Change posts per page for post type

gistfile1.aw

<?php
/**
 * Change 'products' posts per page on archive
 * This is the long version that explains everything
 */

function be_modify_products_query_long ( $query ) {
	// Check to make sure we're modifying the main query
	global $wp_the_query;
	if( $wp_the_query !== $query )
		return;

	// Make sure we're not in the admin area
	if( is_admin() )
		return;

	// Make sure we are on the post type archive query
	if( is_post_type_archive( 'products' ) ) {
		$query->set( 'posts_per_page', '8');
	}
}

/**
 * Change 'products' posts per page on archive
 * This is the short version we actually use
 */

function be_modify_products_query( $query ) {
	global $wp_the_query;
	if( $wp_the_query === $query && !is_admin() && is_post_type_archive( 'products' )
		$query->set( 'posts_per_page', '8' );
}

add_action( 'pre_get_posts', 'be_modify_products_query' );