mobhouse

So for a few times now, I've been feeling my car start floating around 130 on up. I have different tires all the way around and think that it could be the reason. Running 355/30/19 and 285/35/19. Is this something common? Car only has 12k miles on it now.

SpnkbnkZ06

Sometimes the front tires follow grooves in the road and gives that floating feeling

outhouse

Floating feeling


DRM's cure it

mobhouse

na, it's not that. Happened to me at the drag strip and it literally felt like my car was lifting up off the ground.

Unreal

Disagree. Only if it is from blown shocks. Could be tires, tire pressure, alignment or a few other things. Once he checks and makes sure it isn't those, then shocks can be looked into.

Mordeth

DRM valved Bilstein shocks will help the car to feel more planted, but mostly on the twisties and over rumble strips.

What you are likely experiencing, assuming alignment and tires are to spec, is front end float. This is an aerodynamic issue. You need to create a low pressure area under the front of the car. GM for a variety of reasons (mostly gov't regulations) did their best but it can be improved.

What will help is a vented hood, a front splitter with a reinforcement inside the bumper cover, under-tray and lower the car approx 1/2" to 1". You could also remove the rubber guard located under the front of the car, that in my opinion does next to nothing. I cut mine right off. This will allow air to move faster under the car, and create a natural low pressure area there. This low pressure provides much needed front down force. It is a matter of fluid dynamics. Pinching the air by lowering it and using a splitter will force the air to go faster and direct it appropriately. If it also has a smooth path under the car it will reduce turbulence.

encasedmetal

mine feels that way on back roads. 33psi hot Michelins, stock alignment.

CorsoZ06

I know the exact scenario you are describing. My CTS-V did the same thing north of 130mph or so. First time I exeperience it, it really got my attention!! Everything with the car was within spec; alignment, tire pressure, tire condition, suspension, etc.

Soon thereafter I upgraded the suspension to the GM-supplied FG2 shocks which were a $1400 option when purchased with the car new. Very few actually came with them. Anyway, after they were installed this phenomenon completely disappeared.

That said, I wouldn't be surprised if the DRP Bilsteins solves this problem.

Unreal

I don't think it is an aero issue. Way to many stock z06s see 130+ on drag strip/straight line all the time without issue, with stock aero. Sounds like a alignment or mismatch tire/pressure issue.

If it is a "floaty" rear end in turns then shocks could help.

AzDave47

... unless you run the car hard using the brakes like HPDEs. The two reasons GM put that front air dam on was 1. to create high pressure (bad in that it creates lift) to force air into the horizontal brake cooling ducts to cool the front brakes and 2. create low pressure behind the air dam to help draw air thru the radiator for cooling.

On my car, once I installed 4" brake cooling ducts on either side of the grill and didn't need the air dam for brake cooling, I removed the two outside pieces and cut the center piece down about 1/2 to maintain some negative pressure to help radiator cooling.

With stock aero, the Z06 is much better planted at 190+ than '60's muscle cars were at 100.

AzDave47

OP, I couldn't find diameter specs on your tire combo, but you may have taken some of the rake out (front lower than the rear stock) and that could account for the float as these cars require a fair amount of rake for the aero to work properly.

The OEM tires have the fronts approximately 1.1" smaller in diameter than the rears. If you increase the rear to front stagger that should help aero stability some.

Lawdogg

As AzDave said, check your rake.

Mordeth

Agree with the brake cooling ducts. With your instruction, that is exactly what I did to mine. We all will agree that aerodynamic design on vehicles has improved over the last 50+ years. However, we are trying to improve it further, which is admittedly comprised in some areas by GM to meet CAFE and other government regulations, as well as budgeting limitations.

So I still feel that aero is at least in part, contributing to his issue. Many guys I see here spend time, money and resources on the motor and ignore the suspension, tires, aerodynamics and brakes. For a romp around town, or to impress the women on a dyno, this is fine. However, it is an oversight and the existing systems designed by GM can be improved without a lot of work. GM did not design these vehicles to regularly see speeds in excess of 120mph (or for extended periods of time), although they certainly can.

I routinely see speeds of 145mph+ in my C6 Z06 at the back straight of Watkins Glen. I too experienced the floaty, uneasy feeling that was not resolved with suspension or tire changes. After a proper front splitter, a reinforcement brace, slight lowering of the vehicle and a vented hood, the floaty feeling mostly went away. That is my own direct experience on a race surface. Your mileage may vary.

Additionally, both Katech and LG, who have raced C6s extensively, have performed and provided wind tunnel testing on our cars. It is very clear what happens when you address front aero with the above bits.

As mentioned, the rake is also important.

His rake is as follows:

Front tires 285/35/19. Convert tire width of 285mm to inches = 11.22 inches in width. Multiple by aspect ratio of 35% = 3.927 inch side wall height. Multiply by 2 equals 7.85 total inches of sidewall. Add wheel diameter of 19" gives us 26.85 inches of total height.

Rear tires 355/30/19. Convert tire width of 355 to inches = 13.98 inches wide. Multiply by aspect ratio of 30% = 4.19 inch side wall height. Multiply by 2 equals 8.38 inches of sidewall. Add wheel diameter of 19" gives us 27.38 inches of total height.

27.38/26.85 = 1.0197 ratio. Factory spec is approximately 1.04. So his is off, and his rake is likely not correct. So Dave is probably right that the rake is contributing. Go with a smaller front tire/wheel.

LoganExplosion

A lot of people say this. Mostly because they've heard it..

hrt vlv

aero. Side skirts will help. Dano will enlighten you with the facts.

outhouse

So you would argue they do not help plant the rear of the car better then stock working shocks not blown?



Sure but stock shocks suck exactly as OP described.


First day I had my car the rear was noticeably floaty at a 150 in the rear over the smallest pavement changes.

Unreal

Not in straight line. In a corner when upset, yes they control some of that "float" but not at all for what he is describing.

outhouse

Your bring up a great point.


The problem is dynamic to ones needs, and how the how car will be personally used.


In stock form the car is not meant to give extra stability at high speeds similar to needs of a tracked car.

Unreal

I can turn my shocks down and get it to feel floating in turns, but still perfectly stable in front line.

Rake has a huge effect on high speed stability. Swapping to larger front tires can easily cause this.

Find the actual issue, instead of the normal corvette forum solution of throwing parts at it.

Mordeth

Swapping to smaller front tires is the exact equivalent of "throwing parts at it". Not saying it is wrong, but is true.

In fact, lacking the proper equipment, such as a wind tunnel or a race track with supporting data logging and telemetry equipment, that is what we all do when we make changes to our car.

So we encounter a problem that is difficult to pin down the reason. What do we do? We use all available information, consult with others with experience in the area and then we "toss likely parts at it" until we find the solution. In an ideal world, with unlimited funds and unlimited resources and perfect data acquisition and perfect, repeatable circumstances, we wouldn't have to. You live in an ideal world? So we start with a problem, make a prediction on how to fix it, have a way to disprove it and then we "throw likely, simple parts" at it, and work our way up to more expensive, complex parts, doing our best to test and validate along the way.

Furthermore, if the rake is in fact the issue (ignore the active handling computer calculations due to ratio differences of wheel and tire size), then as I first stated, which you disagreed with and then apparently changed, it is an AERODYNAMIC issue. In other words, it is front float caused by insufficient rake (amongst other aerodynamic inefficiencies inherent to the C6 Z06). Not bashing the Z06, as I love it, but like everything it can be improved upon using tested methods.

By the way, there are a number of ways to influence the rake, beyond that of the sizes of the tires/wheels. For example, I can simply lower the front of the car (as I mentioned earlier), and create additional rake. Which is much easier, cheaper and faster than buying a new set of front tires and wheels to test the theory (again throwing parts at it). Yes this can create other problems, depending on how low you go, but it is one problem at a time around these parts.