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914World.com _ The Paddock _ Center of gravity for my 914

Posted by: groot May 20 2006, 01:46 PM

I've been told the Cg for a 914 is around 16", but this seems high to me, since the pwertrain is so low in the vehicle. I finally got around to measuring it, albeit, somewhat inaccurately.

So, I borrowed some scales, weighed the car, raised one end 10" and weighed it again. This moved 20 pounds.... So, by my crude calculations and crude measurement that puts my Cg at 9.6 inches.

Consisdering how low I run the car, seems pretty close to me. The middle of the engine sits at abou 10 inches.

Has anyone else measured their Cg???? I'd like to get some confidence in my numbers.

Posted by: J P Stein May 21 2006, 07:14 PM

How are you calculating that?
The race car calculation book is checked out of the library this week.

Posted by: groot May 22 2006, 05:20 AM

Just a bit of vector geometry.... but Longacre has a quick and dirty version in their instructions that come with their scales.

The accuracy goes up with the height you raise the one end, but I had trouble getting it 10" high.

Posted by: Brett W Jul 7 2006, 02:07 AM

is this with you in the car? I feel it would change if you are in the car. The 16 inches does seem high, but that was from you know who.

Posted by: Borderline Jul 8 2006, 08:39 PM

I haven't gotten around to doing it yet, but thanks for the opportunity to study the math. I think I would need the before and after weights to be more accurate. Assuming a 2000# car with 1000# front and rear to begin with and ending with 1020 rear and 980 front that would shift the cg back about .86". The car raised 10' in the front creates a 5.95 degree angle. My calculator says the cg is about 8.25" above ground level. It's been a long time and right now I'm not sure if the original location of the cg is important. I always thought the cg was pretty close to the centerline of the wheels and and engine. give me the raw data and i'll give it another try

Posted by: groot Jul 10 2006, 06:36 AM

Me in the car... I don't have the numbers here, but the math does work out.

Posted by: Brett W Jul 12 2006, 01:53 AM

The majority of the weight in a production car will be in the crank case and tranny. You can't get the engine any lower than the axle centerlines so that right there will put the a lot of the weight up high.

Now with you in teh drivers seat and a full tank of gas that will alter the CG slightly, but I doubt it is enough to over come the 200lbs at the axle centerline. If I had a complete car I would put it on the lift and measure it, but all of my cars are in different states of dis-assembly.

Posted by: groot Jul 12 2006, 11:32 AM

I hear ya, Brett, and I agree with you. A good portion of the powertrain is below the axle and the axles sit at 11.25" from the ground. My 200 pound ass sits about 4 or 5" off the ground as does the fuel tank.

From these rough measurements, 10" seems in the ballpark.

Posted by: Brett W Jul 12 2006, 03:11 PM

Good point. I forget you are running a 22.5in tall tire. DOH, yeah the axle centerline is not where it used to be. Your numbers actually sound very reasonable now.