Hurry up and weight

Vyssion & jjn9128 on

The introduction of the halo head protection system for 2018 brought about the seventh increase in the minimum car weight in the last nine years, with another weight increase being promised for 2019; adding 6kg for driver equivalency ballast.

Despite the increasing weight, cars were turning in the fastest lap times ever recorded at some circuits in 2017, with even faster times being set in 2018. So why is this the case? Do F1 cars need to go on a diet, and if so what would the effect on racing be?

Note: this article has been writtten by Vyssion andJjn9128 and full credit go to them. Andy Urlings only added a couple of illustrations.

(Author’s note: We are aware weight is a force so is measured in Newtons, but ‘weight’ is colloquially used to mean mass, which is sufficient for the purpose of this article!)

The minimum car weight in Formula 1 fluctuated throughout the 1970’s and 80’s between 500kg and 580kg (sometimes there were two minimum weights in a season for the naturally aspirated vs forced induction cars). Teams have always tried to push the limits of the minimum weight rule, and not without controversy. Tyrrell were thrown out of the 1984 championship for running underweight and then depositing lead shot into the fuel tank during late pit stops; whilst BAR were banned for two races in 2005 for their secret auxiliary fuel tank, which could empty during the race but was left full of fuel (11.4kg worth) for scrutineering.

However, before 1995 the weight of the driver was not included in the minimum weight of the vehicle, the minimum weight increasing from 505kg in 1994 to 595kg in 1995 to include the driver. Even then the drivers were only weighed once per season, and there are stories of drivers struggling to the annual weigh-in with lead lined helmets to save a few kilograms on their cars. A practice now prevented by the numerous measurements taken after every session of a Grand Prix weekend, and by random in-session scrutineering throughout the qualifying practice sessions.

Minimum car weight only increased slightly between 1995 and 2009, from 595kg to 605kg, but since 2009, the weight of an F1 car has increased by a massive 129kg to a total of 734kg (740kg from 2019); and that’s before 105kg of fuel is added for the start of the race! Despite their recent bloating, Formula 1 cars remain lighter than their top tier rivals; ~820kg in Indycar (including ~84kg of driver and equivalency ballast), 850kg (without driver) in the Le Mans P1 class, and 880kg in Formula E (rising to 900kg with the new season 5 car).

What is the effect of weight on lap time?

To understand how F1 cars weighing 734kg are faster than F1 cars weighing 605kg (contrary to logic) you have to understand how the different performance variables effect lap time. The key performance factors for lap time are weight, power, tyre grip and aerodynamics (downforce and drag), the graph below show how a ten percent change on each of these variables can affect lap time around an average length lap.

Looking at the values the greatest variable is tyre grip, with a 10% increase worth 3.1s per lap. However, as this data comes from publications by teams, it has to be taken with a pinch of salt. In reality the predicted performance increase from the hardest of Pirelli’s 2018 rubber to the softest, of the selection taken to Barcelona for winter testing, is estimated to be 2.6s (Medium>Soft = 0.8s, Soft>Supersoft = 0.4s, Supersoft>Ultrasoft = 0.6s, Ultrasoft>Hypersoft = 0.7/0.8s); which would be a difference in peak grip of between 3% and 4% across each three tyre grouping in the range. As all the teams get the same tyres from Pirelli, the gains from peak grip are marginal and limited to how well each team’s suspension set up gets the tyre into the optimal temperature window. Similarly, the rumoured 60bhp deficit the Honda had to the estimated 1000bhp produced by the Mercedes in 2017 is only a difference of ~6%, so would increase lap time by ~0.8s/lap; not insubstantial in the world of F1, but a smaller difference than the graph suggests.

How this works out in real terms is that for each kilogram of extra weight added, lap time will increase by roughly three hundredths of a second, around an average length lap. Likewise, each point of downforce* found in the wind tunnel is worth three hundredths, each point of drag saved worth six hundredths. Finally, every horsepower found on the dyno and each thousandth of the tyre friction coefficient (assuming 1.6 < μ < 1.8) are worth two hundredths of a second per lap. Within each set of regulations, the minimum weight is fixed, so reducing weight further is not possible, however, reducing the height of the centre of gravity is beneficial; every millimetre lowered reduces lap time by one hundredth of a second per lap.

*a “point” is a unit used by teams during aerodynamic development, aerodynamicists work in non-dimensional coefficients (Cz for downforce, Cx for drag) to remove the effects of air temperature and altitude from development. A “point” represents 1/100 of the non-dimensional aerodynamic coefficient, i.e. if Cz = -3.5 then the car has 350 points of downforce. At 240km/hr (150mi/hr), at sea level with air temperature of 15°C, 350 points is equal to 14.3kN of downforce, or double the weight of the car without fuel.

So where has this extra weight come from?

Cars today are over 1m longer now than a decade ago, to extract extra downforce from the underbody and create ever tighter “coke bottle” waists; the cars are also safer, with the halo, better front, rear and side impact protection, multiple wheel tethers, and 5mm thick anti-intrusion Zylon panels running along the sides of the monocoque.

Unfortunately, though, most of the weight gain has come from the hybridization of the engines. When KERS was introduced in 2009 only a handful of the teams ran with the system, most choosing not to race with it because of unreliability coupled with the penalty of the additional weight, especially if it failed mid-race. To combat this, 35kg was added to the overall weight between 2009 and 2011 (KERS was legal in 2010 even though all teams agreed not to use it) to make KERS viable for teams. Multiplying the effect of weight to the increase shows this increase added ~1 second to the average lap time. Between 2013 and 2015 another 62kg was added to the minimum weight, firstly to accommodate the turbo-hybrid power units (batteries, turbo and intercooler, MGU-H, MGU-K...etc), and then following concerns about some of the drivers being dangerously underweight to meet the 690kg limit; adding another 2 seconds per lap. Finally, since 2016 another 32kg has been added, firstly for the wider cars and wider tyres introduced in the 2017 regulations, to make the cars more visually exciting, and then the halo head protection system, adding a further second to the average lap. Added up over the past decade shows that cars in 2018 should be around 4 seconds slower per lap than when the weight started increasing in 2010.

In reality the cars are not four seconds slower now than 10 years ago. In fact, in qualifying for the 2018 Spanish Grand Prix was Lewis Hamilton was 4.4 seconds faster than the fastest qualifying time from 2007*. The actual fastest qualifying time has fluctuated with changing rules and tyres over the last decade, from between a second above or below the 2007 time up to 2013, before a four second deficit in 2014 and a massive annual improvement of 2.5 to 3 seconds per lap each year between 2015 and 2018 (cars are 9 seconds quicker than at the start of the turbo hybrid era). Incredibly the cars are a whopping 8.4 seconds quicker per lap faster than would be anticipated considering the effect of the increasing weight alone.

* Barcelona is used for this analysis as it is the go-to circuit for testing, while 2007 was the first year the circuit was used with the sector 3 chicane (turns 14/15). The qualifying time is used as it is set when the car is known to be closest to the minimum weight, while the fastest qualifying time is used as up to 2009 Q3 and therefore the pole time was set using race fuel. It should be noted the track was re-laid in the winter of 2018 to remove bumps and improving braking stability potentially improving lap time.

It is incredibly difficult to compare lap times for many circuits going back as far as a decade as only seven circuits on the 2018 calendar were present in their current configuration in 2007. For example, Silverstone has been on the F1 calendar, on and off, for 70 years, but only in its current configuration since 2011, even then only since 2012 using the Abbey pit complex and start line. Hockenheim shared hosting duties with the Nürburgring since Germany returned to the F1 calendar in 2008. Singapore has had the corners around the Singapore sling double chicane, now a left-hand bend, reprofiled twice since its inaugural race in 2008. Even Monaco was shortened by 3m in 2015 when the swimming pool chicane barriers were moved. In the cases where a comparison can be made the same trend as seen with the Spanish Grand Prix occurs: lap times in both qualifying and the race get slower up to 2014, then get faster at a rapid rate up to 2017, and with the exception of Azerbaijan the trend has continued through 2018.

What is it about modern Grand Prix cars that makes them so fast?

Excluding the wet weather sessions from the qualifying data shows how the average lap speed has increased rapidly since the start of the hybrid era, which is not surprising given that lap time is improving. Averaging the speed for the circuits present on the calendar, with the same layout (which is only 11 of the 21 races on the calendar in 2018), since 2011 shows the mean speed reducing up until 2014, before increasing by 15.6km/hr (9.75mi/hr) up to 2017. The key areas where this average lap speed can be influenced are top speed, braking, cornering speed, and acceleration. Top speed and acceleration broadly being influenced by engine power, torque, and aerodynamic drag; while acceleration, braking and cornering speed are influenced by downforce and tyre grip.

Looking at aerodynamic performance over the years is hard to do, as teams don’t like this information in the public domain, even for old cars; but the dominant trend is for increasing downforce with reducing drag, increasing aerodynamic efficiency (the lift-to-drag ratio). The change in downforce production with each year and change of regulations is also greater than drag, which is relatively linear by comparison. 2017 saw a massive increase in downforce over 2016, with a small increase in drag owing to the wider bodies and larger tyres.

Comparing the actual measurements for the cars goes some way to explaining how cars are faster now than when they weighed 605kg. While 4 seconds per lap may have been added by weight, the power-to-weight ratio of current cars is better than the 2.4 litre V8 engine era (2006-2013), around 1360bhp/tonne compared to 1240bhp/tonne for the V8s. As a result, lap time is improved by 0.7s. The current power units also have more torque over a wider band of the rev range than the V8 engines but lose out on peak power when the electrical energy is drained (de-rating). Aerodynamically, the increase in downforce is worth 1.7s per lap, while the small increase in drag is only to the detriment of 0.3s per lap. In total these four parameters are worth 2.1s per lap over a 2008 car.

The final variable in the equation is tyres; from 1998 to 2008, tyres in F1 were circumferentially grooved, but since 2009 tyres have been slick, initially with Bridgestone providing tyres. In 2011 Pirelli took over the official tyre supply with the specific brief of creating a tyre with high degradation properties. This degradation was achieved with a specific set of thermal properties, which meant a narrow temperature window where peak grip could be extracted. In the past few years, tired of shouldering the blame for the lack of on-track action in F1, Pirelli have been designing out the thermal degradation while also producing ever softer compound tyres, the supersoft from 2017 has become the soft in 2018, arguably to the detriment of the strategic element of F1 races.

So how does this all affect the racing, and do F1 cars need to go on a diet?

This is a difficult question to answer; while weight is undoubtedly undesirable in a race car, the negative effect of weight on overall lap-time is more than compensated for by the increase of power and torque. Peak power output as well as fuel efficiency have increased year-on-year since the introduction of the fuel limited, turbo hybrid engine formula in 2014, and gains should continue to be found until the next change of engine regulation in 2021.

Improved engine power mainly counteracts the increased weight in a straight line though; while the added weight, and its associated weight transfer, will make the cars lazy (slower) in the corners. To combat the effect of weight on cornering speeds, aerodynamic downforce was increased significantly in 2017; along with wider and stickier tyres, the cars can now exceed 5g of lateral load in cornering, and more than 6g on the brakes. However, increasing downforce has inarguably been detrimental to wheel-to-wheel racing; while the more durable tyres have also removed the strategic element of Formula 1, with one-stop races becoming the norm throughout the 2017 season. This trend has continued in 2018, although safety cars have helped to add a strategic element, especially at the Chinese Grand Prix.

The combination of more power, higher downforce and stickier tyres will mean the 2018 cars are some of, if not, the fastest ever; to the extent that if lap times continue to drop at the same rate through the season, come the end of 2018, the FIA may once again have to consider slowing the cars for safety (the 2019 rule changes are rumoured to slow the cars by 1.5 seconds per lap).

This opens the question of whether the pursuit of outright lap time is the right thing for Formula 1; should it matter if the cars are a second or two slower per lap if the end product is more exciting on-track action and/or a more competitive/less predictable field? This is the direction Indycar have taken, remember the dry weight is ~90kg more than F1, and the drivers have been raving about the new lower downforce body kits which replaced the high downforce Honda and Chevrolet body kits in 2018. The season opener at St. Petersburg was dominated by series rookie Robert Wickens (until he was skittled off the track in a collision with Alexander Rossi), with fellow rookie Jordan King also leading early in the race. The highest finishing Penske was reigning champion Josef Newgarden in 7th. When was the last time Lewis Hamilton finished 7th in his Mercedes in normal race conditions, or a Haas led the race outside the pitstop window?

There is also the question of where weight could be saved in an F1 car; teams do not carry extra weight by choice, and teams add less ballast now compared past eras of Formula 1 (Ferrari/Mercedes will run more than Sauber/Williams and thus will have a lower COG). As much of weight has been added by the hybrid batteries and added safety features, it would be near impossible to get a modern hybrid Grand Prix car down to the 600kg of the late 90’s. If weight could be reduced though, the power output and aerodynamic downforce would also likely need to be reduced to prevent the cornering speeds of the cars from becoming unsafe. This would likely disappoint any fans who think F1 engines should be producing the 1300bhp of the BMW M12/13 (one lap and throw away) qualifying engines, or the fans enjoying the aerodynamic freedom offered to teams since the 2017 rule change.

There is no correct solution, and each conceivable solution will likely appal some whilst most compromises will unfortunately leave many dissatisfied. It is a problem which strikes at the heart of what F1 is and what it should be going forward. To be at the cutting-edge of technology F1 needs engine regulations which hold the interest the automotive OEM’s; however, the current power units are the cause of the increasing weight, and in the quest for ultimate lap-time the racing has suffered. Rumours about the 2021 engine rules include the removal of the MGU-H, a key component in reaching the 50% thermal efficiency boasted for the current power units (normal road going petrol engines are around 30-35% efficient). This measure may reduce costs for newcomers, but won’t save much weight, will make the engines less efficient, and will also remove the most cutting-edge component of the engines; leaving heavy, low revving power units which are neither interesting to the fans nor the OEM’s. A return to high revving, fuel guzzling, V8 or V10 power units is out of the question, from the perspective of the investment already made for the current power units, remaining at the cutting-edge of technology, and sociologically; with major cities planning to ban the internal combustion engine from their streets from the middle of the next decade, pressure is already increasing on OEM’s to justify continued investment for the internal combustion engine.

Ultimately despite weight increasing almost every year F1 remains the lightest top tier race series and produces the fastest lap-times, even with the 2016 aerodynamic regulations. In the end F1 has to decide if it want to be the pinnacle of motor racing technology, with the fastest, lightest, most powerful, most aerodynamically complex cars; or whether it’s happy to be a second or two per lap slower as the pinnacle of racing competition, with fans tuning in not knowing what the end result will be after the first corner, the overall car weight has very little to do with this as Indycar and Formula E are proving.

Text and analysis by Jjn9128 and Vyssion, additional images courtesy of Andy Urlings.

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