Will Gray

Tech Talk: Pushing tyres to the limits

Will Gray

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After blistering problems in the Belgian
Grand Prix, Pirelli has issued a more cautious tyre usage recommendation for
this weekend's race in Italy - but what's it all mean and why did it happen?

Red Bull suffered serious blistering on
their front tyres in qualifying for the last race at Spa-Francorchamps because
of an over-aggressive set-up that highlighted potential dangers in the way tyres
are used and created questions over how tyre rules are administered.

On a typically inclement weekend in the
Ardennes, limited running in the practice sessions meant that teams could not
carry out their usual pre-race set-up evaluations, which generally see them push
the limits in aerodynamics and mechanical set-up then step back to a reasonable
compromise between performance and tyre degradation.

One crucial part of mechanical car set-up
is camber, which is the angle at which the tyre sits relative to the horizontal
when viewed from the front.

Running a tyre exactly perpendicular to the
road surface would cause the contact patch (the part of the tyre that meets the
road) to slip too much in cornering, so generally a slight inward camber is
used on front tyres to help with the grip when the wheel is turned.

Doing this helps to give a positive steer,
offering more grip on the road and less tyre slip, and in F1 terms it also
helps to get the tyres working harder quicker, bringing them up to temperature
more quickly.

In the kind of wet and drying track
conditions, increased camber can help significantly when the track grip is
marginal - but there is a down side.

When the car is not cornering and is
running in a straight line - and there are a lot of straights at Spa and Monza
- a large inward camber effectively puts more load on the inner part of the
tyre, and that means it is effectively running on a much smaller contact patch.

With more energy going through the smaller
contact patch, it is much easier for it to overheat and eventually blister the
front tyres, as was seen on Red Bull and a number of other cars in Belgium.

Any front-on image of the Red Bull car
shows that is has been running with an aggressive camber in most races this
season, but Pirelli generally recommends a maximum camber of 4 degrees and for
this weekend's race in Italy their recommendation is understood to be for a
reduced maximum camber of 3.75 degrees.

It doesn't sound much of a change, but
given Red Bull is understood to have been running at a camber of just 0.3
degrees beyond the Pirelli recommendation in Spa and ran into such trouble; it
shows that a little amount can make a big difference.

In Red Bull's defence, there was not enough
running in the dry in Belgium to highlight potential issues with excessive
camber, but their efforts to subsequently secure a 'free' set-up change on
safety grounds fell on deaf ears - they could have changed it, but would have
had to start from the pit lane.

Tyre safety has caused its controversial
moments in the past, most memorably in the 2005 US Grand Prix when all Michelin
runners pulled out on safety grounds after a sidewall failure on Ralf
Schumacher's Williams caused by unexpected forces due to the banking at that
track.

But credit must go to Pirelli for
maintaining a sensible head and assessing the dangers very carefully at the
last race and, indeed, for the coming one.

As a tyre manufacturer, they do not want
any team pushing boundaries if it could actually be dangerous - but at Spa,
Pirelli was comfortable that while Red Bull would have to change the tyres
quickly when the race began, they would have to do so because they would be
losing too much lap time to their competitors due to tyre wear long before the
tyre actually became critical from a safety perspective. For Italy, they will
have taken a similarly considered decision.

Right now, these limits remain still only a
recommendation - but Pirelli have not ruled out trying to make it a mandatory
maximum in the future, if they feel the need to take the risk out of the teams'
hands and put it within their own accepted limits to avoid any PR disasters.

Pirelli has acknowledged their reduced
maximium camber recommendation for Italy is on the limit, given Monza's long
straights and high-speed corners, and there will be an even tighter balance for
teams to manage this weekend. Any lower and the car will start to struggle in
high-speed corners, but any higher and it risks the tyres overheating and
blistering.

It will be interesting to see how long the
selected tyre compounds last and how the teams approach the camber issue this
time around - but at least in Italy there should be a reasonable guarantee of
good weather to provide plenty of practice time to evaluate that compromise.

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