Something like this should work:
http://www.screwfix.com/p/rawlplug-hollow-wall-anchors-m5-x-37mm-20-pack/99201?kpid=KINASEKPID&cm_mmc=GoogleLocal-_-Datafeed-_-Screws%2C%20Nails%20and%20Fixings&cm_mmc=Google-_-Product%20Listing%20Ads-_-Sales%20Tracking-_-sales%20tracking%20url&gclid=CPLE1uSrntECFYccGwod3jcJiw
You can get some from screwfix / homebase etc that are rated to 30 or 40 kg per fixing.
Are they like for radiators? That's what I had thought but wanted to check people with a better knowledge of these things!
Not sure about radiators but I used them in my last flat to hang some pretty heavy cupboards which didn't budge in the three years we lived there.
Assuming you run two or three down the vertical of each bike hanger, you'll have no issues.
@Tenderloin started
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Something like this should work:
http://www.screwfix.com/p/rawlplug-hollow-wall-anchors-m5-x-37mm-20-pack/99201?kpid=KINASEKPID&cm_mmc=GoogleLocal-_-Datafeed-_-Screws%2C%20Nails%20and%20Fixings&cm_mmc=Google-_-Product%20Listing%20Ads-_-Sales%20Tracking-_-sales%20tracking%20url&gclid=CPLE1uSrntECFYccGwod3jcJiw
You can get some from screwfix / homebase etc that are rated to 30 or 40 kg per fixing.