Abstract: A test apparatus for measuring side-slip and gravity slip of a vehicle moving along a curved road or travelling across downhill. The test apparatus is adapted to be towed by a vehicle. The test apparatus is connected to a vehicle by a bar which has the other end connected to a vertically extending bushing which houses a pivot member extending perpendicularly to a riding surface. The lower end of the pivot member is connected pivotably to a wheel fork horizontally extending and supporting a test wheel in contact with a riding surface, while the other end of the pivot member extends out of the upper portion of the bushing and is connected by a horizontally extending level member which has the other end connected to a counterweight. An angle-measuring sensor is disposed over the upper end of the pivot member and is supported on a bracket secured to the upper end of the bushing.