The Effect of Track Surface on Race Strategy

Considering the intricate array of factors that strategists in F1 and other motorsports must weigh when crafting the optimum race strategy, it might come as a surprise that the track surface itself plays a pivotal role.

The roughness, type, and even colour of a racetrack’s surface significantly influence the level of grip available, which can ultimately be a deciding factor in the delicate balance of winning and losing. This relationship between the track surface and race strategy is a critical element in the high-speed world of motorsports.

Track surface

The surface of most racetracks consists of asphalt, which is a mixture of bitumen binder with an aggregate, such as stones and gravel. Typically, this asphalt is applied on top of layers of crushed rock and stone using the Stone Mastic Asphalt technique.

Interestingly, the stones within the asphalt can have such an effect on the level of grip, that often new circuits from across the world will import stones from specific quarries in the UK to ensure a high-quality track surface.  

Micro and macro roughness

To characterise the texture of different types of track surfaces, engineers analyse the macro and micro roughness. Macro roughness refers to the smoothness of the arrangement of stones, while micro-roughness is the smoothness of the individual stones. 

For example, a surface has a high macro roughness if there are large gaps between the stones and the stones stick out, creating the peaks shown in the green trace in the diagram below. However, if these gaps are filled with material, then the surface has a low macro roughness.

Whereas, if the surface of the stones themselves is rough then the micro roughness is high, but if the stones are polished and smooth, the micro roughness is low.

Tyre grip

There are two ways a tyre generates grip; indentation and adhesion.

Both mechanisms involve the viscoelasticity of rubber deforming asymmetrically which generates a friction force, also known as grip. Indentation is where the rubber is excited by the track’s roughness and adhesion is where a molecular bond forms between the rubber and the track, as shown in the illustration below. 

The roughness of the track significantly affects the amount of friction force generated between the rubber and the track.

If this friction force, or grip, is too low, the tyre will skid over the track’s surface and wear away. This increases the degradation of the tyre which shortens it’s wear life; causing a headache for strategists as they have to redefine stint lengths. 

Track evolution 

The quality of a track’s surface is always evolving year-on-year, day-to-day and even during a session. This is because rubber is laid down in braking zones and at apexes as cars go round the track. This increases the grip level and results in faster lap times. However, rain or wind can remove this layer of rubber over time and the track becomes ‘green’ or ‘dirty’ where grip level is low and lap times are slow. 

Track temperature

The temperature of the track can also play a role in the amount of available grip. Higher track temperatures lead to higher tyre temperatures which can often bring tyres into their working range, increasing grip. However, extremely high track temperatures can induce graining and blistering. On the other hand, low track temperatures make it difficult for the rubber to deform and therefore generate friction. 

This fluctuation in grip is why teams keep a close eye on the weather and track temperature throughout a session. Clear, sunny days will heat up the track quickly, particularly newly laid tracks that are often darker and therefore absorb more heat. Whereas an overcast day can reduce track temperatures by as much as 20 degC (68 degF). 

Resurfacing

Resurfacing of the track is another crucial factor that strategists must consider. Often the top layer of a new surface is sealed with bitumen, resulting in a micro and macro smooth surface. This was the case at the 2020 Formula 1 Turkish Grand Prix where the track was so smooth that the dry tyres could not generate enough grip and when wet, the track became extremely slippery. The following year, the track was cleaned and water blasted, removing this top layer of bitumen and exposing the stones. Grip dramatically improved as the tyres had something to key into, so tyre degradation and lap times were completely different to the year before.  

Another example is the Texas Motor Speedway in 2021. To increase grip for NASCAR’s Goodyear tyres, parts of the track were treated with PJ1 TrackBite, which is a surface usually used on drag strips. Unfortunately, this surface provided minimal grip for Indycar’s Firestone tyres, which restricted the cars to almost a single racing line. Unable to go off-line, this completely changed the lap times and optimum race strategy as pitting was dictated by track position.

Simulating strategy

Unfortunately, there is no direct measure of track condition and so teams have to rely on tools such as RaceWatch to collate all the various data streams into one platform. In this way, strategists can monitor the weather, track temperatures, lap times and more in real-time to understand the state of the track throughout each session as well as across the weekend. Graining front tyres during a practice session on Friday can easily become blistering rear tyres in a race on Sunday. 

To help understand the behaviour of the tyres, strategists define degradation curves for each type of tyre compound. These curves illustrate how warm-up, wear and overheating are expected to change lap times across a stint for each compound.

Track condition, temperature and even just a resurfaced section of track can completely change how they appear, which is why software such as RaceWatch that updates tyre curves in real-time is a vital tool for strategists.

RaceWatch automatically plots a degradation curve for each run of every driver throughout a session. These curves are then averaged to get a more reliable estimate of tyre degradation for each compound, with any unrepresentative runs removed.

Once refined, these degradation curves are used in strategy simulations to predict how the race will unfold for different pit stops strategies and stint lengths. This helps the strategist to define the optimum number of pit stops and which compound to use for which stint to achieve the fastest overall race time.

How to Manage the Effect of Track surface and Optimize Race Strategy

To delve deeper into the complexities of race strategy and the pivotal role of technology in motorsports, a webinar titled “How to Optimize Race Strategy and Analysis” provides invaluable insights.

The webinar features Bernadette Collins, the former Head of Race Strategy for Aston Martin’s F1 Team, as she draws on real F1 race examples to unpack the intricacies of RaceWatch technology:

Webinar viewers will gain a comprehensive understanding of how F1 teams leverage technology to capture more than 1,000 data points per second, powering over 2 million predictive simulations throughout practice sessions, qualifying rounds, and race day itself.

Key Takeaways from the Race Strategy and Analysis Webinar:

• Insight into the technology that underpins analysis in F1 teams.
• The role of predictive simulations in shaping performance outcomes.
• Potential applications of motorsport analysis technology in football, rugby, and beyond.
• An in-depth look at how sports can harness technology for future advancements.

This session is a must-attend for enthusiasts and professionals eager to understand the technological backbone of race strategy in F1 and its potential crossover into other sports arenas.

Article written by: Gemma Hatton