Related Products Slider

Hey, I have a problem with the “Related Products”-Slider on the buttom of my product pages. Example: I have a main category “Bikes” in my shop, which is grouped in different sup-categories like Mountainbikes, Roadbikes, Trekkingbikes….etc. If I create a new Roadbike for example, the slider displays all products from the main category “Bikes” but I want to display automatically only the Roadbikes as related products. Not a Mountainbike or a Trekkinbike. That doesn′t make any sense.
What code do I have to change ? Should be in the related.php file (see code bellow), but I haven′t any experience in reading / changing codes.
Or is there any Plug-In you can recommend?

$related = $product->get_related( $posts_per_page );

if ( sizeof( $related ) == 0 ) return;

$args = apply_filters( ‘woocommerce_related_products_args’, array(
‘post_type’ => ‘product’,
‘ignore_sticky_posts’ => 1,
‘no_found_rows’ => 1,
‘posts_per_page’ => $posts_per_page,
‘orderby’ => $orderby,
‘post__in’ => $related,
‘post__not_in’ => array( $product->id )
) );

$products = new WP_Query( $args );

$woocommerce_loop[‘columns’] = $columns;

if ( $products->have_posts() ) : ?>

<div class=”related products”>

<h2><?php _e( ‘Related Products’, ‘i-craft’ ); ?></h2>

<?php woocommerce_product_loop_start(); ?>

<?php while ( $products->have_posts() ) : $products->the_post(); ?>

<?php wc_get_template_part( ‘content’, ‘product’ ); ?>

<?php endwhile; // end of the loop. ?>

<?php woocommerce_product_loop_end(); ?>

</div>

<?php endif;

wp_reset_postdata();