How does a driver class rating of 51 effect my rating on an auto insurance policy?

This just sounds like your insurance company classification codes. These codes don't mean anything to you or anyone else except for the insurance carrier. Sometimes people get too iinvolved in what their code means and does this number or that letter make their insurance higher. Driver Class 51 could mean 25-64 year old married male drivers. Every driver on your insurance policy has a class cose. It's just ways of grouping certain individuals based on factors where they are similiar. They are nothing to worry about and nothing you can do anything about.