Okay, here is the low-down on a trial run to the shops on my bike this evening ...
Shopping on a bike report!
I decided to give it a go. I got the rack out of my cellar, found some bolts the right size, plus various other bits and pieces, and fitted the rack to my singlespeed bike.
I have 2 panniers and both are fitted in the photograph above but thought I would only need one for today's shopping so I'd try that and see how it went.
I was a bit worried that my shopping would not all fit into the one pannier. It DID, but it was extremely heavy. When I unlocked the bike, I put the hefty lock in the pannier's side pocket. Having all of that weight on one side of the bike seriously unbalanced it. I had some iffy moments riding the off-balance bike home - trying to clip in in stop-start traffic, looking over my shoulder, and signalling were all very wobbly. I felt as though I was a novice rider again!
Here is a picture of the bike with its payload ...
When I got in I weighed the pannier and its contents (including the lock). It shocked me that it was 24 pounds - the bike only weighs 19 pounds! My advice - use 2 panniers for heavy loads and spread the weight evenly. In future, for lighter loads - a maximum total weight of (say) 15 pounds (shopping plus lock) - I would use one pannier again but bungee the heavy lock onto the opposite side of the rack to the pannier. Apart from anything else, those are very cheap panniers and I don't trust them with that much weight in. Having a clip break on a heavy pannier when riding in traffic could be a very scary experience!