Steve I can confirm they definitely do fit 28mm tyres.... I have got some but I have just taken them off 'cos I think they rattle. Not on perfectly smooth road, but on any surface imperfection of more than about half an inch they rattle.
I think they I fitted them completely correctly and everything was tightened up but I think it's just the nature of the stays, I think it's the bit where the outer bit of the stay is held onto the inner bit using a grub screw that is rattling. I did replace one of the grub screws with a similar (but slightly shorter) one because I rounded the original one but that isn't an issue, that's on the front one and it's the rear that rattles.
I am going to fit some Tortec reflector guards instead, see how they go on. They have got 'normal' stays but are a bit thicker than Chromoplastics so should be able to hold a light without cracking.
You can have my PDW ones for half RRP if you like, I have got a box that they will fit in to post them. If I haven't put you off
Edit: ah - sorry, I cannot attest to how well they will fit under calliper brakes as I have got discs. They do come with some metal mounting plates which look like they're designed for the purpose of going over the caliper though.
I'm quite happy to send you them to try if you want for just the cost of postage - if they don't fit or the rattle annoys you then you could ebay them and pass on what you get minus a cut?
