Not sure how different a C6's rear spring is in stiffness compared to a C5. Mines an 04 so I have these shocks, can't comment on any other cars.


Or you could subsidize my upgrade and buy mine when they come off?

brkntrxn

What year C5Z? While I agree with Bill, you may just need to replace the shocks from age, versus an entirely new suspension.

nskyline34

It is a 2003 and as far as I know they are OEM. Car only has 20k miles on it though.

mountainbiker2

There's the reason. You know have suspension. I never experience this front end dive in Autocross. I think the front spring is fine for most drivers. If you want to change, just go with coilovers.

Steve

UstaB-GS549

Check your rear toe. Any toe out under braking makes car unstable.

tungstenfoot

I would check your caliper slides and make sure they are moving freely and lubed. Checking rear toe is also good idea

SunnydayDILYSI

I had good luck with the Bilstein sport shocks. Relatively cheap (I think it was ~$400 all in and not too difficult of a DIY job). It worked well for me with XP10s, RP2s, and XP24s. Never had to do a stagger front to back. Was using stock C5Z springs at the time. Similar tire sizes and types (ran NT-05, NT-01, and R888s that way).

brkntrxn

For context, I purchased our 2003 Z06 in 2009 with 24k miles and changed the shocks within a year or so to 2004 OEM shocks. Shocks will age out, in my opinion.


Darn good suggestion of something to check. In addition, check front alignment to ensure toe-out or caster isn't so significant that the car is tramlining with pavement undulations under braking... making it feel like the back is walking.

The other thing that may make a car squirrely under braking is too much rake in the car. If the rear of the car is already jacked way up (or front is way down), it will exasperate the weight transfer during hard braking. For a stock car with stock suspension and no aero, go with 5/8" - 3/4" rake from front to rear.

An additional data point is as you go up in pad mu, you may need to alter your braking actions. The more initial bite a pad has, the less you need to stomp on the brake pedal.

Before the NASA rules changes, quite a few of us went VERY fast with OEM C5Z06 leaf springs, 04 shocks, and calipers with lightweight aftermarket sways and pads such as Carbotech XP12s front and XP10s rear (or 16/12s and even 20/12s). I say that to say, check the basics of the setup before throwing money at the car.

nskyline34

All great ideas fellas thank you. I will have to look at the alignment on the car. I have the spec sheet from the shop that did it (I know I know rookie move, but I'm learning). I want to be able to do the aligment myself, is there a good setup out there for a modest amount of coin? Otherwise I was thinking about machining my own setup, shouldnt be too terribly difficult...

Karts were nice not having to worry about suspension, but you did play with axle diameters and chassis stiffness (you could remove bars and replace bars with thicker or thinner ones to change things). But its all in the progression right?

There isnt a lot of rake in the car at all, but I will definitely check this too. Didnt event think about that.

And yes, stomping on the brake petal is the best way to make a car drive like garbage - that's why I said "squeeze" on the brakes in my OP. Just to let people know that its progressive. The initial bite isnt the issue, if you get on the brakes hard and wait for things to settle it still feels like it. Its not something so severe that you can catch it on a camera I dont think, but you can feel it in your butt and back.

I REALLY agree with that last sentence... no point in throwing money at something. You waste the money and you dont learn nearly as much - that's why I'm asking you experienced fellers!

nskyline34

One thing I have been curious about is going through and replacing all the bushings with poly. I know that this wont help my current problem, but how much will this help the car overall do you think? Just make things feel a little more solid? Or would I be better off with a set of swaybars (really want to level things out). I feel like the NT01's when up to full temp are a little too much for the stock suspension so might help to stiffen things up?

Just wondering.

edge04

I once switched to XP24 fronts and 20 rears and had to completely adjust my braking style. Way too much initial bite. If I came close to stomping on the brakes the car would turn evil especially in the rear.

Sox-Fan

Kind of interested to watch this thread and convenient timing, too. I've been working with Sperkins, chasing the same issue with a C6z.

nskyline34

Very interesting to know. I can completely understand how that would happen, but at the same time it felt like the *** of the car was 3' in the air and the front bumper was dragging. Was somewhat shocked at the amount of weight transfer.

I have a strong hunch it's the rear toe honestly. Wish I drove the car to work today so I could go check in my book and see what it says.

I'm going to design and machine a bunch of tooling so that I can do my own alignment this week if I can finish my current design project quickly... Unless someone can recommend a kit that will allow you to align all 4 corners camber, caster, and toe? Not opposed to saving time and just buying something...?

SunnydayDILYSI

If you are going to track the car, and are looking to make an investment in alignments, I strongly recommend investing in a camber kit. The stock hardware moves when you spin out. With the camber kit, you set and forget. It's literally a set of metal shims and you put on the size of shims that you want based on the level of camber. Once you bolt it on, nothing to come loose any more. But to change it you have to loosen all the bolts, change the shims, and realign.

brkntrxn

Poly/delrin bushings or sphericals definitely help, especially if the stock rubbers ones have walked out of the arms or are trashed. I'd definitely do sway bars before bushings, unless your bushings are degraded to the point they are visibly crap.

Is you car still full, OEM weight? Have you removed any weight and from where if so?

brkntrxn

Well there is your first problem!!!

Moto One

Check to make sure that you shocks compression / rebound are match, same with wheel weight, and that sway bars are not preloaded to one side or the other. Next tire pressures (I know simple). Also mention, check brake calipers (a binding one can reduce clamping power). Make sure that the front spring failing (it could happen).

Mark.