So, I have had to make quite a few (expensive!) changes to my (supposedly cheap) single-speed commuter bike since posting here.
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Firstly the gearing was too high for me. It was a 48t (tooth) front and 17t rear cog. I sent it in the first time round and took a few teeth off the front. Sadly, the original chain didn't fit the new cog(!) so I needed a new chain as well. End result: 46t front, 17t rear. Shiny new single-speed chain.
Next problem was the super-wide cyclo-cross tyres the previous owner had fitted. Yes, they were comfy going over the lumps and bumps but the clearance was roughly 1mm between the tyres and the brakes/frame so there was no chance of getting a mudguard in there. It's a shame I didn't notice this when I first bought the bike. I could have opted for the crud catcher ones but they are not so good really. If it is a commuter bike, it has to have proper mudguards.
So I got busy on eBay and got a set of shiny new single speed wheels from here. Then I took it to the "local" bike shop and had them fitted with Gator Skin 4 season tyres and some proper SKS mudguards. All the work was done at The Bicycle Works who I thoroughly recommend.
I haven't had a good shot on it so far but on the ride back from the shop I could really notice how much better rolling the bike was. It is now much easier to pedal. And because the tyres are so much smaller (25c compared to the 35c on it originally), I don't have a problem with toe strike on the front wheel anymore. Looking forward to more commuting on it.
And I got a fixed-cog with the wheels which is fitted to the non-drive side of the rear wheel. I have the option of running the bike as a true fixie if I wish. Maybe I will give it a try once it gets warmer...
Anyway, the picture shows the end result. A bike now fully capable of commuting throughout the year. Except when it snows :-)