They could be something that came with the bike, or something you bought afterwards. But what have you had on your bike that has made you think 'well, this is crap'. For me, it's the Yksion Elite tyres that came with my Road Pro Carbon SLR. In terms of 'performance' I can't see how they're any better than the Vittoria Zaffiro ones that came with the old bike. The main bug bear is the lack of seemingly any puncture protection. The bike they're on is my good one so I'm not riding it that often but I reckon about 1 puncture every 50 miles at least. What bike part has really wound you up?