Optimizing Rivian Tire Selection for Best Openpilot Autosteering Performance - commaai/openpilot GitHub Wiki

In the context of Openpilot autosteering on Rivian vehicles (R1S and R1T), achieving a high latAccelFactor is critical for precise and responsive control.

When Openpilot applies steering torque to the steering motor, the front wheels begin to turn, causing the vehicle to change direction. This change generates lateral acceleration — the sideways force you feel when cornering, measured in m/s², on a scale of 0 m/s² (minimum) to 3 m/s² (maximum) in order to adhere to ISO safety standards.

latAccelFactor gives us an estimate of how much lateral acceleration results from a given amount of steering torque.

• High latAccelFactor: The car responds quickly to torque. The EPS (Electronic Power Steering) needs to apply less force to achieve a sharp turn.
• Low latAccelFactor: The car responds slowly. The EPS must apply more force to produce the same turning effect.

1. Look for EV-rated or E1 load-rated tires — These are essential for optimal Openpilot autosteering performance and seem to be the factor that makes the most difference. Reinforced sidewalls handle EV weight and reduce flex, improving steering accuracy.
2. Select tires with firm sidewalls and strong load ratings — Less flex means better steering control for Openpilot during lateral maneuvers.
3. Prefer tires with low rolling resistance — Lower friction helps the vehicle respond more quickly to steering input.

Summary in Plain Terms:

If you want Openpilot on your Rivian to steer sharply and cleanly, tough tires with firm sidewalls. Look for EV or E-rated tires that are specifically built to support the weight of Electric Vehicles.

Important Factors Beyond Tires:

Wheelbase Effects:

• The Rivian R1S has a shorter wheelbase (~121 inches) compared to the R1T (~135 inches).

• A shorter wheelbase naturally allows the R1S to respond more quickly to steering commands, boosting latAccelFactor.

• Even with identical tires and EPS hardware, the R1S will show a higher latAccelFactor compared to the R1T simply due to basic vehicle physics.

This means some tire performance differences are not just about the tire itself but also about the underlying platform differences between the R1S and R1T.

Clarifying Wheel Size Effects:

• Larger wheels (22") can help by slightly stiffening the sidewall and reducing flex, but the effect on latAccelFactor is generally small.

• In practice, tire construction, sidewall stiffness, and friction characteristics have a much larger impact than wheel diameter alone.

• For example, the Michelin Defender LTX M/S2 showed identical latAccelFactors on 20", 21", and 22" wheels on the R1T, demonstrating that a well-constructed tire can minimize the influence of wheel size on steering response.