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.

Indian tyre manufacturer Apollo Tyres Ltd reported a 3% increase in annual revenue to INR 261.23 billion for fiscal year 2024-25, while its net profit fell 35 percent from the previous year.

The company, which markets its products under the Apollo and Vredestein brands, saw its operating profit decline to INR 35.71 billion for the full year, compared with INR 44.47 billion in the previous fiscal year.

For the fourth quarter ended March 31, Apollo Tyres posted a revenue of INR 64.24 billion, up 3% year-on-year, while quarterly net profit dropped to INR 1.85 billion from INR 3.54 billion in the same period last year.

"We acknowledge that our performance over the past few quarters has not met industry benchmarks and our own expectations. After a thorough internal review, we have identified the key challenges that contributed to this underperformance," said Onkar Kanwar, Chairman of Apollo Tyres.

"With targeted strategies now in place to address these issues, we are confident in our ability to deliver stronger results in the coming quarters," he added.

Apollo Tyres, which has manufacturing facilities in India, the Netherlands and Hungary, distributes its products in over 100 countries.

Elmer Wiemer, Chief Financial Officer and designated Chief Executive Officer of Heuver Group, has passed away. The group shared the sad news in a statement announcing that he passed away on 4 May at the age of 48 after a brief illness.

Wiemer has had a lasting impact on the Heuver Group since he took office in 2020. As CFO, he played a pivotal role in bolstering the course, advancing the organisation's professionalism and attaining long-term success. His strategic vision and astute financial sense were always bolstered by a strong sense of accountability and a kind, humane leadership style.

“He was a true inspiration. Elmer’s legacy is tangible in the way we work together, in the culture he helped shape and in the ambitions he helped realise. We lose in him not only a leader, but also a warm personality, a dedicated colleague and a dear friend,” said Heuver Group management.

Goodyear has launched the award-winning Goodyear Eagle F1 Asymmetric 6 tyre in the United States and Canada. The premium summer tyre has emerged the winner in the 2025 AutoBild test for ultra-high-performance (UHP) tyres and is aimed at a wide range of sporty and luxury cars, crossovers and SUVS.

With its unique tread composition that optimises rubber-to-road contact, the Goodyear Eagle F1 Asymmetric 6 offers responsiveness and stability for dynamic driving. While the flexible tyre compound provides better grip in hot weather, the asymmetric tread pattern guarantees rapid responsiveness and traction in turns. To guarantee a peaceful, pleasant ride, the tyre pattern and lightweight design also reduce road noise. Goodyear's SoundComfort and SealTech innovations are two notable features found in certain Eagle F1 Asymmetric 6 fitments. For a more peaceful and elegant driving experience, SoundComfort reduces road noise, while SealTech successfully seals punctures up to five mm. Because of its high load rating and low rolling resistance, it is perfect for contemporary SUVs and electric cars, which require more from their tyres in order to maximise economy and range.

Nearly 90 percent of SKUs for the Goodyear Eagle F1 Asymmetric 6 are 18 inches or greater, with over 100 sizes available in the 17–23-inch range. Numerous well-known automobiles, such as the BMW M3/M4/X3/X4/X5/X6/X7, Audi A4/S4/A5/S5/A3/S3, Mercedes C-Class, Porsche Macan/Boxster/Cayman and Cayenne, and Tesla Model S, may be fitted with the Goodyear Eagle F1 Asymmetric 6. Customers may feel more secure about their purchase with the Goodyear Eagle F1 Asymmetric 6's 30,000-mile (50,000-kilometre) tread life limited guarantee. It is available at authorised Goodyear retailers across the United States and Canada.

Ryan Waldron, President, Goodyear Americas, said, "The Goodyear Eagle F1 Asymmetric 6 represents the next evolution of ultra-high-performance summer tyre, delivering precision, grip and comfort for drivers. As an award-winning tyre designed for a wide range of sporty and luxury vehicles, including the larger rim sizes on many of these vehicles, it provides a driving experience tailored to today's most premium enthusiasts. We're proud to introduce this globally recognised product to North America, bringing advanced technology and innovation that keeps drivers confident on the road."

Toyo Tires reported record first-quarter sales of 135.5 billion yen ($880 million), marking a 6.2 percent increase year over year and reaching its highest level since adopting its current accounting period in 2013. Despite the top-line growth, operating income fell 13.7 percent to 22.4 billion yen due to rising raw material costs and foreign exchange headwinds.

“Strong sales of large-diameter tyres in North America drove revenue growth but couldn’t fully offset higher production costs,” said the company in its earnings statement. The Japanese tyre maker saw a 7.7 percent sales increase in North America, which remains its largest market.

Profit Squeeze

Ordinary income plunged 42.7 percent to 18.3 billion yen, while profit attributable to owners dropped 41.4 percent to 13.5 billion yen, primarily due to foreign exchange losses from the yen’s appreciation. The Japanese currency strengthened to 154 yen per dollar during the quarter, compared to 146 yen in the year-ago period.

The company maintained its full-year forecast, projecting annual sales of 585 billion yen, up 3.5 percent from FY2024. Operating income is expected to reach 85 billion yen, down 9.6 percent , with operating margin declining to 14.5 percent from 16.6 percent last year. The annual dividend forecast is 125 yen per share, up from 120 yen in the previous fiscal year.

“Assuming tariff impact can be absorbed with appropriate measures, earnings forecasts for FY2025 remain unchanged,” the company stated, maintaining its dividend payout ratio target of 30 percent  or higher.

Production and Expansion

The tyre maker plans to increase production volume by 6 percent in FY2025 compared to the previous year, with significant growth in both Japanese and European operations. First-quarter global production volume was 59,100 tons, representing 98 percent of the previous year's level.

Capital investment for FY2025 is projected at 35.6 billion yen, up from 25.6 billion yen in FY2024, signalling continued expansion despite market headwinds. The company has invested 194 billion yen in capital expenditures over the past five years.

Market Conditions and Raw Materials

Raw material costs continue to pressure margins, with the company projecting a negative impact of 10.5 billion yen for FY2025. Natural rubber price increases are expected to cost 7.4 billion yen, while petroleum products will add 2.0 billion yen in costs, and other materials will contribute 1.1 billion yen to the cost pressure.

First-quarter sales volume showed strong recovery in the Japanese replacement tyre market, reaching 97 percent of the previous year’s level. In comparison, North America demonstrated robust growth at 105 percent year-over-year.

Product Innovation and Corporate Initiatives

The company recently launched premium tyres for high-roof kei cars in Japan with enhanced wet grip performance. These tyres feature eco-friendly materials that improve wet braking performance by 12 percent while reducing rolling resistance by 9 percent.

In March, the company introduced new SUV tyres designed specifically for quiet city driving that meet the “Low Car Exterior Sound Tyres" voluntary standard established by the Japan Automobile Tyre Manufacturers Association.