The problem is with the rig as well, you need to make sure the wheels are rotating in the right direction.
I recommend putting a texture on the wheels so you know what direction it is going, and add a negative sign to reverse the direction if needed.
seat:GetPropertyChangedSignal("Throttle"):Connect(function()
frontleft.Wales.WheelConst.AngularVelocity = speed*seat.Throttle
frontright.Wales.WheelConst.AngularVelocity = speed*seat.Throttle
backleft.Wales.WheelConst.AngularVelocity = -speed*seat.Throttle
backright.Wales.WheelConst.AngularVelocity = -speed*seat.Throttle
end)
List for more tutorials with a lot more to learn: