Brandon Mark Christopher Hampson, 19, of Raven Street, Ribbleton, Preston, and accomplice Keaton Brooks, 19 of The Paddock, Fulwood, Preston, rained punches on the cyclist in front of horrified witnesses on Ribbleton Avenue in Preston.
He suffered a burst lip and a lump on his eye.
Preston's Sessions House Court heard William Murray was riding the bike at 4.50pm on July 19 last year when a BMW pulled up next to him and the defendants got out.
Brooks asked him where he had got his bike from because it "belonged to him".
Despite the victim's protests he punched him.
Hampson then joined in.
It was witnessed by a woman who described it as being "horrible to watch".
Both defendants pulled the bike away from Mr Murray and one cycled away on it.
In the early hours of the next day, the BMW was spotted at a garage forecourt. Both men were passengers in the car and were arrested.
The bike was recovered from Hampson's stepmother's home.
The court heard the bike was not Brooks' because the victim could prove he had it in 2017 with photographs.
In a victim impact statement he said he had often used the bike to take his daughter to nursery but was afraid to in case he saw them again.
He said he didn't ride it for month but in the end couldn't afford to take taxis everywhere.
he had attended his GP with anxiety and was struggling to sleep because he was "so worried these males would see him again".
Judge Andrew Jefferies QC said: " For no good reason you both punched an innocent man.
"It doesn't matter if you thought the bike was yours or not, you don't go round punching people in the face - it's a simple as that.
"You're both as bad as each other as far as your offending on this occasion is concerned."
Hampson who is already in jail for drug offences, was given six months to serve on top of his current sentence
But Brooks was given five months, suspended for 18 months, after the judge heard he had obtained work and was " showing signs of finally maturing."
He must pay the man £500 compensation.