Suspension Dynamics Calculator

OK, here is the motherload.

This is a web-based version (slightly simplified) of the Excel spreadsheet I designed and used to work out all the various calculations needed to properly set up the car.

Yes, the graphs don't work in Internet Explorer (download Firefox already, all four of you who still use IE!)

The remaining work on it is to provide a data entry block for your own shocks (to compare against the theoretical ideal)

The key to using this application is Accurate Measurement. There's a lot of data you have to pull off the car and accuracy counts!

Remember: Garbage In, Garbage Out!

Some of the data is fairly simple to collect (like corner weights). Others, (like CG height and roll centre height) take a little more work.

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The Calculator

Inputs

Corner WeightsPounds From your scales, with driver and average fuel load. Don't forget to disconnect the sway bars! Left Front Right Front Left Rear Right Rear	Unsprung WeightsPounds Best to weigh these directly with the sprung weight supported on jackstands. Really don't forget to disconnect the swaybars! Front Rear	Chassis Spring RatesPounds per Inch Hypercoils you can trust. Everybody else gets the spring rate tester. Front Rear	Tire Spring RatesPounds per Inch This you must measure directly. Tire pressure counts! Front Rear
Motion RatiosDimentionless, 2 decimal places Get this from WinGeo, and measure directly with a pair of dial indicators and some imagination as a sanity check. Note this is a curve, so measure at static ride height. This calculator assumes coilovers, so if your springs and shocks are not coaxial (Mustangs) you're SOL for the moment. Front Rear	Design FrequencyHertz This is a "magic number", in that it cannot be derived. Somewhere betwen 1.8 and 3.0 is usually right, with the rear being 0.2 Hz higher. Front Rear	Design Damping RatioDimentionless, to 2 decimal places Almost always 0.65 Front Rear	Digression KneeInches per Second Shock speed above which you want the curve to digress. Needs to be faster than the fastest shock speed due to chassis movement. 3 in/sec is usually OK. Ratio is slope of curve post-digression. 0.15 is OK Velocity Ratio
Chassis CG HeightInches This is a rough one to get... more to follow   Front Rear TrackInches From WinGeo Roll Centre HeightInches From WinGeo Axle HeightInches From WinGeo	Anti Roll Bars   Front Rear DiameterInches Super sensitive! Use a micrometer, and chip off powder coat! LengthInches The length of the straight portion of the bar Arm LengthInches The length along the bar from the straight section to the endlink attachment. Arm HeightInches The distance from the straight portion of the bar to the endlink attachment, measured at 90 degrees to the straight section. If your arms are at 90 degrees (real race cars, not most street cars) this is the same as Arm Length Motion RatioDimentionless From WinGeo

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Results

Sprung Weights   Left Right Front Rear	Wheel Rates Front Rear	Ride Rates Front Rear	Natural Frequencies   Left Right Mean Front Rear	Ideal Spring Rates   Left Right Mean Front Rear
Roll Resistance at 1G   Front Rear Springs Bars Combined Distribution	Weight Transfer   Front Rear Total Unsprung Via Roll Centres Via Springs & Bars Totals Distribution		Resulants Roll Moment Roll Angle (1G)	Understeer/Oversteer
Front Shock Curves Forces at 1 in/sec Bump: Rebound:
Rear Shock Curves Forces at 1 in/sec Bump: Rebound:

J. Toby Markoff, eat a dick.

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