THEY call it the X factor, the metaphysical relationship a rider has with a bike.

Well, maybe it's actually the X and Y factor, X being the bike and Y being tyres.

Casey Stoner had a difficult but successful X relationship with his Ducati, and an even better Y one with Bridgestone tyres.
Valentino Rossi had a wonderful time on the Yamaha M1 scoring four MotoGP titles, and was able to muscle his way onto Bridgestones for 2008 when they were clearly the best rubber to have after earlier successes with Michelin.
It's worth revisiting Rossi's first encounter with the M1, for it provides a fascinating insight into how this mercurial rider needs to connect so deeply with his motorcycles. It is clear he has no real connection with his current steed, the Ducati.

Writing in his autobiography about the first day of testing the Yamaha M1, Rossi said, "That day in Sepang, 23 January, 2004, I stayed with my bike all afternoon and into the evening, well past sunset. I only left when it was dark. I just wanted to spend time with my new bike, checking and double checking that everything was in order. As I progressed from 125 to 250 then to 500 and onto MotoGP, I maintained that habit of dropping in at the garage at night.
I enjoy the bike during the day obviously, but my relationship with the bike is so special that I spend hours with it, just looking and admiring it, making sure that everything is in order.

"Those are very personal moments which I find difficult to describe. The Japanese guys, both the executives and also the engineers never knew this, not the guys at Honda, nor the ones at Yamaha. I don't think they'd really understand. They would probably view it as a waste of time, since I don't actually do anything concrete. I never touch anything to do with the bike itself, beyond obviously the stickers. And yet I find it hard to explain to an engineer that I enjoy simply being near the bike even when I'm not doing anything. It's a complicated concept to explain; the risk is that people will think that you're crazy." This is the X factor to the max.

With Rossi complaining about his Michelins in 2007 when Stoner was dominating on the Bridgestone-shod Ducati GP7, Dorna boss Carmelo Ezpeleta first floated the idea of a one-make tyre rule that caused quite a stir in the GP paddock. When Rossi demanded and received Bridgestones for 2008, the threat died down but was reignited by a blow torch when Dani Pedrosa made his controversial mid-season to the ’stones that set off massive ructions around the paddock. This was the final straw for Dorna and other key stakeholders.

The issue of tyres was threatening the integrity of the championship, making some of its biggest stars appear like petulant children wanting the same trick toy as the fast kid down the street.The easiest way to fix this mess was to make good on the 2007 threat to switch to a single make rule (which was originally a tactic to force Bridgestone to support Pedrosa and Rossi) and make it a reality so ending the bickering over rubber.
If Formula One and World Superbike can make a single brand work, why can't MotoGP? Like most things in life, however, the simplicity of a one tyre rule comes at a cost. Contrary to popular belief, Thomas Scholz, Bridgestone's head of logistics said that prior to the single-make rule, Bridgestone developed its tyres for each manufacturer but not individual riders.

He made the interesting comment that the Ducati GP8 worked the rear tyre less than the Yamaha, and that Rossi works the front tyre harder than Stoner so different tyres were made accordingly for each brand - that is not the case now. Fast forward to 2011, and an X + Y conversation between Kevin Schwantz and Rossi published on Superbikeplanet.com following his Valencia test on the Ducati GP12. It reveals Rossi's deep concerns with the single-tyre rule and the GP12, which he said was an improvement on the GP11, adding though, "We need a whole lot more than that." When Schwantz talked to him at Laguna Seca, Rossi said.
"I just cannot get any confidence from this bike. I can't get any feel from it. I cannot get what it is that I need to be able to push this bike to go quick.""We talked a little bit about Bridgestone," Schwantz wrote, and Rossi told me, "You ask the guys at Bridgestone, and they say 'this is exactly the same tyre we used last year. I just want to tell you one thing, Kevin. Same tyre? Bridgestone says same tyre.

In Malaysia in 2010, of the 17 or 18 bikes that were there, 90 percent of the guys ran the hard tyre. In 2011, there were 17 bikes on the grid, and all but one ran a soft tyre." Valentino said, "Almost identical weather. Not like, 'Oh, it was just about to rain,' or 'it was pretty cool.' No real difference as far as weather goes. And the only guy that ran a hard tyre was Simoncelli."Schwantz said, "My take on that is if the tyre's the same, why a complete flip from of all-hard last year to all-soft this year? "Most of the issues that seem to be hurting people are these tyres," Schwantz continued. "You talk to these riders about the first two laps, and it's just absolute fear. It takes time to get the things up to temperature and get a real feel for them. I don't know exactly what's going on there - have the bikes all gotten that much stiffer in the suspension? I have no idea if there've been that many changes in the bikes. But Valentino stared me straight in the face and said, 'Those tyres, they scare me.'"

– Darryl Flack