The vast majority of body panels on a Formula One car are made from different types of carbon composite materials. Optimising these materials to provide the best compromise between weight and stiffness (or, if some degree of aero elasticity is desired, a lack of stiffness) is an integral part of the Formula One design process. In some areas, for example the bodywork that forms the engine cover, advances in composite materials such as the adoption of spread tow fabrics has allowed fewer material plies to be used and thus weight reduced. However, finding savings in other areas, such as the front and rear crash structures, is more complicated.

Front and rear crash structures at the of the car must fulfil a number of tasks, specifically taking the most aerodynamically efficient form possible, while also meeting the stringent crash test requirements laid down by the FIA. In the past, the most common method for creating these structures was to use an aluminium honeycomb structure, housed in a composite shell. Here, the aluminium would provide the bulk of the structure needed to absorb the energy of an impact.

In recent years though, advances in composite simulation technology and lay-up methods has allowed structures to be created that do away with the aluminium honeycomb, relying solely on the composite for energy absorption. Honda for example, while it was still involved in Formula One, was able to make a 15% weight saving by replacing its aluminium-based nose cone with a solely composite item. The nose cone used four composite ‘pillars’ inside the nose, which provided energy absorbance as well as good structural stiffness.  

Engineers face similar challenges when constructing the monocoque. On the one hand, weight needs to be kept to a minimum, but this cannot be at the expense of chassis performance. Again, information released by Honda sheds an interesting light on this balancing act. The team found that local stiffness around the suspension mounting points had a far greater bearing on chassis performance than overall chassis stiffness. With this in mind, reinforcing plies in areas of the chassis that did not carry suspension mounts were removed, with a consequent 20% reduction in overall torsional stiffness. Meanwhile, the areas around the front suspension mounts and the engine-to-chassis interface were reinforced. Track testing showed that this had no adverse impact on vehicle performance, and netted a very useful 6.5% reduction in weight and a lowering of the centre of gravity by 2 mm.

No doubt the current teams use many other ingenious methods to find similar weight savings and performance gains, but this example shows clearly why it is sometimes necessary to reassess theories about chassis construction that are seemingly set in stone, in order to find that elusive extra performance.

Written by Lawrence Butcher

In addition, the 2014 Formula One rubber is notoriously fickle, with many teams saying it is hard to get it into the correct operating temperature widow without unduly impacting its durability. At the 2014 British GP for example, Andy Green, technical director at Force India, explained that while it was possible to get the tyre to the correct temperature through aggressive warming, this led to very rapid degradation, and finding a chassis set-up that could get the tyre up to temperature reasonably quickly without this being an issue was challenging.  

One widely used tyre model in motorsport is Pacejka’s ‘Magic Formula’, which uses data on slip angle, slip ratio, camber and tyre load to calculate tyre force. However, it misses out on one key variable, which in the closely fought world of Formula One has a huge bearing on performance – tyre temperature. Only when the tyre compound is at the correct temperature will it perform optimally. As a result, if the car does not work the tyre hard enough to get it to this temperature, performance will be compromised. Also, changes in tyre temperature due to slow laps behind safety cars need to be accounted for in race strategies, as does the variation in tyre behaviour from one heat cycle to the next. 

Although the spec tyre supplier, Pirelli, provides teams with a tyre model, most chose to develop their own, which allows for far greater flexibility of development. A few years ago, Honda, which withdrew from Formula One in 2009, developed just such an in-house model, by identifying the elements with the greatest effect on the accuracy of calculations for tyre forces. 

Tyre forces are determined chiefly by the structural deformation of the tyre and the friction characteristics between it and the road surface. The friction coefficient of a tyre changes significantly according to environmental conditions and driving conditions, including road surface roughness, dust on the road surface, tyre surface temperature, tyre slip speed, rubber wear and thermal degradation. 

When devising the model, Honda separated characteristics such as structural deformation and heat transfer – which could be modelled on the basis of theoretical concepts and the results of bench tests – from elements such as the friction coefficient, which depend on track conditions, the parameters for which were established using data gathered on track. By accounting for these variables, Honda was thus able to develop a model that gave a far more accurate picture of tyre performance than would be possible with more readily available models. A brief look at some of the aspects of the model gives a good insight into just how complex a task this was. 

For example, the model treated deformation of the tyre contact patch by dividing it into a belt section and a tread rubber section. Belt deformation was approximated by expressing it as a quadratic function in relation to the position of the tyre contact patch in the longitudinal direction. The deformation obtained in this manner was corrected using the tyre side force, self-aligning torque, internal pressure and longitudinal force, all of which needed to be calculated theoretically or derived from on-track data from sensors recording tyre temperate, wheel loads and so on. 

The complete details of such a model are far too complex to go into fully in a single article, but suffice to say, such models are essential in Formula One these days. However, it also has to be remembered that a model is only as accurate as the data fed into it, so for it to be effective a team must also be on top of all the other aspects of vehicle simulation and data recording. 

The benefits of getting it right are considerable, and not only in terms of performance and development efficiency. Simply through observing tyre behaviour phenomena and analysing the mechanisms by which they take place, previously unforeseen avenues of development and performance enhancement can be discovered.

Written by Lawrence Butcher

To date, it is thought that Ferrari, Red Bull and Mercedes are all using such a coating. It is also thought that the coating in question is a generally available solvent-based product that contains polymers of silicon. The coating is described as a ‘liquid glass’, which is normally clear, but adding a black pigment aids heat exchange between the wheel and the tyre. While a similar effect could be achieved using paint, the added weight would negate some of the performance benefits, adding 50-100 g per wheel. On the other hand, the coating is said to add only about 5 g to the mass of an individual wheel, presenting a negligible weight penalty. This is because, when applied, it is only a few microns thick (and also has a very high surface hardness of around 9 H).

The coating also has secondary benefits relating to airflow within the rim, as its very smooth and glossy finish reputedly helps reduce turbulence. It is not just smooth coatings that are applied to wheels though, and there are a number of heat-resistant coatings available that can be applied with an extremely smooth finish for the same reasons. Another benefit of the high-gloss finish is that it makes the inside of the wheel rim less susceptible to the build-up of debris picked up as a result of brake wear and from the track surface.

Coatings are not the only trick that some teams have used in an effort to improve the thermal and aerodynamic performance of their wheels. In the past, great effort was put into creating carefully sculpted wheels that steered the air where it was most needed. Those days are long gone now though, and wheel design is tightly regulated. However, this has not stopped some teams working within the regulatory constraints to try to garner every last ounce of performance. For example, observers spotted at the end of the 2013 season that the Mercedes team’s wheels featured a ‘textured’ finish on the inner surfaces, while those of Red Bull sported a dimpled effect.

The purpose of such finishes could be twofold. First, the texture could help to reduce the boundary layer of air on the inside of the wheel rim as it rotates close to the brake cooling drum, thus helping to reduce drag in much the same way as dimples on a golf ball. Second, the finish presents a greater surface areas, which combined with a heat-absorbing coating would further increase heat transfer from the brakes into the tyre carcass.

It is steps such as these that highlight the extent of the detail engineering that goes into a modern Formula One machine, and the fact that for the top teams, no stone goes unturned in the quest for performance.

Written by Lawrence Butcher

The main impetus behind this switch was to optimise the front aerodynamic package. A pullrod front suspension system allows for a higher nose position, which helps the flow from the front wing to the underfloor. The pullrod design must be properly executed though, otherwise the suspension geometry can be compromised to a point where the performance gain given by the improved aerodynamics is largely cancelled out by a reduction in mechanical grip due to loss of suspension compliance.

Looking at McLaren’s MP4-28, the location of the horizontal suspension members were positioned in such a way as to smooth the airflow from the front wing. This is achieved by moving the suspension members clear of the front-wing vortex (shed from the inboard end of the front wing flaps). This vortex is important for downstream flow around the barge boards and underfloor. Thanks to the location of the spring and damper units at the bottom of the nose assembly (rather than the top, as in a pushrod system), there is also a small benefit to the centre-of-gravity height

Rear suspension systems have also been developed extensively by some teams. One general trend has been a move by most of them to pullrod-actuated rear suspension systems, thanks to the tighter rear bodywork packaging such a set-up allows. The gains teams have found must be considerable in order to account for the widespread adoption of the layout, given the compromise it presents in terms of suspension performance. Notably, that fact that lifting the rear lower wishbones and toe links up to rear axle height – as in a pullrod design – significantly reduces rear suspension stiffness.

The biggest suspension-related talking point of the 2013 season was the public appearance of Mercedes’ interlinked suspension system, dubbed FRIC (Front Rear Interconnect). Interlinked front and rear suspension is not a new concept in Formula One – it was a feature on active suspension cars such as the Williams FW-14B in the 1990s – but since such systems were outlawed it has taken engineers a long time to develop passive systems that are both effective and fall within the regulatory requirements.

In 2011, both Mercedes and Lotus developed passive systems, although the details of their operation have been kept under wraps, and evidence of the Mercedes system’s existence only came to light during 2013. Lotus initially developed an hydraulic set-up linked to the braking system, but this was deemed to contravene the technical regulations and so was outlawed. Mercedes, however, has managed to develop a system that controls the pitch of the car using linked front and rear hydraulic systems; it is thought that the system also controls roll.

The intention behind such systems is to maintain a constant ride height, regardless of whether a car is braking, accelerating or pitching. This in turn ensures that the aerodynamic balance is kept as consistent as possible, ensuring maximum downforce. It is thought that several other teams have developed similar systems, although none have been willing to reveal details. However, Ross Brawn has been quoted as saying that since Formula One cars were invented and aerodynamics understood, the compromise between suspension and aerodynamics has always been a compromise. Essentially, the FRIC allows this compromise to be reduced, allowing for some chassis compliance while also ensuring a predictable aero platform.

Given the creativity of some teams within the bounds of the outgoing technical regulations, it will be fascinating to see the new approaches – and technical loopholes – the 2014 rules will bring to light.

Written by Lawrence Butcher

Beyond the basic parameters that govern the way a car’s steering behaves, the most important contributor to a Formula One car’s steering performance is the power assistance. The regulations ban electronic or electro-hydraulic power steering, so teams have to rely on hydro-mechanical assistance, section 10.4.2 of the 2014 technical regulations stating, “Power-assisted steering systems may not be electronically controlled or electrically powered. No such system may carry out any function other than reduce the physical effort required to steer the car.”

In essence, this means teams cannot create steering systems that adapt the level of assistance given to the driver according to changing conditions. Creating systems that provide the level of consistency and feel the top drivers need to be able to extract maximum performance from a car – regardless of variations in factors such as downforce or fuel load, while remaining ‘passive’ –  is not easy. Note the well-publicised problems that Kimi Raikonnen faced in extracting performance from the Lotus E20 during the 2012 season, when the car’s power steering failed to provide the level of feedback his driving style required. 

Most teams use the same components as the basis for their power steering system, based around a rotary power-steering valve produced by the same company that supplies their hydraulic valves. The regulating valve is very similar to the electro-hydraulic servo valves found throughout the car for actuating systems such as gear selector mechanisms, but instead of the actuation signal being provided by a torque motor, it is created by a torsion bar or linear springs in the load path of the steering.

As the steering load increases, it creates a displacement in the torsion bar that is linked directly to the spool which, as is the case with an electro-hydraulic valve, provides a pressure differential to the ends of the steering rack, creating the power assistance. The valve’s construction features two concentric sleeves connected by the torsion bar. In operation, torque applied in either direction rotates the inner and outer sleeves relative to each other. This in turn opens flow-metering ports that direct high-pressure oil to one side of the assist actuator.

The valve uses a closed-centre circuit to minimise energy consumption and yet still offer high positional accuracy and repeatability. Due to the high fluid flow rates in the valve, the steering system remains stiff – not in terms of resistance to inputs but in relation to accurately translating driver inputs according to wheel movement. To tailor the systems to different drivers’ preferences, or to variations in car set-up, the internal valving can be adjusted to alter the response rate.

As the regulations are unlikely to change in relation to steering system design, it is probable that this method of power assistance is likely to remain in use – albeit with the inevitable refinements – for the foreseeable future.

Written by Lawrence Butcher

This has placed both Pirelli and the teams in an unusual position. Pirelli has had to build a less than optimal tyre, one that will degrade at a set rate on all the different track surfaces, while the teams have had to try to gain an understanding of the tyre’s characteristics and strike a balance between outright pace and tyre preservation.

As was highlighted at the 2013 British GP, this balance is not always reached, with the teams’ efforts to extract every iota of performance from the tyre package ultimately leading to catastrophic failures. In this case, some teams were running the tyre outside its recommended operating parameters to exploit a performance gain, at the cost of reliability (and safety).

The key reason behind these failures appears to be the fact that the Pirelli tyres are ‘sided’, due to the inner reinforcements being laid up in such a way as to perform optimally when fitted on a particular side of the car. Teams had discovered that sometimes it was preferable to run tyres on the ‘wrong’ side, presumably because this changed the tyres’ behaviour in one manner or another. Unfortunately this meant that when subject to a specific set of operating conditions – no doubt contributed to by the teams running more camber and lower pressures than Pirelli recommended – the rear left tyre failed spectacularly.

As a result of these failures the FIA has now regulated against such practice to prevent further problems. This will see teams having to stick within Pirelli’s recommendations for camber and caster settings, and run the tyres on the intended sides. Also, Pirelli is introducing a revised tyre construction, with a Kevlar rather than steel belt in the tyre’s structure. The result of these revisions should prevent further problems but will lead to a renewed race among teams to master the revised specifications.

Teams understandably want to gather as much information about the tyres they are using under both race and test condition from which they can draw conclusions about tyre performance and degradation. The two key areas which can be measured are tyre temperatures and pressures.  

In the past, tyre temperatures could only be measured when a car was in the pit lane, using a pressure gauge and a thermal probe. Miniaturisation of infrared-sensing technology, however, has allowed tyre temperature measuring equipment to be incorporated into a car’s sensor package, providing real-time information on tyre condition.

There are three key methods for measuring tyre temperature – external infrared (IR) sensors mounted close to the tyre, infrared cameras and measuring devices incorporated into the wheel to measure carcass temperature. Initially, ‘single-channel’ IR sensors were used to measure the external temperature of a tyre, but they could only monitor a narrow strip of the tyre surface, so an overall picture of tyre temperature could not be gained. This disadvantage has now been overcome with the development of multi-channel IR sensors that can measure up to eight sections of tyre, all packaged in a unit weighing about 15 g. Versions of these sensors have also been mounted within the wheel rim itself, with a wireless connection sending the signals to a receiver unit. A glance at the rear floor of many cars in the Formula One paddock will reveal an array of miniature IR sensors pointing at the rear wheels.

IR cameras tend to be used only during testing sessions, because they are relatively bulky items and thus difficult to package effectively. Their main advantage is that they provide a complete overview of tyre temperature distribution, and can be used to assess factors such as heat soak from the brake rotors.

Monitoring tyre pressure is of equal importance to temperature readings. Pressure is dynamic and increases as the gas in the tyre heats up and expands, and it is vital to track the tyre’s operating pressures to ensure it is optimal. Wireless tyre-pressure monitoring systems are now the norm in Formula One, and consist of a sensor unit mounted on the tyre valve stem and a receiver unit in the main control electronics system.

As with temperatures, tyre pressures would in the past have been checked in the pit lane, but they varied from on-track pressures as the tyres cooled coming into the pits; now though, pressures can be logged dynamically as a race progresses. Some of the latest systems even combine pressure and temperature measurement in a single unit using a shared ECU, providing an integrated and therefore more compact solution.

Even with such comprehensive monitoring, Silverstone showed that teams can still be caught out by the unpredictable nature of the Pirelli rubber. It was for this reason that several teams protested against changes to the tyres earlier in the 2013 season, as they felt they had a better grasp than the opposition of the rubber’s foibles. Rest assured though that, with the introduction of a revised tyre construction – and tighter controls on how the tyres are used – engineers will be wanting to gather more data than ever on their racecars’ humble rubber boots.

Written by Lawrence Butcher

The wheel cannot be viewed in isolation, and the various designs developed by teams to condition the airflow through the wheel are dependent on other parts, such as the brake cooling ducts, to be effective. The flow coming off a car’s bodywork, notably from the front wing, also plays a key role.

Over the years, various teams have gone to great lengths to optimise this area of a car’s aerodynamics; the biggest developments took place over the 2006 and 2007 seasons. Instead of simply sculpting the wheel, teams – notably Ferrari – began to use disc-shaped devices that covered the outside of the wheel but that did not rotate.

Making these devices work effectively was no easy task, however, as Pascal Vasselon, of the then Toyota F1 team explained in 2007. “The effect of the front wheel blanking is not something you can capture very simply,” he said. “We now have some experience with it, and clearly it can have a totally different effect according to the rest of the flow structure over the rest of the car. It’s a powerful item, and you can use it in different ways. It’s not only a drag reduction item; it really can change a lot of things in terms of front-wheel wake – you are of course playing with the font wheel wake. It requires careful tuning according to the rest of the car.”

Over the next four years these devices developed into some extreme designs, which in some cases even ended up being extended around the rear of the tyre. Despite the sweeping regulation changes introduced in 2009 to ‘clean up’ the aerodynamics of the cars – intended to reduce the impact of a car’s wake on the cars behind – wheel covers managed to survive. Come 2010, however, the FIA decided they had to go, and revised the regulations to eliminate them.

Ferrari managed to circumvent the new regulations by incorporating an aerodynamic device into the wheel structure itself. This was a cunning move, as rims must be homologated for the whole season, and thus none of its rivals was able to copy the design. Suffice to say, the FIA felt these went against the spirit of the regulations, and for 2011 introduced regulations strictly governing the form of the wheels. This hasn’t stopped teams pushing their development though, and many have devised new means to improve the flow conditions around the wheels.

2012 saw Williams develop a ‘scoopless’ brake duct for the FW34, in an effort to help control the airflow in the area between the wheel and the chassis, while still helping to condition the flow around the outside of the wheel. The design achieves this by using a hollow axle that terminates before the wheel nut and is thus within the regulations. The air is channelled from the brake duct through the axle and out over the wheel rim, the duct being fed by a small gap between the top of the duct and the inside of the wheel.

2013 has seen several other teams adopt similar solutions, as well as further developments to channel air out through the front axle. Red Bull tried a similar solution with the RB8 in 2012, but the design vented air outboard of the wheel nut and was thus deemed illegal.

The fact that teams will dedicate so much ingenuity and effort to such relatively small aspects of a car’s design highlights the level of design optimisation the current generation of cars achieves.

Written by Lawrence Butcher

Like every other aspect of a racecar design, these areas are subject to sustained and strenuous efforts to reduce mass and increase performance without compromising structural integrity and safety. This has led to the use of advanced composite materials such as carbon fibre in the manufacture of parts previously produced in metals.

Carbon brakes, originally developed for use on aircraft, were first tested on a Formula One car in the late 1970s, and since the mid-1980s all Formula One cars have been equipped with them. The manufacture of brake friction material begins with same basic fibre as that used in the production of the carbon fibre fabric from which racecar chassis are made – PAN (polyacrylonitrile). It is, however, processed in a wholly different way, being passed through carbon deposition and high-temperature oxidation stages lasting several weeks that transform its molecular structure and result in a material that as well as offering lower weight relative to metal brakes provides greater durability and higher thermal capacity.

This means drivers can rely on shorter braking distances throughout a race, which was not always the case with the previous generation of metal brake discs. These gains were not without cost though, and a long development path was necessary to provide sufficient cooling of the discs, pads and calipers and other parts in their vicinity before the use of carbon brakes became practicable.

Carbon fibre composite materials have been used for the manufacture of suspension components since the early 1990s. The primary advantages they offer over metal suspension parts are lower weight and higher stiffness per unit weight, but they can also fulfil an aerodynamic function. If the front suspension is correctly configured then the track rod, even when steered, can remain in the same plane and in concert with the top wishbone legs, allowing an aerofoil section to be formed by these two links.

This provides a slender frontal area with a large plan area that generates lift that can be used to redirect the upwash from the front wing and clean up the downstream flow to the top of the sidepods, the diffuser and the rear wing. The stiffness of composite suspension elements has also been a contributing factor in the reduction of the range of suspension movement on a Formula One car. Typically the vast majority of this is catered for by deformation of the sidewall of the tyre.

Carbon fibre composite suspension uprights and wheels have been produced and evaluated in the past in Formula One, but there are concerns over certain characteristics of these materials in such applications, including the difficulty in designing a true three-dimensional composite material capable of handling complex and multiple stress directions. Techniques like z-pinning can help but generally large, relatively lightly loaded structures are the best applications for composites.

On items such as a piece of bodywork or a wing, these loadings are more easily defined and the stresses are easier to predict, making it relatively easy to design a laminate that can handle the loads in the most efficient way. Such considerations would seem to make the future widespread use of carbon wheels and uprights in motorsport applications unlikely. Indeed, the current FIA Formula One regulations proscribe the use of carbon fibre wheels and instead require them to be made from magnesium alloy, and suspension uprights to be made from aluminium alloy.

Fig. 1 - A Formula One car’s carbon fibre suspension links perform mechanical and aerodynamic functions

Written by Alan Lis