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Optimizing Rivian Tire Selection for Best Openpilot Autosteering Performance
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.
The core of the issue is that the steering system Openpilot currently uses for the Rivian is torque-based: it issues a torque command to the EPS (electric power steering) motor, and that torque is translated into a steering angle change, which then produces a lateral acceleration (m/s²). The relationship is mediated by the vehicle’s latAccelFactor — how much lateral acceleration results from a unit torque input.
Because latAccelFactor can vary widely between different vehicles (or even just different tire setups on the same vehicle), using a universal torque ceiling introduces a mismatch:
- High latAccelFactor setups: a moderate torque input already yields a large lateral acceleration. Such a vehicle may already be close to the safety ceiling (e.g., near 3.0 m/s²) with the current torque settings.
- Low latAccelFactor setups: the same torque input produces only modest lateral acceleration — the steering feels sluggish, even though the EPS motor has more margin to spare.
Because the system uses a single, universal maximum steering torque, you can’t raise that cap just for the low-latAccelFactor vehicles without risking that the high-latAccelFactor ones will exceed safety limits.
While the system does impose a universal torque ceiling, Rivian owners do have some degree of control over this limitation. By replacing their tires with models that provide a more favorable latAccelFactor (such as stiffer sidewalls or higher-performance compounds), drivers can effectively unlock more usable steering torque from the EPS. This tire choice can improve steering responsiveness within the same torque ceiling, reducing the underactuation experienced on less optimal setups.
| 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) |
- 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.
- Select tires with firm sidewalls and strong load ratings — Less flex means better steering control for Openpilot during lateral maneuvers.
- 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.
| 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) |
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.
| R1S/R1T | EPS P/N | Lat accel factor (m/s²) | Wheel Diameter | Tire | EV or E-rated |
|---|---|---|---|---|---|
| R1S | PT00001953-H | 2.8 | 22 | Continental TerrainContact HT | N |
| R1S | PT00001953-H | 2.7 | 22 | Michelin Defender LTX m/s2 | Y |
| R1S | PT00439050-D | 2.7 | 20 | Toyo Open Country AT III EV | Y |
| R1T | PT00001953-H | 2.7 | 20 | Cooper Discoverer ATP II | Y |
| R1S | PT00439050-D | 2.6 | 22 | Michelin Defender LTX m/s2 | Y |
| R1S | PT00439050-D | 2.6 | 20 | Goodyear Territory AT RIV | Y |
| R1S | PT00439050-D | 2.5 | 20 | Factory Pirellis | N |
| R1T | PT00001953-H | 2.5 | 20 | Michelin Defender LTX m/s2 | Y |
| R1T | PT00001953-G | 2.4 | 22 | Michelin Defender LTX m/s2 | Y |
| R1S | PT00781638-B | 2.4 | 22 | Pirelli Scorpion MS Electric | Y |
| R1T | PT00001953-H | 2.3 | 20 | BFGoodrich AT T/A KO3 | Y |
| R1T | PT00001953-H | 2.3 | 20 | Michelin Defender LTX m/s2 | Y |
| R1T | PT00001953-H | 2.2 | 20 | Toyo Open Country AT III EV | Y |
| R1T | PT00001953-H | 2.2 | 21 | Michelin Defender LTX m/s2 | Y |
| R1T | PT00001953-H | 2.1 | 20 | Goodyear Territory AT | N |
| R1T | PT00439050-D | 2.1 | 20 | Michelin Defender LTX m/s2 | Y |
| R1S | PT00781638-B | 2.0 | 20 | Goodyear Territory AT | N |
| R1T | PT00001953-G | 2.0 | 20 | Factory Pirellis | N |
| R1S | PT00001953-H | 2.0 | 21 | Factory Pirellis | N |
| R1S | PT00001953-H | 1.9 | 20 | Factory Pirellis | N |
| R1T | PT00001953-H | 1.9 | 20 | Factory Pirellis | N |
| R1T | PT00001953-H | 1.9 | 20 | Factory Pirellis | N |
| R1S | PT00439050-D | 1.9 | 22 | Factory Pirellis | N |
| R1T | PT00781638-B | 1.8 | 20 | Factory Pirellis | N |
| R1S | PT00001953-H | 1.7 | 22 | Factory Pirellis | N |
| R1T | PT00001953-H | 1.7 | 20 | General Grabber HTS60 | N |
| R1T | PT00001953-G | 1.7 | 20 | Factory Pirellis | N |
| R1T | PT00001953-H | 1.7 | 21 | Factory Pirellis | N |
| R1T | PT00439050-D | 1.6 | 21 | Factory Pirellis | N |
| R1T | PT00439050-D | 1.6 | 21 | Factory Pirellis | N |
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