Thirteen drivers faced the court in the western city of Rennes along with their boss, 42-year-old Silviu Pietroanu, who received the longest sentence.
One of their lawyers, Sabrina Baudet, said they would appeal.
During their breaks they stole wheels and syphoned off petrol, usually from lorry parks on industrial estates.
They then sold the wheels in Romania for 250-300 euros each, the equivalent of their monthly wages, according to public prosecutor Arnaud Marie.
The illegal trade allowed them to earn five times their income.
Investigators identified 80 such thefts worth 676,000 euros between November 2013 and November 2016.
Pietrosanu, who was accused of aiding and abetting by keeping silent, admitted knowing about the scheme.
"I let them do it to keep them," he told the court. "I was happy with their work."
The perpetrators, who were found when police tracked their mobile phones to the crime scenes, confessed when they were caught.
"These people's living conditions really are very difficult," defence lawyer Bénédicte Gosselin pleaded, pointing out that there were not guilty of any violence.
Several of the accused have been accused of same crimes in Germany, Austria and Belgium, where Pietrosanu was convicted of similar offences in 2012.