trapp

I have a 2009 C6 Z51. I went to slightly lower profile tires..

Stock 245 40 18 front
285 35 19 rear

new 245 35 18
295 30 19 with R6's

The car lost some height so under moderate or hard cornering and braking I'm scraping the front undercarriage plastic air deflectors. I only have about 1 inch clearance in the front from the plastic air deflectors . I have a procharger with intercooler that sits low...this is what I'm concerned about ..it only has about 2 3/4 inch clearance.

Can the suspension be tightened down to prevent too much diving so I don't bottom out...if not I'm afraid to run my new setup on the track...

Anyone have an idea how much my suspension will 'give"....more then 2 3/4 inch?

any thoughts

davidfarmer

the easiest thing would be to raise the ride height. Stiffer springs/shocks would also help. If you actually want to reduce "dive", then you need to remount the control arms to change the roll centers.

You raise the front by turning the adjusters in each end of the leaf springs. However, unless you intercooler is lower than the steel radiator support (nerf bars) you are probably safe. If it hangs below that, you WILL hit it eventually regardless.

hamdog

What brake pads are you running? If you're front pad coumpoud is considerably more aggressive then the rear, you'll get nose dives.

trapp

dtc 60 front
dtc 30 rear

John Shiels

The car is to low. Stiffer supsension and drop spindles is another option $$$$$$

AU N EGL

there is part of the problem

DTC 60s are race pads DTC 30s are not

Use DTC 60s front and rear.

plus if your planning more and more track days, an upgrade to the C6Z06 suspension or stiffer many be in order

gkmccready

The C6 Z51 front spring is the same as the C5Z front spring, and only 5# (or so) less than the C6Z front spring. So that isn't really going to help the nose dive much. More rebound damping in the rear, matching brake pad compounds, more bump damping in the front, or just a stiffer front spring would all help, though.

FWIW, I had PFC 01 / PFC Z pads the first couple of track days and the nose dive was crazy. When I ran matched brake compounds F/R the car was MUCH happier. I didn't really care for the KONI 3013Sports I tested on the car, but the ability to crank in some rebound certainly helped. I am pleased with my DRM [non-adjustable] coilovers...

0RAAMaudio

It does seem your car is probably to low so if you want to go faster on the track you might need to raise it up to where the geometry is correct. We cannot lower these cars much without giving up far to much in handling.

Though some run their cars really low and seem to feel they work well for them if all things are set correctly with a higher ride height(correct height) the car will be faster and should be easier and safer to drive fast in all conditions.

Brake pads, I generally run one compound softer in the rear with no issues but have not tracked my C6 yet, it seems your are quite a bit different. You can run much bigger calipers in the front versus rear on most cars, bigger rotors as well, deals with the heat better, and match up the compounds to the task.

If you still have the problem and do not want to change springs then at least some adjustable shocks could help, keep stiffening them up until the problem gets better though this is a bit of a bandaid approach.

hamdog

0Vector Vette

Trapp,
The differance in tire size is about 1" in diameter, so you lowered the car approximately 1/2". That can be raised up with the spring but you will need to do the rear as well or your rake will be off, assuming you went to lower profile in rear as well. Most likely your issue will be resolved with equal brake compound on rear. I always run the same compound on front and rear. GM already adjusted your brake bias.
Robert Finlayson
Performance AFX Motorsports

trapp

I would like to thank everyone for all the input on my posted question. I can always count on great advice from this forum.

Follow-up: I took the car to gingerman yesterday. I removed the front plastic air-dam...and tried some slow laps to see if I was going to 'bottom out" on the procharger intercooler craddle ski's... well I didn't. I ran harder and harder until I was full bore and NO touching to the ski's of the craddle. I am only 2 3/4 off the ground but somehow I never touched. The craddle is set-back from the front end somewhat and does not extend out near the wheel side to side so I guess I'm ok.
I will start running DTC 60's all around. That probably will help.
I would like to go to stiffer springs all-around if possible...I feel too much floating around which makes me less confident about higher speeds.

comment: This was the first time on R6's from Kumho XS's. Wow what a difference. I was so much faster through the corners..alot of fun.

thanks again

trapp

John Shiels

You may not be hitting but I bet your handling can improve with less weight transfer to the nose under braking.

rustyguns

i run dtc 70's front and rear! works great!

rustyguns

put a T1 spring in the front with a T1 sway bar and you will be lovin' it !

2K3Z06

That floating at high speeds, could be when the suspension is hitting the bump stops.

trapp

It just seems too loose ...or lose its tightness or stability the faster I go..braking from 120mph or more doesn't give the stable feedback I want...

Sway bars and stiffer springs maybe in order..

trapp

would stiffer springs do the trick?

hamdog

R compound tires are very pressure sensitive! Check your tire pressure immediately after the run to make sure you are under 40 PSI. High pressure can give you the floating effect. I should say, incorrect tire pressure in general wether it's low or high can give you that effect. It's unnerving!

John Shiels

Floating could be a mismatch of the springs and shocks due to selection or shock failure. When I had some real stiff springs and shocks that were not matched that was scary enough for me to quit after two laps and drive up the trailer.