Its a too complicated a subject to cover over in a web site.

Beyer has writen 2 books to explain it all.

Try Amazon.com his books are available and at a reasonable price. Save yourself some time and order all of them at once if you are really serious about doing speed ratings.

Also remember the amount of work involved setting up the database and par times.

After that its fairly simple.

I know this does not answer your question, however in reality it cannot be answered as simply as you might think.

Regards

Michal