Interview with AimÃ© Chatard (Michelin): High heels on ice. On the icy stages of the Swedish Rally, the 307 WRCs will resemble giant grasshoppers sitting on skinny bicycle wheels. Michelin Competition's Rallies Manager AimÃ© Chatard explains the...
Interview with Aimé Chatard (Michelin): High heels on ice.
On the icy stages of the Swedish Rally, the 307 WRCs will resemble giant grasshoppers sitting on skinny bicycle wheels. Michelin Competition's Rallies Manager Aimé Chatard explains the reason for this bizarre metamorphosis.
How is it possible for the power of today's World Rally Cars to pass via such a small amount of rubber?
"On ice, you could say that the rubber tread blocks simply serve to hold in place the studs which are entrusted with the job of ensuring grip and transmitting the car's power to the ground. To do this, you need as much pressure on the contact patch as possible and a narrow tyre allows the studs to bite firmly into the ice. A small contact patch also ensures better clearance of the particles of ice and/or snow that can otherwise detract from the tyre's potential. On such narrow wheels, modern WRC cars effectively look quite awkward but this is really what makes them so potent."
This impression is accentuated by the fact that the sidewalls of these tyres seem higher than usual.
"That's true to an extent, but an optical illusion does make the sidewalls appear higher than they actually are. The regulations specify a maximum exterior diameter for all WRC tyres, whether they are fitted on 18" asphalt wheels or on the 15" rims used on gravel. The 16" rims used for the ice and snow in Sweden effectively produce a relatively tall sidewall dimension, and that's a positive feature in itself, but they also enable bigger brakes to be fitted and that can also come in useful. Indeed, the braking power, traction and grip of a studded tyre are superior to that of their gravel equivalent. Yet the 380-odd studs permitted by the regulations - that's around one stud per square centimetre - do not actually come into contact with the ground that much. When the car is running at top speed, only four studs are actually doing their job fully."
How do you explain this extraordinary grip?
"The way the studs work is based on the same principle as an ice axe. They only bite into a very small surface but they anchor themselves in. Ideally, the phenomenon of sliding would be zero. However, at temperatures of 20°C or less, ice is as hard as concrete and a very strong stud is required to bite into it if you don't want to run the risk of it wearing out too quickly. On the other hand, as you get closer to 0°C, the ice becomes more brittle and this can result in sliding and the beginning of wheelspin, two phenomena that increase the constraints to which the fixation of the stud inside the tread block is subjected. To be capable of standing up to the forces in play, we employ different metal alloys according to the different types of punishment faced by the studs. The design of the studs themselves can also vary according to the job in hand."
If the stud is so important, does that mean the tyres themselves are just accessories?
"The notion that the tread blocks only serve to hold the studs in place is in fact oversimplifying the picture. The regulations specify a maximum number of studs, as well as their weight, length and diameter of their base. This means that the bonding power of the glue we use to fix them in the rubber is extremely important and this process calls for specific, reasonably complex production techniques."
Interview with Corrado Provera: A promising start
The 307 WRC rose to the occasion of its maiden appearance in world class rallying by recording three fastest stage times in Monte Carlo and coming away with nine championship points, encouraging confidence boosters for Corrado Provera and his troops.
The decision to run the 307 WRC on the Monte Carlo Rally was apparently a good one.
"The whole team did a fantastic job in complying with the timeframe and ensuring we had a competitive car in Monte Carlo. To get both 307 WRCs to the finish and the fact that we came away with more points from this event than ever before is a fantastic and fitting reward for everyone at Peugeot Sport."
Marcus is always quick on the Swedish Rally, an event on which Peugeot is unbeaten. Do you think the 307 WRC can take its maiden win there?
"Our pre-Swedish testing was very positive and Marcus now knows that the car is competitive and apparently reliable. But we mustn't take anything for granted and we go to Sweden in all due humility."