Question HingeJoint2D prevents falling of a rigidbody2d

Hi, I'm using Hinge Joint 2D on a bike, to make it rotate around its pivot, but with this component, the body doesn't fall with gravity... how can I solve?

 

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class Controller : MonoBehaviour
6. {
7.     public float speed = 1500;
8.     public float rotationSpeed = 150;
9.  
10.     public WheelJoint2D backWheel;
11.     public HingeJoint2D body;
12.  
13.     private float movement = 0f;
14.     private float rotation = 0f;
15.  
16.  
17.  
18.  
19.     private void Update()
20.     {
21.         movement = Input.GetAxis("Vertical") * speed;
22.         rotation = Input.GetAxis("Horizontal") * rotationSpeed;
23.  
24.     }
25.  
26.     private void FixedUpdate()
27.     {
28.  
29.        
30.  
31.  
32.         if (movement == 0f)
33.         {
34.             backWheel.useMotor = false;
35.         }
36.         else
37.         {
38.             JointMotor2D motor = new JointMotor2D { motorSpeed = movement, maxMotorTorque = 10000 };
39.             backWheel.motor = motor;
40.            
41.  
42.  
43.         }
44.  
45.         JointMotor2D motorRotation = new JointMotor2D { motorSpeed = rotation, maxMotorTorque = 100000 };
46.         body.motor = motorRotation;
47.  
48.        
49.  
50.  
51.     }
52. }
53.  

I tried with this because the rotation is much smoother, I even tried transform.Rotate and AddTourque, but they won't represent a good rotation physics for a bike

 

I'll try to explain as easy as possible, I perfectly used a script to make the bike(or in your case the truck) go forward and backward(with up and down arrows), but I can't figure out a way to make the bike rotate(with left and right arrows).
I have a "public Rigidbody2D body" assigned to the body of the bike and then I tried to use something like:
body.transform.Rotate(0, 0, rotation); where rotation = Input.GetAxis("Horizontal") * rotationSpeed;

I even tried body.AddTorque(rotation); but the problem is that the rotation is not smooth, when the wheels are touching the ground, the rotation speed is fine, but when the bike is in the air, the rotation speed is insane.

 

I said that badly, the point of the question is about rotation of a bike, I wanted to try to rotate it with a HingeJoint, but as you said "A HingeJoint2D won't affect gravity" so I stopped using it and tried body.transform.Rotate(0, 0, rotation) or body.AddTorque.
I added maxAngularVelocity in order to keep the rotation of the body slower:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class Controller : MonoBehaviour
6. {
7.     public float speed = 1500;
8.     public float rotationSpeed = 150;
9.     public float maxAngularVelocity = 150;
10.  
11.     public WheelJoint2D backWheel;
12.     public Rigidbody2D body;
13.  
14.     private float movement = 0f;
15.     private float rotation = 0f;
16.  
17.  
18.  
19.  
20.     private void Update()
21.     {
22.         movement = Input.GetAxis("Vertical") * speed;
23.         rotation = Input.GetAxis("Horizontal") * rotationSpeed;
24.  
25.     }
26.  
27.     private void FixedUpdate()
28.     {
29.         if (movement == 0f)
30.         {
31.             backWheel.useMotor = false;
32.         }
33.         else
34.         {
35.             JointMotor2D motor = new JointMotor2D { motorSpeed = movement, maxMotorTorque = 10 };
36.             backWheel.motor = motor;
37.            
38.  
39.  
40.         }
41.  
42.      
43.         body.transform.Rotate(0, 0, -rotation);
44.                                                                             //body.AddTorque(-rotation);
45.        
46.  
47.        
48.         if (body.angularVelocity < -maxAngularVelocity) { body.angularVelocity = -maxAngularVelocity; }
49.         if (body.angularVelocity > maxAngularVelocity) { body.angularVelocity = maxAngularVelocity; }
50.  
51.  
52.     }
53.  
54.    
55. }
56.  

but now the problem is that the bike is shaking, even if I try to modify the value of speed, rotationspeed, maxAngularVelocity, mass of the objects