Tyred of Pirelli? - Matt Somerfield

(c) Pirelli

Here is another article by JLF1's Technical guest writer Matthew Somerfield, on the talking point of 2012; Pirelli.

Pirelli have come in for a lot of criticism over the last few races from the more avid F1 fans. With Mark Webber taking the win in Monaco we've now had 6 winners in the first 6 races a feat never before seen in F1. With Montreal just around the corner we now have to wonder if we will see 7 in 7. Lest we forget that we still have 3 World Champions amongst the grid that haven't taken a win yet along with plenty of others snapping away for the opportunity.

For most people when referencing tyre wear we look at our own vehicles and see that they are on our cars for thousands of miles.  This is a stark comparison to the world ofF1 tyres which last less than 100 miles.  So taking into account this huge difference in mileage must lead us to believe that the tyres produced for use in F1 are a complex structure.  Made from a weaved nylon and polyester design a Pirelli tyre can withstand temperature and load that it's road going counterpart could never achieve.

Michael Schumacher has been vocal in his distaste for the degradation rate of the Pirelli tyres but we must remember that Micheal’s successful years came in a period where tyres tended to have very little performance drop off (Bridgstones) and re fueling played a much larger part in race strategy. This meant that the driver could literally nail each lap but also leads to a very autonomous / metronomic driving style. The Pirelli tyres however give a see-saw effect and require one of two options:

Tyre Management/Conservation as we are seeing now with drivers eeking out mileage on the tyres perhaps they shouldn't be able to do.

Shorter Runs / More PitStops would allow the driver to drive further on the limit but obviously requires more stops than the first option.

Teams will always want to do the former as it helps to preserve the life of the car/components, takes less risks from crashing under pressure and more importantly means they carry less fuel from the start of the race.

Pirelli have met the criteria supplied by the FIA giving a much more aggressive set of compounds resulting in higher thermal properties and a knock on effect to the Degredation level of the tyres. However I wonder have they gone far enough?Making the tyres degrade even quicker would lead the teams to the second option from above. Many fans love the unpredictability that the tyres have lead to but lets have a quick look at why design also plays a role in how the Pirelli tyres work:

Aerodynamic Influence

The loss of EBD (exhaust blown diffusers) has been a massive hammer blow for most of the leading teams. As we all know energised airflow created by the exhaust gases above the diffuser area used to generate massive amounts of downforce.

This downforce generated at the rear needed to be carefully counter balanced by the equal amount of front downforce. With EBD banned the teams are trying more ways in which to gain back the lost downforce. Some of the teams have adopted neutral exhaust positions where as others are using bodywork and angling of the exhausts to promote flow toward the floor. Due to the inaccurate nature of this flow in open atmosphere an element of tyre warming is inevitable. This may well be accelerating some of the rear tyre degredation we have been seeing.

Suspension

Bearing in mind the loss of additional pressure generated on the rear suspension by the loss of EBD this needs to be balanced up front and so the suspension yo-yo effect begins. Each aerodynamic update presented to the car requires the suspension settings to be tweaked to gain improved traction.

McLarens new higher nose can be seen as the largest representation of this so far this season with a big aero balance shift. Their new nose allows more air to flow toward the leading edge of the floor and then onward to the diffuser. This will require the team to adjust their suspension settings to counteract the additional downforce being generated at the front combined with the loss of some front end downforce.

We all saw last year how far Red Bull were willing to go in terms of pushing the limits of the Pirelli's at Spa when they were adding a pretty serious amount of 'camber' to their setup. (Adding camber leans the tyre in at the top toward the car). This has the benefit of giving a larger 'contact patch' (more surface area of the tyre touching the ground) however the further you lean the tyre the more chance you have of tyre failure and/or changing the character of the tyre as you are effectively using the sidewall of the tyre to do a job it wasn't designed to do. I haven't heard much so far this year about the amount of camber being used but I'd pretty much guarantee the teams are pushing the limits of what is viable.

Weight Distribution

The FIA added the following rule when Pirelli entered the sport for the 2011 / 2012-2013 seasons:

4.2 For 2012 and 2013 only, the weight applied on the front and rear wheels must not be less than 291kg and342kg respectively at all times during the qualifying practice session.
If, when required for checking, a car is not already fitted with dry-weather tyres, it will be weighed on a set of dry-weather tyres selected by the FIA technical delegate.

This effectively narrowed the operating window of many teams who were perhaps running more exotic suspension setups in order to attain better aerodynamic advantage. Rake is an important element in adjusting the area available in the diffuser as the rake increases so does the volume available in the diffuser. EBD allowed considerably more air to flow through the diffuser last year and thus many teams are running with much less rake this year. This is not the only reason though, when running more rake you are effectively pointing the car nose down. This will tilt the weight distribution forward and as we can see from the new rules this is something the FIA is trying to minimise. With those 2 mandated minimum weights combined (633kg's) this only leaves 7kg's of 'freeweight' Due to the minimum car weight of 640kg's. This allows the teams a little more than a bag of sugar to distribute weight how and where they want. Rearward weight should give better traction where as weight placed forward may help those who can generate more airflow to the diffuser gain rear downforce. The weight distribution rule narrows the window available for the teams and so as far as I can tell this rule is much more of a contributing factor to the closeness in racing than the tyres themselves.

I do however see alot of fans angry that Pirelli may have gone too far with their compounds making them degrade too quickly. I think we have to consider that with the aforementioned weight distribution having stronger compounds will only give a linear result.

Driving Style

When a driver finds a setup sweet spot they are able to capitalise on this linearity and drive the tyres beyond their usual operating window much like Sergio and Lewis have done so far this season.
You will probably have noticed that some of the memorable drives from this seasons 5 races have come from drivers out of position who have come back through the field by 'better managing their tyres' I however believe this has more to do

with their lines during those laps.These drivers tend to spend less time caught up with drivers on the same strategy as them and with the aid of DRS overtake cars that have less pace. Ultimately it also means they spend a fair amount of time 'off line' which is essentially a colder surface and remember we are talking about 'Thermal' degradation, yes it may be dustier and have some marbles but it may remove some of the over heating effect from the surface temperature of the tyre. What do you do with your wet or intermediate tyres on a drying track (racing line)? That's right you get off the line and cool them off. Remember Lewis' pass on the 2Toro Rosso cars? Yes it may of been instinctive as a racer for him to take the undercut style but it was not only more aerodynamically efficient (getting out of the turbulent air) but I think perhaps took much less life out of the tyre through a cooler contact patch.  The racing line is a build up of rubber created by reoccurring usage of the same line, as I'm not a tyre engineer I can't be sure but surely this creates a more abrasive surface and in turn heats the tyre more.

In Summary

Let's not be so hasty to jump on the Pirelli hate bandwagon and realise more factors are in play than simply Degradation due to excessive wear.  Pirelli were given a brief by the FIA to provide tyres with a bigger drop off to aid the show and make the racing much closer.  They have achieved this but I feel it's also important to realise that the effect the FIA made on the cars by removing EBD and also mandating weight distribution will also be contributing to the effect.  Many are questioning the tyres due to their degradation rate but we have to remember that all teams have equal footing in terms of rules/car design.  Those that spent more time analysing and designing around the tyre effect are having a more productive season than most.  Lest we also forget that the teams that have been best utilising exhaust effects over the last few years in order to gain downforce have less data and indeed experience in gaining time from suspension setup at lower ratio aero efficiency than teams like Lotus, Williams and Force India.