Wheelbase & Tracks

Wheelbase and tracks are the first parameters to be set because they determine the total packaging constraints.

Things to consider when choosing a wheelbase and track;

·         Lateral weight transfer

·         Longitudinal weight transfer

·         Yaw moment of inertia

·         Aerodynamics

·         Packaging

·         Type of car

·         Type of race track

·         Rules

Weight transfer

Total weight transfer (i.e. geometric + elastic weight transfer) is a function of track width (lateral) and wheelbase length (longitudinal). A wide track will cause less lateral weight transfer during cornering. A long wheelbase will cause less longitudinal weight transfer in braking and accelerating.

Weight transfer is undesirable because of tire load sensitivity. Tire load sensitivity is the falling rate of its lateral or longitudinal grip when placed under an increasing vertical load for a given slip angle. This means that as the vertical load on a tire increases it’s lateral and longitudinal grip increase by a smaller gradient.

Yaw Moment of Inertia

An increase in track or wheelbase will cause the masses of the non-suspended components (e.g. rim, tire, hub, upright, brake etc.) to be placed further from the centre of gravity of the car. This will increase the cars yaw moment of inertia.

A cars ideal yaw moment of inertia is a compromise between “stability” and “response”. The best compromise between stability and response depends on the circuit the car is racing on.

Type of Situation	Best Configuration	Comments
Fast/Large radius sweepers	Long Wheelbase Wide Track	Stable platform Less weight transfer
Tight hairpins, Chicanes or Slaloms	Small wheelbase Track as large as possible (rules, circuit etc.)	Unstable platform Good transient response
Circuits with very long straights	Long wheelbase	Added stability for aerodynamic and road disturbances at high speed. Increased braking performance

Aerodynamics

The frontal area of the car will be affected by the chosen track width. An increase in track width will cause an increase in drag. Track changes in open wheel race cars will affect the entire flow pattern of the car.

Packaging

Clearance between wings, end plates and wheel arches will influence wheelbase and track dimensions.

Half Track Variations

The half track will change as the suspension articulates. How much it changes will depend on the suspension’s geometry. As the half track changes during a motion the tire is forced to move laterally. If the half track changes a by a large amount the tire will slide across the road surface. This will lead to increased tire temperature and premature tire wear.

Wheelbase Variations

Excessive wheelbase changes during the roll, pitch and heave motions can cause irregular handling behavior. Wheelbase variations are caused by suspension geometry that causes the wheels to move forward or backward as the suspension articulates.