Racing Tire Durometer

PTC has announced Model 306RL, the durometer specifically tailored to measuring racing tire hardness.  The Model 306RL durometer is the first choice for use by tire manufacturers, technical inspectors, race teams, and engineers fast and accurate tire hardness.  Used to determine conformance to durometer rules, class rules and the tire manufacturers specifications. The Model 306RL is also a great tool for spotting chemically softened tires.

The Model 306RL Durometer accurately and easily measures racing tire hardness in compliance with ASTM D2240 (Type A). The large rectangular base ( 1”x1.5”) is ideally suited to obtaining repeatable readings on tires. The durometer features a low glare dial,  bold easy to read numbers and a bright red paint job making it easy to locate. The durometer comes standard with a Max Hold hand, which retains the peak reading for easy reading. The top knob permits both hand held use and attachment the accessory Model 441 1kg Constant Load Deadweight. The Model 441 provides more consistent measurements by providing the downward force. Each instrument is individually calibrated using standards traceable to NIST. A test block and sturdy carrying case are included with the durometer as well as a nylon belt pouch.  Accredited certification is optional.

Model 306RL Type A
Racing Tire Durometer

Download Operating Instructions

Tech Tips

The standard hardness scale for rubber racing tires is Type A ASTM D2240.   The Type A scale reads from 0 to 100 durometer points.  A typical short track asphalt tire will read in the 70’s for example.  A correctly calibrated durometer will read to ± 1 point.  The hardness of the rubber will vary over the tire’s surface. 

Measuring Tire Hardness

To use a durometer to measure the hardness of a tire, PTC recommends the following procedure. Use a durometer with a rectangular base approximately (1 x 1.5 inches) such as PTC Model 306RL. 

• Set the memory hand to below 20.
• Place the short axis of the durometer base on the tire aligning the long axis with the direction of travel.  • Tilt the base up about 30 degrees resting on short axis.
• Gently roll the base of the durometer on the tire exerting approximate 2.5 pounds of downward force, until the durometer is tilted 30 degrees in the opposite direction.    This motion should take a little over a second to complete. 
• The tire hardness may now be read from the memory hand.  Be smooth and do not rush to obtain accurate and repeatable readings.
• For best results take 3-5 tests at least 1/4” (6 mm) apart and use the average value.

•Record the hardness and temperature for future reference. Readings are normally taken from 70-77 degrees Fahrenheit, a surface thermometer such as our Model 315F, can be used to measure the tire’s temperature.