Legal Question in Consumer Law in Oregon

It would be very difficult to legally require the dealer to replace the tires, if the dealer does not want to. Used cars and trucks are typically sold on an "as is" basis. The dealer would be responsible for fraud--for example, if the dealer actually knew that the tires were too wide and sold you the truck anyway without telling you about the tires. But no doubt the dealer would say he did not know that the tires were too wide.

Did you buy the truck with any warranty? Check the contract of sale and see what it says about warranties. It probably says there are none.

If the dealer refuses to replace the tires, you can legally picket the dealership. You can walk with a sign on the sidewalk in front of the dealership, noting your dissatisfaction. That may well result in a more reasonable attitude from the dealer. If the dealer calls the police on you, tell the police you are within your rights under the First Amendment and Article I, Section 8, of the Oregon Constitution. If you are arrested, then you can sue the dealer for causing your false arrest and seek damages. Much fun.