The mobile robot doesn't reach to its max speed

edit

The youBot mobile robot is being used to test some kinematic controllers. There is a problem with the base not reaching the maximum speed. A maximum linear velocity of 1.5 is defined in the configuration file.

  type: steered_wheel_base_controller/SteeredWheelBaseController
      base_frame: base_footprint
      linear_speed_limit: 1.5
      linear_acceleration_limit: 2.5
      linear_deceleration_limit: 2.5
      yaw_speed_limit: 3.0
      yaw_acceleration_limit: 3.2
      yaw_deceleration_limit: 3.2

The maximum speed reported by Gazebo for the platform when I test it is 0.47 whereas the commanded linear velocity in x-axis is 2 and the rest is zero.

name: [ground_plane, youbot]
    pose:
       ...
    twist: 
      - 
        linear: 
          x: 0.0
          y: 0.0
          z: 0.0
        angular: 
          x: 0.0
          y: 0.0
          z: 0.0
      - 
        linear: 
          x: 0.475034689787  <----- current speed in x-axis direciton
          y: -0.00392167360465
          z: -0.0205054274451
        angular: 
          x: 5.50872400881e-06
          y: 0.000846332345603
          z: 7.43291489694e-05

There is no impact from increasing the PID's gains. The controller is a customised one called steerable_wheel_base_controller.cpp located in the same package. Any suggestions?

Melodic ROS, Gazebo 9, Ubuntu 18.04.