He smashed into a concrete wall. The other rider fell off, but was largely uninjured.
Mr Fothergill broke five ribs, some of them in multiple places. One lung was punctured, and his collarbone was broken. He also broke two vertebrae, one in his neck and one in his back.
His injuries would have been worse if he had not been wearing a lot of protective clothing, he said.
He was taken to Palmerston North Hospital by ambulance, x-rayed and scanned and made to lie flat until he had been assessed.
Doctors decided no surgery was needed, and he's been told he will make a full recovery. He's been up and walking, and was transferred to Whanganui Hospital on Thursday afternoon.
He was pleased with the change, and said Whanganui was a great hospital compared to other regional centres.
Doctors have predicted he may be in hospital for two to three months, but he said another week might see him recovered enough to leave.
"I'm not going to do anything silly. I just want to get better as quickly as possible without compromising anything."
He had really good people running his business and good support around him.
"So I don't need anything," he said.