I noticed recently, but most notably while out tonight, that when I brake my bike pulls to the left. It tends to happen much more powerfully when I brake with my hands on the hoods, rather than in the drops. I've checked: Brake pad alignment - perfect Tyre pressures - perfect Shifters are at the same height - yep Stem is straight - yes I'm starting to wonder if maybe i have some oil or something on one side of my rims, or about my spokes perhaps not being tensioned properly. I can't take it into a bike shop, because I can't risk needing to spend any money on it. I am going to give it a thorough strip down and clean tomorrow, see if that helps, but has anyone else experienced this?