Center of Gravity in Relation to Instant Center - '09 GT500

[Scott8]

Does anyone have a reference to find the center of gravity for the '09 GT500s? After measuring the contact points for the rear suspension, it looks like my instant center is 84" in front of the front tire (I have 20" staggered rims - so the slope of my LCAs is surprisingly negative). I purchased Maximum Motorsports LCA relocation brackets and noticed they have three settings. The lowest drops the arms by 3.875", which will bring the instant center behind the front wheels and much closer to the neutral line.

The problem is I can only guess the neutral line. I don't have four scales to weigh the corners to calculate the center of gravity - so I just guessed by measuring the top of the waterpump (24" high) and my clutch (89" in front of my rear axle).

I'm going after good handling - not hard launches - so I don't want the anti-squat to be over 100%. However, if I'm wrong on the estimated center of gravity, my neutral pitch line will be wrong and my anti-squat ratio will be incorrect.

Obviously, any reference out there would be for stock. I can adjust from that. The only Mods I have that weigh anything are larger/lighter wheels, BMR subframe connectors, and Shelby rear strut tower brace.

Below is the graph after measurements. The green line is the only estimation.

 

[SteveWK]

I'm sure you can find a race shop that has scales and they could weigh all four corners for a small fee, but all that would tell you is how far back/front and left/right your c.g. is relative to what ever point you are using as (0,0). It wouldn't tell you how high it is relative to that plane. I did a google search on "finding car cg" and lots of information is out there. One site shows how to find the height also, but it is a rather involved process. Here is the site if you are interested http://www.thecartech.com/subjects/auto_eng/Center_of_Gravity.htm . There are others showing basically the same method. I like what you are doing. I'd like to do the same, and simulate it with some of the suspension software out there, but haven't got around to it.

 

[Scott8]

Thanks. Measuring was a fun, quick way to get the teens out in the garage. Then my daughter showed me the website she uses for graphing homework (Desmos | Graphing Calculator). The whole process took just a few minutes.

I will be looking for a place with scales to finish it up. Thanks for the resource.

 

[Black Cobra '99]

Maximum motorsport provides a rough calculation for anti-squat geometry in their installation manual. For handling, you want the highest hole and depending on your ride hight I think anti-squat should be around %50.
When it comes to finding cg, there is no easy way, either estimation or find a scale. Unless you are tracking your car competitively and looking for tenths of seconds, a couple percent on anti-squat wouldn't do much, heck I doubt you'll feel anything on the street if you change from highest to lowest hole.

 

[802gt500]

On the street with 555r and changing holes made big traction differences for me. Found 1 hole down from stock works well. The bottom hole i did not have enough traction to plant the tires