This is the second post in two part series called 'Tires and Formula One'.  The introductory part is here.  
While tires have traditionally played a very important part in any kind of motor sports, tires have never been solely responsible for swinging race results, one way or the other, in Formula One, or at least, till not too long ago.  As explained in the introductory post,  tire choices are very crucial, but they only were critical in changing weather conditions.  They were largely predictable otherwise. Also,  Formula One tires were built to last long.  Indeed in the controversial 2005 season,  cars had to run the same set of tires from start of the race to the finish, but we are getting ahead of ourselves.

Prior to 2006,  there were primarily two main tire suppliers for Formula One teams: Michelin and Bridgestone.  Some teams went the Bridgestone way while others went with Michelin. There were tracks where Bridgestone tires performed better while Michelin had the upper edge on other track surfaces, but they both made tires that lasted.  Pit stops were seldom made for tire changes only.  Drivers pitted for fuel and fresh tires were slapped on each time they stopped for fuel, as it took less time to change tires than refuel the car.  The fueling rate in Formula One was 12 litres per second and cars routinely fueled up as many as 80-120 litres of fuel in one go, meaning stationary time of 5 to 10 seconds, which was more than enough to change the tires.  Drivers rarely wore their tires out before they needed to stop for fuel and the only time when the tires necessitated the stops were when they got punctured or badly flat-spotted and those were rare incidents.  

Cut to 2005, the governing body of F1, FIA mandated that cars will no longer make tire changes during the race.  That is, cars had to complete the races on the same tires they started with,  unless they were punctured or flat-spotted to the extent deemed unsafe. This rule was introduced with the intention of cutting costs to benefit teams which did not have pockets that ran deep enough.  In hindsight, it was one of the most disastrous rule changes ever brought in by FIA.  While Bridgestone and Michelin both manufactured excellent tires,  it's too much to expect a set of tires to last the entire race distance in a typical Formula One race.  Indeed, it made racing risky.  So much so that Michelin issued a safety directive which stated that it was unsafe to use their tires for the United States Grand Prix, if the track layout was not modified.  The layout was not modified prompting all cars running Michelin tires (all but six on the grid) to retire after the formation lap was completed, thereby not even completing a single lap of the race.  Read 'The United States GP fiasco'  for details. This caused a huge furore and and the next year saw FIA reinstating mid-race tire changes, while limiting the maximum number of sets of tires a team could use over the weekend.  Also, Bridgestone was appointed the sole tire supplier for all teams in Formula One. With the advent of single tire vendor,  all teams had exactly the same tire options available.  This leveled the playing field further and put the focus back on drivers' skill and the cars themselves.  All seemed to be well until Bridgestone announced their decision to exit Formula One at the end of the 2010 session.  FIA announced Pirelli as the replacement for Bridgestone.

How Pirelli has been killing the sport as we know it:

How? Simply because in the past year and a half that they've been around, they've proved that they are utterly incapable of manufacturing tires that last.  Combined with FIA's restrictions on the number of sets of tires a team can use over a race weekend, this has led to disastrous consequences.  The Pirelli P Zero tires get shredded to bits in no time and teams don't have the luxury of changing them, forcing drivers to run their cars progressively slower.  Races are now a war of attrition: you bide your time while your opponent wears his tires out doing what Formula One is all about: driving fast.  The cars which run slower then lay in wait and attack at the end when their opponents have vastly degraded tires. This is NOT real Formula One racing.
Pirelli management claims that their rapidly deteriorating tires make for a more interesting and suspense-filled race. That is like saying match fixing makes cricket more interesting!   Drivers put in a fast lap and their racing directors get on radio immediately, telling them to watch their tire wear.  Sebastian Vettel secured the fastest lap in the middle of the European GP prompting commentators to ask why he was driving so fast! Formula One races have now stopped being a competition in which cars try to go faster than anybody else.  They now are about cars going as slow as they possibly can, while still staying ahead of others.  The races are no longer about the drivers and their cars.  It's about tire poker.  Take the race in Valencia, this year.  Fernando Alonso who was winning was pretty nervous as his tires were almost completely destroyed. The only reason why he won was because his main competitors were also battling similar problems.  In contrast,  Michael Schumacher and Mark Webber, who made late stops for fresh tires were suddenly overtaking everybody on track, simply on account of being on fresher tires. Both had elected to bide their time, driving slower than others on shot up tires before making their late tire changes, and both would have passed a helpless Alonso if the race had a few more laps remaining.  If driving slower for most of the race is the strategy to finishing better, I think Formula One as we know it is dying a slow death.  FIA has been making change after disastrous change and now Pirelli seem to be driving in the last nail in the coffin of a sport we've known and loved as the pinnacle of motorsports.