Cooper Tires: Rallycross Innovators

From a distance, the tires on the Americas Rallycross (ARX) cars may look like any other but get a closer look and you’ll see that the Cooper Tires used on these extreme dual-surface, four-wheel-drive monsters are designed especially for a purpose.

A rallycross tire has to cope with a unique set of circumstances during the intensity of a rallycross race. With tire warmers not allowed, the four tires have to work from cold temperatures when 600 bhp gets put onto the ground by the ARX Supercars. They then have to cope with both asphalt and dirt in just one lap, which also includes impacts from jumps, curbs and the sideways forces of sliding with the wheels spinning at high speed.

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ARX tires are provided exclusively by single-supplier Cooper Tires, a brand that has a long and successful history in rallycross as the tire of choice in rallycross events around the world for over twenty years, dominating the FIA European Rallycross Championship before it became the sole supplier to the FIA World Rallycross Championship for 2014.

Cooper Tires use a pattern that conforms to the technical regulations with a compound suitable for both dirt and asphalt surfaces. It needs a complex construction that gives unrivaled performance but with the strength to take the punishment of a rallycross race.

The unique construction allows the tires to perform predictably at much higher slip angles than would be possible with typical World Rally Championship products. The graph below shows that cornering force vs slip angle, at 2 degrees negative camber, continues to increase well beyond the +/-7 degrees of slip angle measured on the force moment rig. Normally this graph would plateau at 4 or 5 degrees. This allows the cars to race in close proximity, with the drivers having the confidence to accurately position them, even when travelling with spectacular angles of drift. It is the result of 20 years of open competition and collaboration with the best Nordic drivers, European factory teams, and British design engineering from a specialist race tire manufacturing facility.

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The hand-built Cooper Tires have been tested and developed to operate in a wide range of temperatures and conditions. Typically, a rallycross compound will work at 194°F, but will comfortably go up to 248°F in hotter conditions or on tracks that are mostly paved.

All homologated rallycross tires must feature a ‘tread’ pattern that complies with a specific set of regulations as approved by the FIA. Cooper’s ACB11 Rallycross tire was developed from a range of rallycross slick tires to conform to these regulations which state that between 17% and 25% of the tire must be a pattern or ‘void’; this is often referred to as the ‘land to sea ratio’. 

Each ARX competitor can use twelve new dry and wet tires at each round, choosing when to use fresh rubber a critical tactic in challenging for qualifying and finals victories.

Check out who uses their eight allocated tires best at next weekend's Grand Prix de Trois Rivieres, August 4-5. To catch some of the most exciting racing in the world, purchase your tickets now to World RX USA, held at Circuit of The Americas, September 29-30. Go to https://www.worldrxusa.com/tickets to purchase your tickets today.

 

Tiernay Oliver