The 100 score is from the highest score on each tyre. As an example, if one tire stops at 4 meters and the other at 3 meters that is a 25% difference, one will get a score of 100 and the other a score of 75%. Obviously made up numbers to help you understand the basic principle of how tyre performance is compared. The comparison is so close other than wear, and Goodyear beats Michelin by a big margin. When choosing a tyre i suggest you look at premium tyres, Michelin, Goodyear Bridgestone, Pirelli etc. but others are also excellent you just have to do your own investigation of reviews online. There most modern premium tyres are mostly similar with differences you will not feel when driving.