$re = '/\b(A\d{1,8}|B|C|D|E|F|G|J|K|L|M|N|P|Q|R|S|T|U|H|V|W|Y|ZR)\b/';
$str = '225/75 R17.5 128/126М М470 Trans-Steel Semperit';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php