Mk III-T Concept and Design

I. Goals

III-T was to be as light as reasonable achievable, with a target of at least 100 lb. lighter than II, specifically less than 1000lb. with driver. This had to be accomplished using easily available materials and construction techniques, i.e. steel tubing space frame, aluminum sheet reinforcement, light fiberglass bodywork, light powerplant, and as much aluminum in suspension components as could reasonably be accomplished.

The driver containment cage was to be of .080 alloy tubing, 4130 steel, 1 3/8” diameter, remainder of the chassis 1025 steel square and rectangular tubing. Tubular structure would be minimal, with bending and torsional strength added by structurally stressed sidepods of triangular cross-section with internal ribs, such as are used in construction of airplane wings.

The engine would be turbocharged, initially of 580cc, later enlarged to 620cc by rule change, based on Honda V4 motorcycle engine, specifically VF-700F2 Interceptor, originally of 700cc. displacement.

Bodywork would be fiberglass, in several sections to ease assembling by one person. Carbon fiber was attractive, but prohibitively expensive.

II. Concept Details

Chassis would be narrow, single-seat design, allowing maximum length of suspension links for optimum geometry; front lower links could essentially have inner pickups at chassis centerline.

Front track would be quite wide, 60” or so, with rear track quite narrow, around 52”. Since no differential was contemplated, corner-entry understeer would thus be minimized.

Front suspension would utilize monoshock concept, using a central rocker, to eliminate the weight of one coilover unit.

Rear suspension would be conventional, again maximizing length of links.

Engine bay would be simple framework, using the engine as a stressed member.

Front uprights would be fabricated, using contained stub-axles and internal bearings; an aluminum midget steering rack with titanium extensions and aluminum tubing steering links reduced front-end mass, with aluminum two-piston brake calipers and aluminum rotor hats to further reduce unsprung and rotating mass.

Aluminum wheels, 13” X 6” front and 13” X 8” rear would allow use of commonly available race tires from several manufacturers.

Zonker Mk III-T would weigh around 750lb. without driver, the engine would produce about 190hp, and thus it was felt the concept should have reasonable performance.