FORMULA FORD CHALLENGE SERIES

Technical Bulletin

TB: 007

Subject: What Ring & Pinion Gear Does My Car Have?

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Summary:

Determining the ring and pinion gear ration, also known as crown wheel and pinion (CWP), in your Formula Ford’s transaxle is critical to having the proper individual gear ratios for a particular track.

Very early Formula Fords may have an 8:31 CWP (3.875:1 gear ratio), the most common is 9:31 (3.44:1) and later cars or those converted from an F2000 or Formula Continental may have a 10:31 (3.10:1).

The CWP gear ratio is calculated by dividing the number of teeth on the ring (crown) gear by the number of teeth on the pinion gear.

A very commonly asked question is how to determine the CWP ratio in my car.  Here’s how:

Details:

• Remove the rear cover from your Formula Ford’s transaxle.

• Place the gearbox in neutral.

• Raise only one wheel in the air.  The other should still be on the ground or immobile.

• Place marks on the tire and pinion shaft nut and turn the free wheel exactly one turn.  The pinion shaft will turn:

  •   Almost 4 times (3.875) if you have an 8:31;

  •  Just under 3 ½ turns (3.44) if you have a 9:31;

  •  Just over 3 turns (3.10) if you have a 10:31.

Alternately if you cannot decern the slight differences in turns, for more accuracy:

• Turn the pinion (upper) shaft of the gearbox 15 ½ turns.

• The one free tire will rotate 8, 9 or 10 times; corresponding to an 8:31, 9;31 or 10;31 CWP.

• It is easy to lose track of the number of wheel rotation, so if you can, have someone count the wheel rotations while you turn and count the pinion shaft rotations.

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