In vehicle dynamics, slip angle (also known as sideslip angle) is the angle between the actual direction of travel of a rolling wheel and the direction towards which it is pointing. Slip (usually described as percent slip), is the relative motion between a tyre and the road surface on which the tyre is moving on. This slip can be generated either by the tyre’s rotational speed being greater or less than the free-rolling speed, or by the tyre’s plane of rotation being at an angle to its direction of motion. Fig.1 shows a top view of how slip angle occurs when the vehicle is turning right.

It is called slip angle, because the part of the contact patch that is to the outside of your turn is moving faster than the wheel itself is in the direction it (the contact patch) is pointing , while the part on the inside is moving more slowly. Since the outside part is moving faster than the tyre it must be slipping and hence is the name of ‘Tyre Slip’. The inside part is gripping better than it would if moving in a straight line. For this reason, the contact patch ‘walks’ itself into the turn.

Mathamatical model of slip angle

The slip is generally given as a percentage of the difference between the surface speed of the wheel compared to the speed between axis and road surface. Fig.2 shows that slip angle is the vector sum of wheel forward velocity and lateral velocity. Mathematically, slip could be represented, as:

where , w is rotational speed of the wheel, r is wheel radius and v is vehicle speed. This indicates that a positive slip means the wheels are spinning and negative that they are skidding. Locked brakes, wr = 0, means that slip is -100% and spinning on the spot, v = 0 and wr ≠ 0, means that ∞.

Slip angle , therefore, is the angular difference between the direction the tyre contact patch with the road is pointing and the direction of the wheel (Fig.3). In actual case, the tyre tread does not point in the same direction as the wheel. This is because a tyre is being made of rubber, the sidewalls deform, and the tread pattern itself can ‘squirm’ when the wheel is turned from the straight-ahead.

In fact, modest slip angles are ‘good’ as tyres generate progressively more grip with increasing slip angles (Fig.3).For every type of vehicle and tyre the modest slip angle or the good slip angle is different and for all the tyres in your car, the slip angle might be different at any point of vehicle dynamics.When the limit exceeds, where after no further grip is generated. Thereafter, increasing slip angles are ‘bad’, and the tyre will tend to lose grip. Because of the slip angle, the contact patch of the tyre (Fig.3) need not be in the same orientation as the whole wheel, often lagging a few degrees behind. Greater the slip angle will obviously mean that the larger portion of the contact patch is slipping (Fig.3). At some point there is so little part of the contact patch that there is no slipping, which means that traction is lost and the tyre begins to slide. As the tread element moves through the contact patch it will be deflected further from the wheel mid-plane(Fig.3). This deflection gives rise to the slip angle, and to the cornering force.

Tyres seem to operate at their peak performance when they are under a few degrees of slip angle, they generate the most grip at that particular slip angle. For race and high performance tyres this optimum slip angle is around 6 to 10 degrees while this number is a little lower for street tyres (Fig.4).

Measurement of slip angle

There are two main ways to measure slip angle of a tyre: on a vehicle as it moves, or on a dedicated testing device. There are a number of devices which can be used to measure slip angle on a vehicle as it moves; some use optical methods, some use inertial methods, some GPS and some both GPS and inertial.

Various test machines have been developed to measure slip angle in a controlled environment. Sensors measure the force and moment generated on a dynamic vehicle, and a correction is made to account for the curvature of the track. Other devices use the inner or outer surface of rotating drums, sliding planks, conveyor belts, or a trailer that presses the test tyre to an actual road surface. These days computer simulation models are available for measuring tyre slip angle. Technicians can use a simple tyre finite element model to generate lateral, tangential and radial tyre accelerations for a fixed load and slip angle. The profiles are validated by using experimental data. The simulated acceleration profiles are used for the estimation of slip angle and tyre/road friction coefficient.

Effects of slip angle

Each tyre will have its own slip angle. A tyre that is not slipping has a slip angle of zero degrees. The ratios between the slip angles of the front and rear axles will determine the vehicle’s behavior in a given turn. If the ratio of front to rear slip angles is greater than 1:1, the vehicle will tend to understeer, while a ratio of less than 1:1 will produce oversteer (Fig.5).

Actual instantaneous slip angles depend on many factors, including the condition of the road surface, but a vehicle’s suspension (Fig.6) can be designed to promote specific dynamic characteristics. Incidentally, a vehicle suspension system may include; Coil spring, Leaf spring, Hydraulic and Air Spring or their combinations. This is very important for racing car as they need to take sharp turns on high speeds.

A principal means of adjusting developed slip angles is to alter the relative roll couple (the rate at which weight transfers from the inside to the outside wheel in a turn) front to rear by varying the relative amount of front and rear lateral load transfer. This can be achieved by modifying the height of the roll centers, or by adjusting roll stiffness, either through suspension changes or the addition of an anti-roll bar. Because of asymmetries in the side-slip along the length of the contact patch, the resultant force of this side-slip occurs away from the geometric center of the contact patch, a distance described as the pneumatic trail, and so creates a torque on the tyre.

Bridgestone will supply tailored-made tyres for Lamborghini’s Huracán STO, which will be launched in 2021.

Bridgestone ensured the high-performance tyre can maximise the Huracán STO’s traction, handling, control, and extreme overall performance.

Key to the tyre’s success in maximising the super sports car’s performance is the combination of pattern and cavity design. The Potenza tyres apply an asymmetric tread design for enhanced steering response and cornering stability, and an internal crown structure that distributes footprint pressure evenly when cornering.

As well as the road-focused, custom-developed Potenza fitment, Bridgestone will also be providing a track-oriented, road-homologated version of the tyre that applies “race” technologies to maximise the vehicle’s track performance, especially in dry conditions.

Steven De Bock, VP Consumer Replacement and OE at Bridgestone EMIA, said, “It’s been a pleasure for our team to work so closely with Lamborghini for the first time, and on such an exciting project. The Huracán STO is an incredible piece of engineering that deserves a custom tyre that can fulfill its full potential. I can proudly say that Bridgestone has delivered such a high-performance tyre. It has been fantastic for the team to have worked on a project that is at the forefront of technology in so many ways.”

Hankook, one of the major global tyre brands, has started testing and development operations at its new ultra modern facility in Spain.

The testing facility has been set up on the premises of the Applus+ IDIADA Group and can also cater to European premium car manufacturers that have their own demanding tyre tests. The facility is completely automated and will host a 20-member team from the Spanish testing centre, which is affiliated to the Hankook Europe Technical Centre.

Klaus Krause, Head of European Research and Development Centre, said, "With the further expansion of our testing capacities in Spain, we are reaching the next level together with our local partner Applus+ IDIADA."

He also added, "We are confident that the newly installed testing facilities in particular will significantly improve our efforts to provide the best tyre testing conditions and services to our employees and customers. In addition, we will also be able to conduct significantly more tests on site." (TT)

ASCENSO introduced a construction tyre - BLB 730- which is used for boom lift vehicles used in construction and other industries. It comes with several features that cater to the unique needs of aerial lifting equipment.

The BLB 730 tyre is available in different sizes to fit various boom lift vehicles. This range of sizes provides versatility and compatibility with different types of aerial lift work platforms.

“ASCENSO's BLB 730 tyre is a significant advancement in specialised equipment for the construction industry. It focuses on load capacity, stability, traction, and durability to improve the performance and safety of boom lift vehicles. Whether working at heights or manoeuvring on tough terrains, this tyre offers reliability and durability for efficient operations,” said the company in a statement.

The BLB 730 tyre is built to handle heavy loads and stabilise boom lift vehicles. It has solid lugs and a more extended shoulder design, which ensures good traction and prevents slipping during operation. This is important for safely carrying heavy weights at high elevations. ASCENSO has used a special rubber compound in making the BLB 730 tyre, making it durable and long-lasting, resulting in less downtime and more productivity on construction sites.

To make the tyre even better, the company has optimised its inner volume to reduce tyre fill consumption, reducing the risk of tyre punctures, minimising the need for maintenance, and keep the vehicles running smoothly.

Falken Tyre Europe is an official IHF Men's World Championship 2023 partner for the upcoming tournament, the company has announced. The tournament is taking place at nine venues in Sweden and Poland from 11-29 January, 2023. Falken Tyre claims that the partnership was organised by the sports marketing agency SPORTFIVE. SPORTFIVE is responsible for exclusive marketing and media rights for all IHF World Championships until 2031.

Falken Tyre claims that this is its second agreement with the International Handball Federation. In addition to title and logo rights (Official IHF Men's World Championship 2023 Partner), the company has also secured advertising rights, including the Falken logo in each goal and centre circle of the courts, as well as the presence of Falken branding in the official tournament social media communications and print materials. According to Falken Tyre, this is complemented by 30-second video ads that will be shown on the big screens in the nine sports halls before the start of each match and at half-time.

Sharing his views, Robert Müller von Vultejus, Chief Growth Officer at SPORTFIVE, said, “With Falken, the IHF World Handball Championships have secured a great partner who is positioned with far-reaching influence in the relevant core markets. We are delighted to have been able to bring two global partners together for one of the most exciting sporting events of next year.”

Markus Bögner, COO and President of Falken Tyre Europe GmbH, explained, “Handball isn’t just of great importance in Europe, but all over the world, which has led us to partake in this top-level tournament once again. The fact that the international tournament is taking place in countries that are among our core markets is another great reason for our involvement. We can also look back on a long partnership with our colleagues at SPORTFIVE, who always offers us excellent opportunities that are an excellent fit for the Falken brand, which stands for enthusiasm, performance and achievement.”