Valentino Rossi's switch from Yamaha to Ducati may not have gone as smoothly as he might have hoped during winter testing, but it's not the biggest change the Italian has faced during his premier-class MotoGP career.

"500cc to 990cc was the biggest change for sure," Rossi told Crash.net. "But Yamaha to Ducati is a bigger change than from Honda to Yamaha, because the Honda and Yamaha were from some point of view more similar."

Rossi won the last 500cc title for Honda in 2001, which was his second year in the premier-class, then won the first 990cc titles for HRC in 2002 and 2003.

A switch to Yamaha brought further world championship success in 2004 and 2005. The Doctor then won two 800cc crowns for Yamaha in 2008 and 2009.

Prior to this year's team change, Rossi's last major technical overhaul was when he moved from Michelin to Bridgestone tyres for the 2008 season. It took Rossi four races to win.

Rossi and countryman Loris Capirossi are the only active MotoGP riders to have raced 500cc, 990cc and 800cc premier-class machines.

The MotoGP class is changing to 1000cc four-strokes for 2012 and Rossi's two-year Ducati deal means he will be part of the next era.