I’m working on a constraint-based vehicle chassis and using the ball variant of Parts to simulate tire traction. While testing, I observed that friction simulation seems to vary depending on the direction of acceleration. Specifically:
- At “cardinal” directions relative to world, (0°, 90°, etc.) the wheels simulate less friction
- At “intercardinal” directions (45°, 135°, etc.) the wheels simulate more friction
I recreated this behavior on a simplified chassis in a new file.
Place Setup: The chassis takes a friction value (in the bottom left) and adjusts the wheels’ CustomPhysicalProperties accordingly. It tests for a 0-50 time, the angle at which acceleration began, and the ratio of wheel speed to car velocity, or wheelspin (shown in output window). For example, 1 means that the speed calculated by wheel rotations is the same as the chassis’ actual velocity, 2 means that the wheel speed is twice as high as the actual velocity (wheelspin). This wheelspin measurement is meant to demonstrate how tire friction interacts with surfaces.
Case 1 (Intended Behavior/Cardinal Directions): There is some wheelspin as the chassis accelerates (the wheelspin ratio is significantly above 1) until the vehicle reaches its max speed.
Case 2 (Alternate Behavior/Intercardinal Directions): The wheelspin ratio stays relatively close to 1, indicating no wheelspin. The 0-50 time is also ~0.4s less. Setting the tire friction value to 1 results in the chassis behaving similarly in all directions.
Here’s the repro file:
frictiontest.rbxl (76.1 KB)
Here’s a link to the original post that I made in June which has some additional information.