Toe angle
The toe angle is an angle that plays a key role in the overall axle geometry and affects the vehicle’s behavior on the road. The toe angle has a significant impact not only on the driving characteristics of the vehicle but also on tire wear.
Simply put, the toe angle is the angle formed by the wheels of one axle when viewed from above, see the image below. This angle is important for the correct wheel-to-road alignment geometry. The toe angle affects the driving characteristics of the vehicle, tire wear, and fuel consumption.
Definition of Toe Angle:
The toe angle δ is the projection of the angle between the center planes of the wheels of one axle onto the road plane. If the front of the wheel is angled towards the longitudinal axis of the vehicle, we talk about toe-in (positive toe). If the front of the wheel is angled away from the longitudinal axis, it is called toe-out (negative toe).
Typically, toe is determined for both wheels together as the so-called total toe. Toe values are usually given in degrees or in millimeters. Millimeter values are based on the difference in distances between the edges of the rims at the front and rear of the wheels, see the image above. Common angular values of total toe for passenger vehicles range from 0°-30′. The toe is distributed evenly between the right and left wheels, with each wheel being turned by half the total toe.
Whenever possible, toe is checked and adjusted on all wheels of all vehicle axles. It is typical and well-known to adjust the front axle toe by adjusting the length of the steering tie rod. However, there are also types of rear axles that allow the adjustment and setting of the rear wheel toe angle, see suspension.
Toe is measured and adjusted at the curb weight of the vehicle. It is checked during regular technical inspections (STK), or in case of service interventions such as replacing chassis parts or repairs after an accident. Toe can also be misaligned by hitting a pothole or during vehicle use. Therefore, it is good to check toe preventively.
Effects of Toe:
Toe is only one of many angles in the relatively complex wheel suspension geometry, which determines the driving characteristics of the vehicle. The overall suspension geometry is not the only factor affecting the final driving characteristics. Driving characteristics are also influenced by factors such as the vehicle’s center of gravity and the type of drive (front/rear), all of which affect the vehicle’s behavior on the road. Therefore, it cannot be generally stated that changing the toe angle will make an understeering vehicle oversteer and vice versa.
Toe affects three areas: 1 – stability in a straight line, 2 – handling when entering a curve, 3 – tire wear.
Stability in a Straight Line – increasing positive toe improves axle stability when driving in a straight line. Wheels with toe-in tend to return to a straight position, which ultimately increases driving stability at higher speeds. On the other hand, negative toe (toe-out) reduces stability and steering requires more frequent corrections.
Handling When Entering a Curve – increasing positive toe worsens steering response, and the vehicle is less willing to change direction, which can cause understeering when driving in curves. Conversely, increased negative toe improves vehicle agility and steering response. The vehicle more willingly changes direction, which can be advantageous in sporty driving or urban traffic.
Tire Wear – increased positive toe causes uneven tire wear, especially on the outer sides, because the tire slides more than it rolls. Conversely, increased negative toe causes wear, particularly on the inner sides of the tires.
In general, higher toe stabilizes straight driving at higher speeds, but on the other hand, the vehicle is less willing to turn. It is important to find the right balance of toe according to the driver’s preferences and the vehicle’s purpose. Sports vehicles may prefer slight negative toe for better handling, while family or highway vehicles will prefer positive toe for increased stability.
When to Check and Adjust Toe:
Symptoms of incorrect toe:
- excessive wear on the inner or outer sides of the tires
- tendency of the vehicle to pull to one side during acceleration and to the other side during braking
- tendency of the vehicle to pull to the right or left when driving at a constant speed on a straight road
- certain stiffness in the steering when turning
- poor steering wheel centering
- after passing through a curve, the wheels do not quickly return to a straight position
Remember: Incorrect toe adjustment causes rapid tire wear.
When to Check and Adjust Wheel Alignment:
Signs of Incorrect Wheel Alignment:
- excessive wear on the inner or outer side of tires
- vehicle pulls to one side during acceleration and to the opposite side during braking
- vehicle tends to drift right or left when driving at a constant speed on a straight road
- steering feels stiff when turning
- poor wheel alignment
- after turning, wheels do not quickly return to straight position
Remember: Improper wheel alignment causes rapid tire wear.
Did You Know:
- Due to the forces of rolling resistance acting on the wheels during driving, small lateral forces are generated in the steering mechanism. This prevents wheel oscillation that could be caused by play in the steering mechanism. Wheel alignment defines these tolerances, especially in older vehicles.
- Sports cars use slight rear wheel alignment to improve grip. Due to the slight misalignment, the tire has greater adhesion and can transfer more torque to the road. See graphs in the article on ABS. Sports cars utilize this for better power transfer to the road.
- Wheel alignment changes depending on suspension travel, for example, when crossing bumps, with vehicle loading, or during braking maneuvers. Braking forces also turn the front wheels towards misalignment, reducing straight-line stability, which is undesirable. Excessive alignment change due to wheel deflection negatively affects driving characteristics, which can change unexpectedly.
- Due to the forces of rolling resistance, the wheel tries to steer from alignment to misalignment. For vehicles with front-wheel drive, the forward-driving forces are significantly larger, pushing the wheels into alignment. To avoid worsening driving characteristics when lifting off the accelerator, these vehicles often use slight alignment.
- Do you know other important angles of suspension geometry? Read more here.
