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Part I - Designing a Stadium Lite that works

There are basically four chassis in the race world; the Pilot, the Generation III Briggs Built, the nine year old design Triple E Stadium Car that Joe Price drives and the other is the Briggs Built Generation IV - of which only six exist, four of them are in short course form and the other two are long course cars. There are a handful of home built cars out there too. A couple of them work very well, I might add.

During the season I was able to study both the Triple E and Briggs Generation IV cars quite a bit. Much of the Triple E is actually quite similar to the Pilot in layout. The length of the a-arms and width of the chassis are close, but the weight bias it quite different. The Briggs Built is an entirely different beast. It has very long a-arms and rear links. It has a weight distribution of approximately 50/50 front to rear (compared to the Pilot's 35/65 front/rear ratio) and a very narrow chassis where the suspension components attach. This car flat screams compared to the majority of the Lites out there. Bob Briggs took a lot of time, effort and testing getting it right.

Front Suspension Movement TrackingBy making the suspension arms and links as long as possible the chassis is less upset by input from the wheels and the angles which the suspension components travel through are drastically less. This is easier on components such as ball joints and heim links and CV joints than high angle changing suspensions. Also, the travel of the suspension can be increased on a long travel car allowing for more sag to be built in, thus lowering the center of gravity (CG) of the car. The lower the CG, the better the cornering becomes. Another nice thing about having very long swinging parts is that the overall width of the car changes less as it goes through it's travel. A car like a Briggs Built Generation IV may only change one to two inches in width in a thirteen inch travel range while the Pilot may change as much as two to three inches in eleven inches of travel. The whole key is that the car goes through less changes as it goes through it's suspension travel range.

After talking to a number of people that have designed parts for both full sized cars and Stadium Lites, I started working on the front spindles first. These are responsible for the way the car steers. Some of the terminology that applies to the front end of the car is:

Kingpin Angle & DesignCamber - the amount the wheels are angled from vertical while facing the front of the vehicle. In other words, how much the top of the tires lean in towards or out from the body of the car.

Caster - the amount the front spindles are angled from vertical forwards or backwards while facing the front of the vehicle. Think of this term as "casting" a fishing pole.

Toe - in, out or zero. This is a measurement of how parallel the front wheels are to each other.

King Pin Angle - this is the angle from vertical of the upper and lower mounting points of the suspension through the spindle. This it the blue line in the diagram at the right.

Inclined Angle - the relationship between the angle of the king pin angle and the axle.

Scrub Radius - Imagine that the wheel in the diagram on the right was to pivot (steer) right in the middle of the tire where it rests on the ground. The scrub radius would be 0 degrees. Notice that the king pin angle meets the ground just to the right of the center of the tire. This difference is called the scrub radius. Basically, the amount of offset the tire swings around its pivot axis as it is steered.

Contact Patch - where the tire and the ground come in contact.

By adjusting the camber, caster, king pin angle and inclined angles the placement of the contact patch is decided. As the tire rotates through its steering, the contact patch can me set up to move front to back and/or side to side. By moving this contact patch as the tire steers, grip can be developed or lost. I'm the first one to admit, I'm going off of some settings that I was told works well for the Lites. I'm going to start out with a king pin angle of 5 degrees This will give me a scrub radius of 1-7/8 inches. I will be able to change these angles a bit if needed.

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6/4/01