Organisers of the Oroua Downs trail bike ride plan to change the course after injuries marred this year's event.

The ride, held on Sunday, was organised by Oroua Downs School and Foxton Rotary and covers 40 kilometres of hilly paddock, sand country and forest.

Organiser Bruce Jack said the track was drier than normal, which had an adverse effect on the riding conditions.

A 13-year-old girl had to be airlifted to hospital by the Palmerston North rescue helicopter after she fell off her bike. Two other riders were taken to hospital with moderate and minor injuries, which included a broken leg.

The 13-year-old girl was in a stable condition in Palmerston North Hospital.

Mr Jack said he was yet to find out why the 13-year-old girl fell, but said the man who broke his leg was going too fast and trying to overtake when he hit a tree.

"It was drier and faster and because it was dry the ground turned to powder," Mr Jack said."The guys were just going too fast."

He said the track was normally wet and muddy.

Most riders were travelling safely, but a few of the 500 people involved were not. "The guys that were doing it, were doing some dumb things, really."

Some of the other injuries may have been caused by clipping trees in the forest, he said.

Mr Jack said organisers would look at the track and make alterations to problems areas for next year's ride.

"We'll change the track around here and there," he said.

- © Fairfax NZ News