His father Graeme has since painted an image of his son on two of his bikes, as well as phone numbers and websites that offer help, such as depression.org.nz.

"There is plenty of help available for this terrible illness that claims more lives every year than our roads, but nobody seems willing to talk about it. Until we change this, there isn't much chance of the statistics improving," he said.

Mr Billington, who lived in Palmerston North for 22 years, has twice raced at Manfeild with the bike, and last weekend took it to Taupo. He will be back at Manfeild in April.

Now Mr Billington lives in Tauranga, so was not always around while his son battled his illness.

"[Paul's death] was completely out of the blue for me. Because he's 500 kilometres away I didn't get to see him that regularly.

"I guess, looking back, I probably should have looked more into what was going on in his life."

Mr Billington said there were signs his son wasn't quite right when the pair travelled to the South Island to compete in the NZ superbikes championship.

It is these signs, such as changes in behaviour and out-of-character aggression, that Mr Billington is trying to raise awareness of.

"There's nothing I can do to change what's happened to us. All I can really do is try to stop it happening to other people."

Before Mr Billington first raced one of the bikes at Manfeild, Paul's friends signed it.

"My advice is, if you know somebody who suddenly starts to have mood swings or shows any of the signs connected with depression, don't just walk away, do something.

"If you're still concerned, call the crisis team at your local district health board."

If you are worried about family or friends, you can call suicide helpline 0508 tautoko.