F1 tyre tech analysis: camber, pressures and why reverse tyres?
|By Craig Scarborough||Thursday, July 4th 2013, 11:55 GMT|
Pirelli's post-British Grand Prix analysis identified several factors that contributed to its tyre failures - reversing tyres, low pressures and extreme camber angles.
AUTOSPORT's technical writer Craig Scarborough explains all.
Reversing tyres - running them on the opposite side to the one they are designed for - is not a new trick but has come and gone with different tyre suppliers.
Pirelli tyres are asymmetric, requiring the outer face of the tyre is mounted on the outer face of the wheel, but they are not strictly directional, meaning that a reversed tyre will work.
It is common practice for teams to reverse a worn set of tyres and the outer shoulder of the tyre is still the outer shoulder when reversed and there does not appear to be a performance advantage.
Instead, it is about teams aiming to get more use from worn sets because tyres on one side of the car will wear more the other.
Because of the asymmetric design of the steel belt in the pre-Nurburgring tyres, there is the problem that a reversed tyre has the joint between its two ends pointing in the opposite direction, making it easier for it to separate if there is a problem with the tyre's shoulder, as happened at Silverstone.
Tyre pressure is a key tuning aid, with stability, traction and warm-up characteristics all affected.
At Silverstone, teams ran lower pressures, perhaps below Pirelli's recommended settings.
This makes the tyre move about more as it is supported less by internal air pressure and with the 2013 tyres having stiffer shoulders and more pliable sidewalls, they will deform more and place greater stresses on the shoulder join.
This is the angle of the wheel and tyre assembly relative to the vertical and, at a standstill, the front camber angle is usually around 3.5 degrees from vertical with the rear set at between zero and one degree.
As the top of the tyre tilts inwards towards the centre of the car, this measurement is negative and the inner shoulder will bear more of the load.
As the car moves around the track, the suspension will vary these camber angles by several degrees.
Such an increase in camber increases the stresses on the tyres inside the shoulder.
At Silverstone, the drivers were putting tyres inside the kerb to straightline certain corners, meaning the loads on the inner shoulder of the tyre would be far higher than usual.
Any cuts or imperfections in the tyres could lead to the catastrophic failures seen during the race.
Currently, these set-up tricks remain unregulated (although Pirelli has asked for this to change as soon as possible) so teams are free to run the tyres outside Pirelli's recommendations in pursuit of performance.