What reasons do Gramps and Sal's father give Sal for going on the trip? According to Sal, what are the real reasons? Why might the real reasons have been left unspoken?

In Walk Two Moons by Sharon Creech, Sal goes with her grandparents on a road trip that spans from Ohio to Idaho. Some of the reasons that are listed in chapter 2 include: 1) Gram and Gramps want to see Momma, who is resting peacefully in Lewiston, Idaho; 2) Gram and Gramps know that Sal wants to see Momma but is afraid to; and 3) Dad wants to be alone with the red-headed Margaret Cadaver. He has already seen Momma, and he did not take Sal. It is also stated by Sal's dad that she is being sent along to read maps, as Gram and Gramps don't know how.
As the story progresses, you learn more about the past travel experiences of Gram and Gramps that Sal hinted about early on in the novel. They were once stopped for driving on the shoulder instead of in the the designated lane. Readers also learn that they once stole the tires off a senator’s car in Washington, D.C. Also, Gramps once tried to help “a damsel in distress”—a lady who was having her own car trouble. He really thought he could fix the car, but he was unable to, and he actually made the problems worse by pulling parts away from the motor. The "damsel in distress" had to call a mechanic to get her car running again. As Sal thinks about it, all of the things that she has learned about her grandparents are good enough reasons for her to be on the trip out west.