It could be a milk tanker, concrete mixer, refrigeration unit, stock transporter or logging truck.
Saturday will be a big day with the big trucks in Wanganui. Members of the Road Transport Association's Wanganui branch will be taking people for rides for $2 from Trafalgar Square to help Autism NZ.
Ride in a Truck Day is held every year and benefits a different charity each time. This year the Wanganui branch of Autism NZ will receive proceeds from the day.
Up to 30 trucks and drivers, all from the Wanganui region, will participate from 10am to 2pm.
Autism NZ Wanganui branch co-chairwoman Sue Kenny said it was a great venture, both in terms of raising money and children with autism being keen on taking a trip in the vehicles.
She said it may be "interesting" with some of the youngsters, given their sensory issues, but she says many boys with autism have a fascination with big trucks.
"It's a passion for them, so it's a great match," she said.
The money will help Autism NZ Wanganui branch projects and advocacy work, such as supporting parents accessing Government departments or assisting families at school meetings.
She said the branch also has a successful session for children with autism at the Boys' and Girls' Gym Club in Wanganui.
"It's really for all special needs children, and their friends and family. It's going very well."
However, swim lessons at the Splash Centre have been a bit more difficult to fund and organise, given a term of lessons costs about $120 per child.
"We would really like to be able to support parents there. It's very good for autistic children because the water is so calming."
The event has been organised by the Wanganui branch of the Road Transport Association, BP has come to the party, supplying $3000 in cash and $500 in fuel vouchers for the big trucks' big day.