Gearhead Jim

Vet-

I too am puzzled by my air dam clearance. The dam is stock, never "adjusted", never hit any really big road trash. Looks normal when I inspect it.



Thanks again for your numbers and comments, same for Boomer.

MisterMidlifeCrisis

2011 base coupe with F55. TPW was the last week in February. These are the measurements before I dropped it a hair:

LF: 27 3/8
RF: 27 1/2
LR: 28 3/8
RR: 28 1/2

Air dam was 3 3/4 inches!

Boomer111

Looks as if 1 1/2 inches of rake, give or take an 1/8.

I stated this rake number only as a reference to the previous posted heights, not meant as a spec rake number height.

Geez.....

JoesC5

A little info on how the Corvette's ride height affects the car's aerodynamics,

Measured in a North Carolina wind tunnel that the NASCAR guys use.

C6 base coupe, stock
.343 Cd
Add two people as their weight lowers the car,
.333 Cd


C6 base vert, stock
.359 Cd
Add two people as their weight lowers the car
.353 Cd

Gearhead Jim

That looks to be the highest we've seen on a stock setup.

Can you say about how many miles and months were on the car when these measurements were taken? I'm thinking they settle 1/4" or more, based on my own experience with adjustments.

Gearhead Jim

Very interesting, thanks!

MisterMidlifeCrisis

This was about a month or so ago, so the car would have been about five months old and had 5000 miles on it. When I lowered it, I did two turns on the front and one at the rear. It dropped about a half inch up front and scrapes a lot more, which worries me since I use the NCM front plate mount and that makes it so there's no give in the center portion. If I hit something hard, either the plate is going to bend or the entire center section is going to get torn loose.

Gearhead Jim

Thanks for the reply, but that destroys my theory about your car being high because it was new. Your car also had the least rake of any that have posted.

So, either your car just happened to be set incorrectly in production, or there has been a big change in how they are setting the height at the factory.

After installing my "lower" shock absorbers; I have twice raised my car by 1 turn on the bolts, each time initially raised it by 6/16". But after a couple of hundred miles and a week, the increase was only 2/16" - 3/16". Will your front will become "less lower" after more time? That would be nice, but somehow I doubt it.

Your current heights calculate to still be a little higher than mine, and higher than anyone else here except Vet who intentionally went higher than spec. Unfortunately, that probably means you are kinda stuck with the scraping issue. Welcome to the club!

Of course, all of this presumes that we measure our cars the same way. Minor "differences" from car to car, could be simply a result of how we hold the ruler.

JoesC5

When we measure the front wheel opening at 26.5" and the rear wheel opening at 27.7", the car does not have 1.2" rake. The rear wheel openings are larger then the front wheel openings(remember that the rear tires are ~1" larger in diameter then the front tires).

I measured my frame to the garage floor and have 5/16" rake from front to rear.

MisterMidlifeCrisis

I did my measurements basically using the centerline of the wheel since that seemed to correspond with the high part of the wheelwell. Even if it wasn't the high part of the wheelwell, it would be repeatable.

Here's a pic when it had just gotten to Ken Fichtner's. I don't think I have any other pictures that show the gap as well. I had a huge gap in the front, that was bigger than the huge gap in the back:



I don't think it settled down much from this picture.

I have a steep garage with one of those rounded transition curbs that I have to take at a significant angle. We've also taken our Vette on sandy beaches and gravel roads, both of which were a little bit of a problem before lowering and I'm sure would be a significant problem now. Maybe having it low is incentive not to drive in those conditions again!

Gearhead Jim

Correct.
I should have explained my language better, a 1 inch "rake" at the wheel wells will indeed leave the frame nearly parallel to the ground. But it's a convenient way to discuss the relationship between the wheel wells where we usually measure.

Gearhead Jim

Between our 2006 (sold) and 2009, we have over 80k miles on C6's with the Z51 suspension sitting at the factory ride height, whatever that was. I barely kissed one skid bar while pulling out of a parking lot too fast, and got lots of splinters and some underbody scratches from a big shovel laying on the road. And of course, the rubber air dam scrapes frequently on driveways, often the sides are worse than the center. That's all, and both of those events were in the 2006. I don't like gravel roads, but if the only road to where we are going is gravel, then I take it. I do avoid really rough stuff or deep ruts.

On our C5 (66k miles), we destroyed the air dam twice and cracked under the bumper on one of those events, from hitting big truck tire treads on the interstate; situations where traffic prevented us from dodging or stopping. Those events were the worst, but the damage wouldn't have been any less unless the car was at least three inches higher than stock.

So although it does take some mental adjustment to avoid problems in the C6, we've driven ours all over the U.S. without significant problems. But if the C7 is a little higher, that will be better .

MisterMidlifeCrisis

Jim, take a look again at the left front wheel, especially following the line made by the driver's A pillar. That looks like a truck sized gap to me! I've never seen another C6 that high or without almost any rake, which is why I dropped mines down a bit to try and get it closer to normal ride height.

I've got several weeks of dirt on it right now. Let me clean it up soon and I'll snap some after pictures to see if you think I'm close nor to "stock" ride height.

Gearhead Jim

I'm confident that your measurements are correct, it's my ability to see the difference that is wrong.

My feeble excuse is that I've got the Michelin PS2 runflats on my car, and those tires have a more rounded shoulder than the Goodyears. That makes my gap look bigger than it really is, so everyone on Goodyears looks like they have less gap than me. "That's my story and I'm sticking to it."

Gearhead Jim

Last night I measured another car, 2008 Z51 Coupe, totally stock, 50% tread remaining on tires-

Both Front: 26 14/16"

L. Rear: 27 15/16"
R. Rear: 28 2/16"

If we consider the difference in tread depth, that puts him about 2/16" higher than me in front, about the same as me in back.

Gearhead Jim

GM doesn't measure the wheel wells, they measure the distance between two points on the suspension under the car. That requires an alignment rack and a special "Trim Height" gage that not every dealership has or knows how to use. But I bought the gage, both our dealer tech and myself have independantly measured my trim height. According to the 2009 specs, I'm a little low.

Today I dropped my car at the dealer for an oil change and seat "clunk" repair, asked the tech to look up some different years of "Trim Height" specs in his computer; that has the latest from GM. It turns out there have been at least three different sets of trim height specs, which means three different "correct" ride heights, depending on year of production. Since the suspension and body parts are supposedly unchanged on the narrow body cars, that suggests GM simply can't make up their mind. I've posted the 2012 numbers in post #7 edited above, for comparison. The 2012 numbers seem to be a combination of the 2009 front spec and 2006 rear spec.

It's possible that MisterMidlifeCrisis' car looked goofy simply because it was adjusted exactly to the factory specs.

I'm having them raise all four of my bolts by one turn, that should raise my fenders by 2/16" front and 2/16" to 3/16" rear. Of course, it will take another couple of hundred miles of driving for it all to settle out to those numbers.

That will still leave my fenders about 6/16" low in front and 10/16" low in the rear, according to the latest spec. Wow! The factory must be making "Monster Truck" Corvettes.

EDITED TO ADD: I got a brief look at the computer screen, each year had a different page, and it looked like the Trim Height specs for different years were arranged in different ways. It appears that even when GM comes up with a new "correct" trim height, they only publish it for that year, the specs for the previous years remain unchaged even though they are now "wrong".

This does not inspire confidence.

MisterMidlifeCrisis

Well, if my car were set to the 2011 specs, I think it's probably a little high. The Vette is much more stable at high speed and less sensitive to crosswinds with more rake, and under hard acceleration from slow speeds feels less like the nose is rising up. I think it also understeers a hair less with the front lowered a bit more than the rear - it feels like the spring rate is higher but that might be that the center of mass is just lower compared to before.

So, other than more scraping, I've only seen positives from dropping it down from the OEM height, which does really look goofy.

Boomer111

Scraping the air dam is one thing but bottoming out the undercarriage is another.

Just look for the dark spots on the road bed usually this is where the dips are and chance of slamming can occur.

For me I prefer not to tense up at ever dip waiting for the slam. This was the experience with the stock shocks on the 1LT.

Gearhead Jim

Judging from your delivery date and miles, it sounds like you are having a good time with the car, using its full capabilities.
And not afraid to throw the BS flag on some of GM's specs.
Normally, I'm skeptical of people who think they know more than the engineers. But in this case, the big year to year variations in the trim height, make me wonder if the engineers have any clue.

cartop2

2009 coupe, standard suspension and tires, 5000 miles, on level floor after being parked 24 hours.

Front Left 27" Front Right 27 1/8"
Rear Left 28" Rear Right 28 1/8"

Used a tape measure, but I think those are accurate within 1/16"