Unfortunately, there is no way to configure precisely what you are attempting. As kdisc98 mentions, the changes he lists are AP wide changes -- all SSIDs. It sounds like you have more than one SSID so this would not be ideal.
Another thing you can try, but is not exactly what you are looking for, is to set the "bikes" SSID to run on 2.4Ghz only. This will still do b / g / n in the 2.4Ghz band. Sometimes .11a and .11n issues , when running in 5Ghz, can be due to insufficient coverage (too few APs) as higher frequencies attenuate more rapidly than lower frequencies -- making this change may help validate this. To do this highlight the "bikes" SSID, select Edit > Click "Show Advanced Options" in the lower right corner > Set "Band" to 2.4Ghz only.