Jamaican 100 metres world record holder Asafa Powell is not the world's best sprinter, retired 200 and 400 record holder Michael Johnson said.

That honour, he said, goes to American world champion Tyson Gay. "I measure sprinters based on consistency and (Gay) is the more consistent," Johnson said during an online chat on the International Association of Athletics Federations (IAAF) website (www.iaaf.org).

"He's got better performances at championships," Johnson added of Gay, the world 100 and 200 metres champion. “Asafa Powell is a great talent but he can never get it done. He's failed time after time at the championships."

Powell's world record of 9.74 seconds is a 10th of a second faster than Gay's best of 9.84 but the Jamaican has never won a global sprint title. That will not change in Beijing, according to Johnson.

Asked by an online questioner how Powell could win 100 metres gold at the Beijing Games in August, Johnson replied jokingly: "Trip Tyson Gay."

Johnson also predicted Gay would win the 200 in Beijing to match his 2007 World Championship sprint double. Gay will test his 200 metres speed for the first time this season  at the Jamaican International meeting in Kingston.