Police investigating the robbery today released e-fit images of two men they now want to identify.
The robbery happened close to the junction of Hey Street and Longside Lane between 6pm and 7pm on May 26 when a man approached a 15-year-old boy and demanded the bikes.
The man was then joined by two others and threats were made to stab the boy if he did not release the bikes.
No knife was seen, but the victim handed over both bikes.
One of the bikes was a Carrera Vengeance which is described as being black and silver. It had a bag under the seat and by the handlebars.
The other bike was a Carrera Sulcata and is described as being lime green in colour.
A police spokesman said officers wanted to hear from anyone who recognised either of the suspects featured in the e-fit images released.
One of the robbers had ginger hair and was described as being of muscular build and around 6ft.
The other was said to be around 5ft 8in and had hair which was described as being blonde or light brown.
Officers are also appealing for information about the Carrera Vengeance bike being taken from outside a newsagent in Great Horton Road at about 5.30pm the same day.
The victim said he had recovered the bike after pursuing the thief into Longside Lane where it was abandoned.
The suspect for the theft is believed to have run towards the city centre.
Anyone who can help the investigation is asked to contact Det Con 3128 Jewell at Bradford District CID on 101, quoting crime reference 13180254660, or use the live chat facility on the West Yorkshire Police website.
Information can also be reported anonymously to the independent charity Crimestoppers on 0800 555111.