The government is under pressure to rethink its new motorcycle test following a series of crashes in the first few weeks of its use.
Some instructors blame a new "swerve test", which they say is dangerous - particularly in the wet.
Bikers say it could be difficult to safely achieve the 50km/h speed the manoeuvre required.
The Driving Standards Agency (DSA) said the test was needed to help reduce deaths of motorcyclists on the roads.
It said the test was designed by professionals in conjunction with the motorcycle industry and 300 trials were carried out before it was brought in.
During the test, learners have to reach 50km/h (31.2mph), then perform a swerve, on special test centre tracks.
"A brake and swerve manoeuvre on a wet road is fraught with danger for even an experienced motorcyclist"Jeff Stone
British Motorcyclists Federation
But some instructors say that if riders brake and swerve at the same time they are likely to come off, particularly in the wet.
The new test was brought in at the end of April and in the first three and a half weeks there were 15 incidents during the exam, with at least one rider left with broken bones.
The Motorcycle Action Group says it has warned the government that the test is unsafe and asked for changes.
Its national chairman, Paul Turner, said the new test had been brought in without enough consultation or consideration for riders.
"We don't mind improvements in the test which will make for better riders, but putting people at risk during the test is ludicrous."
He said the new test had been very poorly implemented as many test centres were not ready, and the number of centres had been reduced from 200 to 60.
Jeff Stone, of the British Motorcyclists Federation, said: "There is no real argument with the actual test, but the DSA really do have to take note of 'real world' conditions.
"A brake and swerve manoeuvre on a wet road is fraught with danger for even an experienced motorcyclist, so there needs to be a safer option for inclement weather conditions."
Mr Stone pointed out that car driving tests were postponed in snowy or icy conditions.
"A motorcyclist's competency can be best judged in the dry," he said. "Wet conditions introduce a chance element that should not be part of the test."Unsafe acceleration?
Phil Woolley, 28, of Liverpool, recently failed his test after completing the swerve slightly below the required 50km/h.
But the size of test centre sites made it difficult to reach the speed without accelerating unsafely, he said.
"Do it at a controlled speed and you will almost certainly fail," he said. "Or you just floor it as hard as you can and there is a good chance you will pass, but also a risk you will come off."
The hazard avoidance manoeuvre was the only part of the test he had failed, Mr Woolley said.
"I know I can ride a bike, so it's frustrating," he said.
Barry Kenward, deputy chairman of the Driving Instructors Democratic Union, has put in a Freedom of Information request to find out how many accidents have occurred on the test so far.
He said: "In the dry the test is fine but the stopping distance is not enough for the stop to be carried out safely when it is wet.
"I have been riding for 30 years and I would not want to do the test they have to do."