Override mage2 core class

di.xml

<?xml version="1.0" ?>
<config>
  <preference for="Magento\Catalog\Block\Adminhtml\Product\Edit\Tabs" type="Namespace\Spareparts\Block\Adminhtml\Product\Edit\Tabs" />
</config>

Tabs.php

<?php
/**
 * Copyright © 2016 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */

namespace Namespace\Spareparts\Block\Adminhtml\Product\Edit;

/**
 * Admin product edit tabs
 * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
 */
class Tabs extends \Magento\Catalog\Block\Adminhtml\Product\Edit\Tabs
{

    /**
     * @return $this
     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
     * @SuppressWarnings(PHPMD.NPathComplexity)
     * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
     */
    protected function _prepareLayout()
    {

        $this->addTab(
            'spareparts',
            [
                'label' => __('Spareparts'),
                'url' => $this->getUrl('catalog/*/spareparts', ['_current' => true]),
                'class' => 'ajax',
                'group_code' => self::ADVANCED_TAB_GROUP_CODE
            ]
        );
        parent::_prepareLayout();


    }

}