"As useful as an astray on a motorcycle” is another way of saying that something is not very useful. American stand-up comedian and actress Phyllis Diller (1917-2012) said in 1971:
“For me to go to the beauty parlor makes about as much sense as an ashtray on a motorcycle.”
In 1977, the line was also credited to professional comedy writer Robert Orben.
Wikipedia: Phyllis Diller
Phyllis Ada Driver (July 17, 1917 – August 20, 2012), better known as Phyllis Diller, was an American stand-up comedian, actress, singer, dancer, and voice artist, best known for her eccentric stage persona, her self-deprecating humor, her wild hair and clothes, and her exaggerated, cackling laugh.
15 August 1971, Corpus Christi (TX) Caller-Times, “Phyllis Diller—Tops of the put-downs” by Sam Lesner, TV sec., pg. 18, col. 1:
However, Phyllis’ old supper club comedy routine has come alive again with a fresh crop of zingy self-put-downs ("for me to go to the beauty parlor makes about as much sense as an ashtray on a motorcycle").
15 December 1971, The Plain Dealer (Cleveland, OH), “Open letter to Cosell” by Bob Dolgen, pg. 1-G, col. 7:
In fact, there’s a school of thought that holds that TV play-by-play men are as useful as an ashtray on a motorcycle.
24 June 1974, Chicago (IL) Tribune, “Phyllis Diller clowns it up at Lake Geneva” by Will Leonard, Te,po. sec. 2, pg. 13, col. 1:
But she (comedian Phyllis Diller—ed) still talks about ugly women, foam rubber padding, deodorants that have died, and trips to the beauty parlor that make “as much sense as an ashtray on a motorcycle.”
17 June 1977, Richmond (VA) Times-Dispatch, “Show Time” by Earl Wilson, pg. B-6, col. 2:
WISH I’D SAID THAT: Bob Orben’s simile: “As useless as an ashtray on a motorcycle.”
25 February 1980, The Age (Melbourne, Australia), “Letters to the editor,” pg. 10, col. 6:
Everyone knows the connection between cigarette smoking and lung diseases, and the repetition of this knowledge, especially to schoolchildren, is about as useful as. an ashtray on a motorcycle.
OCLC WorldCat record
Crazy like me
Author: Ray Scott
Publisher: Nashville, TN : Jethropolitan Records, 
Edition/Format: Music CD : CD audio : English
Ashtray on a motorcycle --
Stick Or Truth
You’re as useful as an ashtray on a motorcycle. #jokes
1:25 AM - 23 Jun 2016