IRHD (International Rubber Hardness Degrees) provides the standardised measurement scale for tyre compound hardness, with lower numbers indicating softer compounds that provide increased grip but faster wear rates, whilst higher numbers denote harder compounds offering durability at the expense of ultimate grip.
IRHD scale interpretation:
- Soft compounds (30-40 IRHD): Maximum grip, rapid wear, best for qualifying or short races
- Medium compounds (40-50 IRHD): Balanced performance and durability for most race conditions
- Hard compounds (50-60 IRHD): Extended life, lower grip, suited to endurance racing or abrasive surfaces
Tyre manufacturers specify IRHD ratings for their compounds, allowing drivers to select appropriate tyres for expected conditions and race strategy. Soft compounds generate heat quickly and work well in cold conditions or on green tracks, whilst harder compounds suit hot weather and high-grip rubbered surfaces where softer tyres might overheat or grain. Track temperature significantly affects optimal compound choice, as a soft tyre perfect for morning practice might prove too soft for afternoon racing as temperatures rise. Understanding IRHD ratings helps teams make informed tyre choices, balancing qualifying pace against race durability to optimise overall event performance.