Back when I was a newbie and decided to upgrade my drivetrain, another customer in the bike garage laughed at me. Why blew away so much cash for the new shiny drivetrain while keeping the shabby stock tyres? Honestly, I had no clue. I thought that the derailleur would improve the quality of a bike. He told me then, empathetically, that tyres are a lot cheaper, and will improve the ride quality better. It took me months until I swapped to kevlar-beaded aftermarket XC tyres, and I realized, he was spot on.