Instant center
11-23-2010, 08:48 AM
#61
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Thanks. Great explaination. We have the fore and aft CG fiqured out by weighing it on a scale. I'll get my string out and check this out.I did this on Sunday and figured out our IC on the car. The IC is forward of the CG and about the height of the door sill. On Measuring for the PR one paper I read stated that you ran your line from the tire contact point to the center line of the front wheel and tire. The other never said what to reference the line to. Your answer makes more sense. I'm just trying to learn why the car reacts like it does. We are making good power just trying to hook it up with the parts that we have. Thanks again. Now for a shock class. LOL
11-23-2010, 10:06 AM
#62
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Glad to help... there's a obvious need for some clarity on these issues. So, the paper you reference was likely referring to the "neutral" or "anti-squat" line, another valuable line to plot on your drawing. The neutral or anti-squat line runs from the rear tire contact point through a point defined by the CG height and the front axle centerline. cars with ICs below this line (<100% Anti-squat) tend not to separate the chassis, and the opposite is true for ICs above this line. Remember, the amount of torque applied to the tires/starting line ratio and the magnitude of your polar moment of inertia have a huge impact on the quality of your launch as well. Making this drawing as you are, is the necessary start. Shocks will give you some fine-tuning ability to control the launch behavior, but the foundation for understanding launch behavior is the chassis scaling you're doing.
Bob (Plumbbob on TNfbody.com)
P.S: CG determination using camshaft height IS an approximation, and is fine for tuning your car. Percentage of rise/Anti-squat values and launch behaviors really can't be transferred or expected to be functional on another car, unless that car is IDENTICAL. (extremely unlikely) Chassis tuning and scaling relative to camshaft height CGs is fine for single platforms. Chassis shops will want to use the empirical CG height determination method to transfer tuning combinations from car to car. Brush up on your trig!
Bob (Plumbbob on TNfbody.com)
P.S: CG determination using camshaft height IS an approximation, and is fine for tuning your car. Percentage of rise/Anti-squat values and launch behaviors really can't be transferred or expected to be functional on another car, unless that car is IDENTICAL. (extremely unlikely) Chassis tuning and scaling relative to camshaft height CGs is fine for single platforms. Chassis shops will want to use the empirical CG height determination method to transfer tuning combinations from car to car. Brush up on your trig!
11-23-2010, 01:57 PM
#63
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Yes thats correct. I was getting them confused. I was thinking they were the same measurement. Thanks again. Most of these figures are fixed and can't be changed or not much with a stock type chassis is what I'm finding.
