Eighteen motorcyclists have died in the two force areas covering Dyfed-Powys and North Wales Police, compared with eight in 2013.
North Wales Chief Constable Mark Polin said the good weather had brought out more bikers with a minority seeking to "abuse our roads through excess speed".
Road safety charity Brake wants the 60mph limit on rural roads to be cut.
The Dyfed-Powys Police area has had 11 fatalities between January and September this year compared with four in 2013.
Figures for north Wales show there have been seven fatal bike crashes this year with four in 2013.
Also, 85 bikers have been seriously injured in north Wales this year compared with 55 in 2013.
Mr Polin, who rides a police motorbike, told BBC Radio Wales' Country Focus programme that rider error was a big factor in many accidents although other motorists also played a part in other incidents.
He said the force was trying to tackle the problem with education, including using a scheme called BikeSafe which helps and advises motorcyclists, as well as targeting those who speed.
"There is a minority who quite clearly seek to abuse our roads through excess speed," he said.
"Our approach is, for those who do not ride safely and break the law, then, of course, we will seek to identify and prosecute them."
Brake campaigns officer Ed Morrow said a survey this summer showed one in three motorists admitted to speeding on rural roads.
"There is a problem here that we have speed limits of 60mph on many country roads and that is just far too fast for safety when you think about the unexpected hazards that you get on these roads," he said.
Fatal motorcycle accidents in parts of rural Wales have increased dramatically compared with last year, figures show.