Optimizing Rivian Tire Selection for Openpilot Autosteering Performance - commaai/openpilot GitHub Wiki
Background
In the context of Openpilot autosteering on Rivian vehicles (R1S and R1T), achieving a high latAccelFactor is critical for precise and responsive control.
LatAccelFactor (lateral acceleration factor) simply measures how easily the vehicle responds to a steering command:
Higher latAccelFactor = Rivian turns more quickly with less steering effort.
Lower latAccelFactor = Rivian requires more steering input to achieve the same amount of turning.
Tire choice, vehicle wheelbase, wheel size, and sidewall stiffness significantly impact latAccelFactor, even when the EPS (Electric Power Steering) system hardware is identical.
| Tire Characteristic | Effect on 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) |
| Stiff or reinforced sidewalls (often EV-optimized tires) | Increases latAccelFactor |
| Soft, flexible sidewalls | Decreases latAccelFactor |
Checklist for Choosing Tires to Maximize Openpilot Steering Performance on Your Rivian
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Choose street-focused tires (Highway Terrain or Touring All-Season).
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Prefer tires with low rolling resistance.
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Look for EV-rated or reinforced sidewall tires when possible.
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Opt for larger wheel sizes (22" wheels preferred if available).
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Select tires with firm sidewalls and good load ratings (E1 load rating helps but is not mandatory).
Tires to Avoid if Prioritizing LatAccelFactor:
Aggressive all-terrain (A/T) or mud-terrain (M/T) tires.
Ultra-high-grip tires without stiff sidewalls.
Tires paired with smaller 20" wheels or excessive sidewall flex.
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.
Good Example Tires from Rivian Testing:
Continental TerrainContact H/T
Michelin Defender LTX M/S2
Tires to Be Cautious About for High LatAccelFactor:
Factory Pirellis
General Grabber HTS60
Special Tire Notes:
Toyo Open Country AT III EV: This tire performs unusually well for an all-terrain option. On the R1S, it achieved a high latAccelFactor of 2.7 m/s², comparable to street tires. Its EV-rated design combined with its E1 load rating (stronger sidewalls) and moderate friction coefficient help maintain good steering response. On the R1T, however, latAccelFactor drops to 2.2 m/s², due in part to the R1T's longer wheelbase.
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 both 20" and 22" wheels on the R1T, demonstrating that a well-constructed tire can minimize the influence of wheel size on steering response.