The Michelin website gives you a number that is "indexed" In other words a tire rated higher than the indexed number will be less fuel efficient. So if the Michelin is rated at 100, and a Continental is rated at 105, the Continental is 5% worse than the Michelin. Also if the number was 95 for instance, it would be 5% better in fuel economy. To calculate the true difference you would need the true rolling resistance coefficient. Check with a quality tire dealer, they can help