CLASS FB AND F2 TIRE REGULATIONS

Background Information

TOP

In 1969 both the SCCA GCR and the FIA Rules addressed wheels and tires on Formula B and Formula 2 cars as open...no limitations or restrictions.

As a practical matter the size of the tire was determined by market availability of suitable tires. In the U.S. Formula B cars ran almost exclusively on Firestones and Goodyears.

Neither Goodyear nor Firestone manufacture tires today that would match 1969 tires. This essentially leaves Dunlop and Avon as suppliers.

The tread width aspect ratio is important for at least four reasons: (Tread width aspect ratio is the ratio of the section height to the tread width.)

1. To preserve the vintage look of the cars in our series. Low, wide tires look contemporary.
2. In 1969 the English and European designers tended to run tall tires on wide wheels with narrow treads in search of tread stability.
3. Modern tires tend to have more perpendicular sidewalls; the difference between the sidewall, or section width, and the tread width, is not as great.
4. Tread width is the major factor affecting relative performance in a racing tire. The section width aspect ratio used in the passenger car tire industry generally describes the width of the body of the tire - which is important when you are dealing with body work clearance and ride height.

Tire height: the cars we are concerned with are pre-1970, or cars up to 1972 which are prepared to 1969 standards. If the suspension pickup points and geometry are original, most of them will require tires of 22" to 23" in order to maintain reasonable ride heights and roll centers. If a 1969 car works well with 19.5" front tires, it is likely the suspension has been seriously redesigned.

*In the last year hand grooved Avons have appeared with a very aggressive tread pattern with fewer grooves around the circumference of the tire than anything seen in the late 60"s. After much consideration and with helpful input from Bob Woodman and Charlie Gibson the following tire specifications have been adopted for 1999

1. Groove width 1/8" - 5/32"
2. Groove depth must equal the depth of the moulded tread wear indicators.
3. Cars must have a minimum of 2/32" tread depth to start a race.
4. Tread pattern repeat cycle must measure 1 1/8" to 2 1/4" from block to block.
(Block consists of two angled grooves)
5. Side cuts must meet at an imaginary line (generally 1/4" to 1/2" long)
6. Shoulder cuts will run to the edge of the tire tread
7. The circumferential grooves must be equally spaced across the tire tread surface.

Tires not on this list, or newly introduced tires, may be accepted upon approval of the MR Board. Tread patterns must be as supplied by the manufacturer, and sultable for all-weather use. Rain tires are not acceptable. Additional handcutting or grooving is not allowed. Recap tires are not allowed. Avon tires must be A 11 compound or harder.

Class FB & F2 cars must have a minimum front tire diameter of 21 inches and minimum rear tire diameter of 22.8 inches.