Is Pirelli really to blame?

17/05/2013
FEATURE BY MATT SOMERFIELD

The Spanish GP, held at the Circuit de Catalunya, has for years been a forgone conclusion; rock up on a Saturday, duke it out for the front row of the grid and you're guaranteed to take victory on Sunday. This year that changed and for the first time in years I didn't find myself drifting off in front of the box a third of the way through the race. You will all know I am both a fan of strategy and a defender of Pirelli but perhaps what isn't clear is why the Grand Prix became a four stopper.

I would also like to say that although Social Media has led to my own rapid rise it may also be the reason we are seeing Pirelli take the brunt of the criticism this year. If I may borrow a line from the film Inception:

"An idea is like a virus. Resilient. Highly contagious. And even the smallest seed of an idea can grow. It can grow to define or destroy you."

A symbiotic relationship arose during last season whereby the mainstream broadcast and journalistic media used Social Media to interact with the fans in order to understand their needs and listen to their thoughts. Formula One though, to my eyes, is still behind the curve in terms of Social Media and so a protracted view can rear up. Armed with these views and the wanton need to be both relevant and portray what they feel is the view of the many broadcasters and journalists who have been critical of the tyres. The teams have, of course, also seen the wide-sweeping effects of Social Media and the manipulation of the mainstream media as a way of changing the minds of the fans to suit their agenda. Think about when one team finds an aerodynamic advantage that others haven't, their first thoughts are can we replicate it? If we can't replicate it, can we get it banned? With life being made difficult for the teams by the 2013 Pirellis it seems some are now going for the latter...

So when we look at the facts are these views justifiable? Firstly we must understand that FOM/FIA conducted a survey several years ago in order to get an idea of the general perception of the sport. One of the key areas that was highlighted as an issue to people and the key reason people didn't necessarily watch the sport was the lack of overtaking.

A decision was made to rectify this and in 2009 the sport went through regulation changes to try and solve the problem of overtaking. Part of these changes involved a change from grooved tyres to the slicks we have now. The supplier at the time, Bridgestone, had already furnished us with two compound choices from 2007 onwards but unlike the static compounds we have at present the Japanese manufacturer would alter their hard and soft compounds tailoring them for each track.

When Bridgestone was asked to supply the Slick tyres in 2009 the idea was to return an element of mechanical grip back to the sport which had been taken away by the grooved tyres however, the hard and soft compounds continued to be tailored for each event. Bridgestone always felt that its inclusion in the sport needed to show some road relevance and with the re-introduction of slicks it pulled out of the sport at the end of 2010.

Enter Pirelli, its brief from the FIA was simple produce a tyre that mixes strategy and encourages drivers to overtake. Using Montreal 2010 as the benchmark the FIA had realised that engineering a challenge for the teams could once again produce close racing.

But why are we seeing such a difference this season over previous years? Pirelli was criticized during 2012 as its tyres were often seen to be the differentiator and so it set about changing its 2013 line-up in order to alleviate some of these grievances. The 2012 tyre tended to wear on the shoulder of the tyre and so even though the tyre still had grip it wasn't available to the driver as it was on a section of the tyre unavailable to him. The new construction features a much softer sidewall allowing the platform of the tyre to stay in contact with the track, enlarging the contact patch. In line with this the tread platform was beefed up, as otherwise it would wrinkle under load leading to a non-uniform level of wear. The 2012 construction also led to tyre warming issues (mainly a problem for the front tyre) as the whole surface of the tyre wasn't being aggravated enough and with the stiffer sidewall, energy wasn't being pumped into the tyre.

For 2013 Pirelli also made changes to the compounds lowering the ranges so they are the equivalent of the lower compound of last season. This meant the 2013 hard tyre was equal to the 2012 medium, 2013 medium equals 2012 soft, 2013 soft equals 2012 super-soft and an all new super-soft compound. This was done in order to once again challenge the teams as towards the end of 2012 the teams had resolved their issues with the degradation of the tyre.

So why the dramatic difference when all of the above should lead to more mechanical grip available to the driver?

The area that commentators and journalists alike are not willing or able to talk about: The aerodynamic influence of tyre dynamics. I have talked above about the softening of the sidewall with these tyres so let us now look at how this impacts the aerodynamics of the car.

At the front of the car the tyre's profile is one of the crucial elements in shaping the airflow over the rest of the car. With the tyre deforming much more dynamically over the course of a lap it has therefore become even more crucial for the front wing to manage the direction airflow is deflected around the tyre.

Airflow going inbound of the wheel is managed further downstream by turning vanes, the splitter, bargeboards and sidepod etc, and so changes in these areas may have already been implemented or be included in the current program of design decisions.

Airflow directed around the outside of the front wheel tends to migrate back toward the floor of the car impacting on a key area to which the teams extract performance. The tyre's dynamic changes therefore make the task much more difficult to manage and we find most of the teams are adding 'tyre squirt' slots ahead of the rear wheels as an additional method with which to control the problem and its ongoing effects into the crucial area between the rear wheel and diffuser’s edge that teams aim their exhaust plume.

'Tyre squirt’ is a problem faced by an open wheel car but moreover those using the diffuser as a means of creating more downforce. 'Tyre squirt' is the airflow that is discharged by the rotation of the rear tyres and is sent laterally into the diffuser, this is a problem that the teams faced more with the banning of exhaust blown diffusers (EBD) and off-throttle blowing (OTB) is that of 'Tyre squirt'.

The drawing above shows the implications of 'Tyre squirt' dependant on the aerodynamic influences of the exhaust. (Yellow airflow is air passing around the sidepod, Blue as the diffuser's airflow underneath the car and Red as the exhaust plume). As we can see in the left-hand picture when the exhaust has no influence over the airflow the air received by the tyre is pushed laterally below the floor reducing the diffuser's effect. The middle picture depicts the era from 2010/11 where teams placed the exhaust on the floor of the car directly in the path of the gap between the wheel and diffuser’s edge. This had the effect of cancelling out 'tyre squirt' with the airflow coming around the sidepod instead pushed above the floor into the ‘Coke bottle’ region 'sealing the diffuser'. This is all well and good if you have a consistent flow in the gap but when the driver comes off the throttle the exhaust plume dissipates. In 2011 the teams used off throttle blowing in combination with EBD, and so when the driver came off the throttle the exhaust plume continued to be fed into the gap between the tyre and the floor 'sealing the diffuser' even when the car was going through the corners.

The FIA did its level best to stop this practice when it introduced new rules for 2012, determining the locality and orientation of the exhaust whilst preventing the teams from using as much OTB through engine mapping restrictions.

The teams however now knew the use of EBD was a massive performance differentiator and we ended up with the 'Coanda exhaust, this method is not as full proof as EBD as the orientation of the exhaust channel and throttle position will give a different aerodynamic effect but it still goes some way to gaining a large advantage.

So come on then get to it, why does this affect the tyres? Well, let’s allow these two worlds to collide...

The 2013 tyres by virtue of their sidewall construction move dynamically throughout the course of the braking and turning motions. At the rear of the car their movement is in contrast to the exhaust plume’s influence between the tyre and diffuser's edge, reducing the downforce by virtue of more 'tyre squirt' impinging on the diffuser. Perhaps even more critical though is that dynamic change of ride height will also lead to change in diffuser height thereby also dynamically altering its ability to produce a consistent level of downforce in the corners.

This aerodynamic head scratcher is the principle reason we see the likes of McLaren, Williams and Sauber struggling as they failed to foresee the influence the tyre dynamics could have on downforce extraction.

So how can this aerodynamic problem be causing a degradation issue?

Lateral load / Slip Angle: As the tyre deforms and causes a loss of downforce the tyre slides generating heat and therefore losing grip before once again gripping when enough force is present. When talking about slip angle we must also refer to cornering force, this is the symbiotic relationship between the angle of the tyre and the force exerted on it which produces the grip. More force should equal a higher slip angle but at some point the force exerted can overcome the properties of the tyre as this video demonstrates:

So as we can see the problem is not the fact that teams cannot produce enough downforce, it's that they cannot provide a consistent amount in order to increase the cornering force.

Moving back to Barcelona I have a few things to make points on. Firstly lets think of last year’s compound choices: Hard and soft tyres, what are this year’s equivalent? Hard and medium (With the hard being altered back to a specification akin to 2012's compound before Barcelona) So this rules out the influence of the compounds in this year’s race being a four-stopper.

The race was completed in 1:39:09.145 by Pastor Maldonado in 2012 whilst Fernando Alonso completed the race in 1:39:16.596 a difference of 7.5 seconds. A pit stop at the Circuit de Catalunya is around 18 seconds and so the 4 stop strategy did not make the race last significantly longer. Kimi Raikkonen finished a further 9.3 seconds down the road completing one less stop than the Spaniard proving that 4 stops and flat out driving was the way to go.

If we look back at 2011 Vettel took the same approach as Alonso with Red Bull realising that 4 stops and a more aggressive driving style was the quickest way around. Red Bull was lauded that day for its strategic approach and so now I'm left wondering why we suddenly feel it necessary to condemn the same strategy.

I know many fans were confused by the nature of this race and I do understand where you are coming from but I missed the first 15 laps (live) and several laps throughout as I was working at the same time, but still managed to understand where the strategy was playing out. I'm not drawn by the rumblings of commentators though and instead watch the race for what it is, all the time looking to establish the strategies at play. This perhaps then is one of the failings of the broadcasters, unable to convey the complexities of what's happening on track in a way that makes it easier for the viewer to understand.

Another critique of broadcasters is their use of the team radio and the way in which that information is consumed. For example, Hamilton was told at one stage that Rosberg was coasting more in Turn 3 to save the tyres (slip angle, tyre wear etc) to which he responded he couldn’t go any slower. The commentary was then led down a path that once again condemned the tyres rather than the fact Hamilton had a total disregard for the information his engineer was giving him. (Lest we forget that Hamilton took 4 stops rather than the 3 Rosberg did, losing around 18 seconds of track time and position in the pitlane which had he lifted through 3 might not have been needed.

If you were confused by the 4 stop strategy vs 3 stop strategy know this; those on 4 stops were driving at a quicker pace than those doing 3 stops something you have asked for the drivers to do ('We don't want drivers driving at 80% of their ability') So what do you want? More stops and quicker lap times or conservative driving and slower, tyre protecting lap times?

The biggest problem you see is perception, Ferrari had already conceived a 4 stop strategy, whilst the rest of the field were trying to see if they could do 4. By the time this had been realised they had to play catch up and switch themselves to a 4 stopper (Red Bull being one of the biggest culprits of this IMHO). As you were not fed this information by your respective broadcaster I understand your quandary but I implore you to dig a little deeper, start out by following a couple of teams throughout the race until you find you are able to see the bigger picture. I've been doing this for years, it's not a new phenomenon, we had a similar strategy fight unfold when there was re-fuelling in F1.

Armed with this information I hope I have planted a seed that will spread like a virus enabling everyone to realise that Pirelli has actually done what was asked of it, producing a tyre that enables more strategy and increased grip over a shorter time frame.

At the time of originally writing this article Pirelli hadn't announced its intention to make changes ahead of Montreal to its 2013 tyres and so I feel it's important to add some additional information:

Pirelli’s motorsport director Paul Hembery said: "Our aim is to provide the teams with a new range which mixes the stability of the 2012 tyres and the performance of the current ones."

This is likely to come as both great or bad news depending on which team is receiving the news, but one thing is sure, any changes to the construction of the tyres will levy an aerodynamic change. It is not yet clear how wide-sweeping these alterations will be and whether changes will be made to both the front and rear tyres. Most teams will be frustrated having adjusted their projected upgrade packages around the management of the tyres for the forthcoming races, leaving me pondering the cost of this move.

Furthermore with resources already stretched this year as the teams prepare themselves for the rule changes ahead in 2014 this won't come as good news.

Pirelli finds itself in a no win situation, berated by certain teams and media if they hadn't made changes but equally under fire from those who had made the best of the product so far this season.

Will it ultimately decide the Championship? I doubt it, but it will create a significant swing for this and next year’s development paths.

Matt Somerfield

Article from Pitpass (http://www.pitpass.com):

Published: 17/05/2013
Copyright © Pitpass 2002 - 2024. All rights reserved.