acceleration-field for unity3D racing game, c# - unity3d

Question

for a motorcycle racing game I want some parts of the track to increase the speed of the motorcycle.
I have a public float for the speed, which shows the speed in the inspector.
I added a plane with a Collider, which is a trigger and has the tag "speedfield"
Now I thought, some simple code, attached to the motorcyclescript below, would do it:
void OnTriggerEnter(Collider other)
{
if (other.gameObject.CompareTag ("speedfield")) {
Speed = Speed + 50;
}
}
But nothing happens. I think I'm missing something obvious here. Hope you can help! Greetings from germany :)
void FixedUpdate (){
Inputs();
Engine();
}
void Inputs (){
Speed = rigid.velocity.magnitude * 3.6f;
//Freezing rotation by Z axis.
transform.eulerAngles = new Vector3(transform.eulerAngles.x, transform.eulerAngles.y, 0);
//If crashed...
if(!crashed){
if(!changingGear)
motorInput = Input.GetAxis("Vertical");
else
motorInput = Mathf.Clamp(Input.GetAxis("Vertical"), -1, 0);
steerInput = Input.GetAxis("Horizontal");
}else{
motorInput = 0;
steerInput = 0;
}
//Reverse bool
if(motorInput < 0 && transform.InverseTransformDirection(rigid.velocity).z < 0)
reversing = true;
else
reversing = false;
}
void Engine (){
//Steer Limit.
SteerAngle = Mathf.Lerp(defsteerAngle, highSpeedSteerAngle, (Speed / highSpeedSteerAngleAtSpeed));
FrontWheelCollider.steerAngle = SteerAngle * steerInput;
//Engine RPM.
EngineRPM = Mathf.Clamp((((Mathf.Abs((FrontWheelCollider.rpm + RearWheelCollider.rpm)) * gearShiftRate) + MinEngineRPM)) / (currentGear + 1), MinEngineRPM, MaxEngineRPM);
// Applying Motor Torque.
if(Speed > maxSpeed){
RearWheelCollider.motorTorque = 0;
}else if(!reversing && !changingGear){
RearWheelCollider.motorTorque = EngineTorque * Mathf.Clamp(motorInput, 0f, 1f) * engineTorqueCurve[currentGear].Evaluate(Speed);
}
if(reversing){
if(Speed < 10){
RearWheelCollider.motorTorque = (EngineTorque * motorInput) / 5f;
}else{
RearWheelCollider.motorTorque = 0;
}
}
}

Answer 1

You overriding speed variable:
void FixedUpdate (){
Inputs();
Engine();
}
void Inputs (){
Speed = rigid.velocity.magnitude * 3.6f;
...
}
change it to:
[SerializeField] float speedMultiplier = 3.6f;
[SerializeField] float speedMultiplierChange = 2;
void Inputs (){
Speed = rigid.velocity.magnitude * speedMultiplier;
...
}
and
void OnTriggerEnter(Collider other)
{
if (other.gameObject.CompareTag ("speedfield")) {
speedMultiplier += speedMultiplierChange;
}
}

Answer 2

Make sure that all items in this checklist are satisfied:
The motorcycle has a Rigidbody component.
The plane doesn't have a Rigidbody component (it's useless and it could slow things down).
The Mesh Collider of the plane has Convex and isTrigger set to true.
The OnTriggerEnter method is in the motorcycle script.
The thickness of the plane trigger is wide enough: if the motorcycle speed is too high, it can pass thru the plane without the physics engine being able to register the trigger.
If this is the case, try to set the Collision Detection of the motorcycle Rigidbody to Continuous and/or decrease somewhat the Fixed Timestep in the Time project settings.
Most probably the problem is due to the last two bullet points.