Always Get Same Physics Collision Rebound Force

I was working on a 3d car war game, and I was moving my cars through velocity using the following code:

 appliedSpeed += Time.fixedDeltaTime * 8f;
 appliedSpeed = Mathf.Min (appliedSpeed, speed);
 myRigidbody.velocity = transform.forward * appliedSpeed;

At collision time, I was giving backward force using the following code:

 private void ApplyReboundForce (Collision other)
     {
         Vector3 reboundDirection = other.contacts [0].point - transform.position;
         reboundDirection = -reboundDirection.normalized;
 //        myRigidbody.AddForce (reboundDirection * 7f, ForceMode.Impulse);
         myRigidbody.AddForce (reboundDirection * 180f, ForceMode.Force);
     }

But at present, I was getting a collision response force dynamically. Sometimes it was a higher force and sometimes it was lower force based on physics calculation. I want collision response force always same.

Here is the reference game for collision response force:
SUPER ADDICTIVE NEW .io Game | Bumper.io

I have already made all physics property of all cars same like physics material, rigidbody properties values etc... then also getting different collision response on each collision.

Please give me some suggestion to achieve something similar.