FORMER 500cc World Champion Wayne Gardner has said Ben Spies' title-winning Yamaha YZF-R1 is the most difficult bike to ride on the WSB grid!

The 50-year-old Australian, who clinched the 500cc crown in 1987, made the synopsis after riding most of the World Superbike machines in a post-season test session at Portimao racetrack, Portugal.

Gardner, who was one of the few men to truly tame the vicious power of the bikes from the 500cc two-stroke era, heralded Spies' machine as the most difficult to ride around Portimao. The former Honda employee also tested a Ducati, Suzuki, BMW, Honda and Kawasaki.

Speaking after the test, Gardner said:

"They all have a different personalities and above all very particular characteristics. I was very impressed with the Yamaha but it's very difficult to ride. Congratulations to Ben Spies. He did a great job taking that bike to victory! "