The Night Wolves want to retrace the route of the Red Army in World War Two, and visit memorials to the Soviet troops who died fighting the Nazis.
But Poland's prime minister called the trip a provocation.
The bikers are renowned for their staunch support of President Putin, particularly his policies in Ukraine.
The US has put the club on its sanctions list.
The group heading for Berlin joined a large crowd at the Night Wolves' headquarters in Moscow on Saturday for the annual launch of the season.
Their leather jackets were newly embroidered: "Routes of Victory, 1941-45".
"I don't think visiting war graves is provocative or aggressive," one of the men, Vladimir, told the BBC as a rock band played on stage.
"Ours is a friendly visit, and we're unarmed. The most important thing is to visit the graves and do something to tell our grandchildren about."
Another biker already has a Polish visa and says he informed the embassy of his plans when he applied.
"So what basis does the Polish government have for denying me entry now?" Viktor Keller wanted to know.
The official reason is that the Polish authorities were not given sufficient notice of the trip and cannot guarantee the bikers' safety.
Russia's foreign ministry labelled that "a downright lie" and an "outrage".
But defiant statements aside, it remains unclear how the bikers can possibly reach the Reichstag by road now.
Their leader, known as "The Surgeon", suggested they may try to enter individually, via different crossing points. But even so, they could well be blocked at the border.
Now they have roared off towards Berlin, Russian state TV crews in tow, the Night Wolves will certainly cry foul if they are forced to return home.
But to Warsaw this war tour clearly symbolises a new era of muscle-flexing by Russia that makes it nervous.
An ultra-patriotic Russian bike club has begun a controversial ride to Berlin, even though Poland says it will not allow them to cross the country.