Saturday 5 March 2011: not merely curved, but actually bent
I have no record of what the original profile of my rear wheel's right rim was, though assume it to have been flat, perhaps lightly angled off-parallel with the left rim. The left rim has been lightly gouged to slight concavity by years of braking (in conjunction with the grinding-pastes deposited on the roads over the winter by the authorities) but the right (the inverse of the shape of the brake block, above) is somehow much worse despite being subject to the same conditions. All blocks have been replaced with softer-compound products to reduce further rim-wear until I can get a replacement emplaced. It's tricky to demonstrate the curvature of the rim by photographing the rim itself but after it's been replaced I'll maybe saw through it to see how thin it is at the gouge's apex.
A side-effect of such a worn rim and worn-to-fit brake block was that modulating the rear brake was almost impossible due to the block contacting the rim over the larger, curved area or not touching the rim at all; over the past few days the rear wheel was either moving or fully-braked, and as my weight moves forward when braking a fully-braked rear wheel was generally a locked wheel. I'd been using the front brake more to compensate but after it started squeaking earlier in the week (though I'd serendipitously ordered a nice new cable and outer just beforehand) I'd had to return to using the rear more and had thus had the rear wheel skid a couple of times. As I've not been anywhere too weird since I last inspected the tyres for little bits of embedded grit I hadn't re-inspected recently and therefore hadn't noticed that a couple of skids on the same bit of tyre had eaten through what remained of the outer rubber tread-layer of the tyre (which was also pre-emptively replaced at the start of the week but which requires a trip to Newbridge to collect), only noticing on Monday morning when I pumped the tyre up to head to work. I've a couple of worn-but-intact spares from when I changed them in June which will do for the next few days until the proper replacement can be collected.