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 tells us 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.

Tire Characteristic	Effect on LatAccelFactor
Stiff or reinforced sidewalls (often EV-optimized tires)	Increases latAccelFactor
Soft, flexible sidewalls	Decreases latAccelFactor
Street/Highway tires (H/T, Touring)	Increases latAccelFactor (quicker steering response)
All-terrain/Mud-terrain tires	Decreases latAccelFactor (slower, softer steering)
Low rolling resistance	Increases latAccelFactor
Larger wheels (22")	Can slightly increase latAccelFactor (stiffer sidewalls)
Smaller wheels (20")	Can slightly decrease latAccelFactor (more sidewall flex)

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.
4. Opt for larger wheel sizes (22" preferred) — Bigger wheels reduce sidewall height, minimizing deflection and improving steering sharpness.
5. Choose street-focused tires (Highway Terrain or Touring All-Season) — These provide more precise response than off-road or all-terrain options.

Tires to Avoid if Prioritizing LatAccelFactor:

• Aggressive all-terrain (A/T) or mud-terrain (M/T) tires.

• Pirelli tires of any kind, even supposedly EV-rated, perform significantly worse than any other EV-rated tire we tested.

• Ultra-high-grip tires without stiff sidewalls.

Summary in Plain Terms:

If you want Openpilot on your Rivian to steer sharply and cleanly, pick smooth, tough street tires with big wheels and firm sidewalls. Look for EV or Touring tires and avoid chunky off-road ones.

Tire	Type	EV or E-Rated	Performance for Openpilot Steering
Continental TerrainContact H/T	Highway Terrain (All-Season)	No	Excellent — 2.8 m/s² (R1S)
Michelin Defender LTX M/S2	All-Season	Yes	Very Good — 2.3–2.7 m/s² (varies by config)
Toyo Open Country AT III EV	All-Terrain	Yes	Very Good — 2.2–2.7 m/s² (varies by config)
Cooper Discoverer ATP II	All-Terrain	Yes	Very Good — 2.7 m/s² (R1T)
BFGoodrich All-Terrain T/A KO3	All-Terrain	Yes	Moderate — 2.3 m/s² (R1T)

Quick Final Summary:

• Best LatAccelFactor = Street tires + Low friction + Stiff sidewalls + Big wheels.

• Worst LatAccelFactor = Off-road tires + High friction + Soft sidewalls + Smaller wheels.

Selecting the right tires is one of the simplest but most powerful ways to make Openpilot autosteering on your Rivian R1S or R1T perform better, feel sharper, and stay more predictable.

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.