V1.3 Oct 27 2008

The intent of this work is to share all the lessions I learned during my racing career; dumping as much of my brain and hard-earned knowledge into the public record as I can. It is, however, NOT public domain. I reserve the copyright for myself. You may NOT duplicate this elsewhere - including linking images - without my express permission - and this is the age of Google, folks, I WILL find you if you post it elsewhere. Otherwise, read and enjoy, and put this all to good use. Go fast!. DG

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.

It's more than a little bit ugly, but most of what you need is there.

The remaining work on it is to provide a data entry block for your own shocks (to compare against the theoretical ideal and to do mouseover tooltips to help explain what each parameter is. That may or may not happen in the near future.

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.

A somewhat odd complaint arose about this calculator... that apparently I'm making all this stuff up.

Well... one should cite one's sources, I guess. All the math comes primarily from:

	Competition Car Suspension by Allan Staniforth Fourth edition, largely updated book on the design, construction, and tuning of race car suspensions. An easier way into the material covered in Miliken. Buy this one first to get the basics, then dive into the Miliken book.
	Race Car Vehicle Dynamics by William F. Milliken This is the definitive reference textbook on vehicle dynamics. Not for the beginner! More calculus and other math than you can shake a stick at, and somewhat disorganized, but this book contains every racing/handling concept, formula, and model yet published. If you don't own this book, then you're not serious about your engineering.
	How to Make Your Car Handle by Fred Puhn The classic "generalist" handling book. Slightly dated, but otherwise an exhaustive treatment of handling and how to improve it, mostly from a modification of an existing car standpoint. A good first book. Also contains a procedure for measuring CG height. (Page 159)
	Race Car Engineering and Mechanics by Paul Van Valkenburgh A good summary of race car engineering issues. Paul writes for Racecar Engineering and is a true scientist. Lots of good stuff in here. Also contains a method for measuring CG height (pp 131-132)
	Chassis Engineering by Herb Adams (of Trans Am fame) Another general "handling" book, but Herb goes into quite a bit more detail on chassis rigidity, and how to build rigid chassis, than the typical generalist. Good reading before you build your roll cage, and especially good for tube-chassis classes like CP. Some discussion (and formulas) for spring rates, wheel rates, and instant centres.
These you can't buy from Amazon. The first is my certificate from attending Claude Rouelle's Racing Engineering Seminar in which he covers everything discussed in the calculator. The second is my copy of Carroll Smith's Engineer in a Pocket that I had him autograph after he finished consulting on my car (just before he passed on). I got the "measure and model" religion direct from him, when he more or less called me an idiot for not having done it yet (and he was absolutely right)

There's more at our Amazon Store

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:

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Power | Required Reading and Cool Stuff

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J. Toby Markoff, eat a dick.