Audi's square front tires have helped to compensate for power reduction in the 2011 Le Mans regulations. Photo credit: Rick Dole for Michelin North America

Michelin: It’s Hip to Be Square (and Quick) at Le Mans

As it seeks an unprecedented 14^th consecutive overall race win in the prestigious 24 Hours of Le Mans race, Michelin has introduced a new weapon: “square” tires.

Tires are round and Michelin tires are known for their quality and consistency from set to set, but the buzz here at the 2011 running of the prestigious 24 Hours Le Mans is about the Michelin “square” tires.

“What everyone is talking about is what we call a “square” fitment,” said Karl Koenigstein, Michelin American Le Mans Series technical team leader. “Rather than running narrow tires on the front and wide tires on the rear of the car, we have virtually the same size tires on all four corners on several of the top cars.”

The latest 2011 Audi, Peugeot, Aston Martin and Lola Toyota prototypes are all designed to race at Le Mans with near maximum width and diameter Michelin tires on the front as well as the rear wheel positions.  During Le Mans qualifying, the top six cars were all Michelin wide tired prototypes from Audi and Peugeot.

The wide tire is in the front and the traditional in back. Photo credit: Rick Dole for Michelin North America

Old or New?

Actually most passenger cars today come with a square fitment. Even in racing, a square fitment is an old approach, but with the decades long emphasis on aerodynamics at all costs, teams wanted narrower front tires to reduce drag.  The last “square” fitment to win overall honors at Le Mans may have been a Ferrari nearly 50 years ago.  More recently Acura ran a square fitment in the American Le Mans Series in 2009 with the Highcroft and de Ferran LMP1 teams. 

New 2011 rules for the 24 Hours of Le Mans and the Intercontinental Le Mans Cup have reduced power, especially torque, so teams want to carry as much momentum as possible through the corners and that places the premium on maximizing mechanical grip.

“Michelin technical partner teams running the square fitments can take advantage of the increased volume in of two ways,” said Koenigstein. “Teams can use softer compound tires as there is more rubber volume to absorb the energy, or they can take the benefit in extended wear with our standard compounds.”

“The cars, especially the diesels like Audi and Peugeot, do not have the big torque to launch the cars off the slower speed corners they have had in the past, so they want to achieve the lap time in a different way,” said Koenigstein.

To accommodate the wider front tires while minimizing the aerodynamic losses, teams have worked to design narrower center sections of the front and reengineered steering and suspension attachments.

“The taller tire also increases load capacity,” said Koenigstein.

Peugeot's set of wider front tires in comparison to a regular set for prototypes. Photo credit: Rick Dole for Michelin North America

Why Square?

According to Michelin, there are three main advantages to the wide front or “square” fitment approach: 

• The overall tire contact patch is increased by about seven percent ,
• The total volume of rubber (width and diameter) is increased by approximately 17 percent.
• The greater contact patch and tire volume help to provide better braking and corner entry speed.

“The larger contact patch means more tire on the road and that certainly helps cornering and braking,” said Koenigstein.  “You have a wider front tire to spread the load around which helps, but you are braking later and carrying more speed into the corner.  You are really working the front tires much harder than before.”

To turn quick lap times around the 8.462 mile circuit at Le Mans, drivers will need to hustle the car to carry more speed into the corners. With less acceleration off the corners, traffic becomes a more difficult proposition. As a result, teams anticipate a bigger spread between a car’s best laps and its slowest laps.

Moving offline to pass on the outside of the corner carries some risk of picking up debris from the accumulated rubber marbles, stones or shards of carbon fiber bodywork. It can also take drivers a bit longer to build up tire temperatures and pressures with the wider front tires.