Michael Davidson, of Arbroath, was working for Angus Tyres Ltd trying to replace four wheels on the tractor when the accident happened at a farm near Carnoustie on November 12, 2012. He was trying to protect another farm worker from the wheel as it came off the studs, but was knocked to the ground.
He was taken to hospital with a collapsed lung, fractured ribs, a broken leg and broken collarbones. He needed two operations and was off work for seven months while he recovered.
The Health and Safety Executive launched an investigation and found several failures by the company, which had not given any training to employees to ensure they would be able to change tractor wheels safely. Workers were left to change wheels alone, despite them weighing up to half a tonne, and no risk assessments or manual handling assessments had been done.
Angus Tyres Ltd, of Hill Place, Arbroath, was fined £10,000 after pleading guilty to breaching the Health and Safety at Work etc Act 1974.
HSE Inspector Michelle Gillies said: "It was entirely foreseeable tractor wheels would be heavy and difficult for one person to handle alone. They can quickly become unstable and aside from the danger of crush injuries that resulted in this case, people working with wheels of such a weight are exposed to strain injuries.
"The task being undertaken by Mr Davidson was not an unusual one and the risks are well recognised in the trade but the way the work was being carried out was inherently unsafe. Angus Tyres Ltd should have properly assessed the risks in advance to determine the correct equipment and training needed to change the wheels safely."