Just put a set of
700x28c Vittoria randonneur Trekking/touring tyres on my Triban 500 (the orange one with steel forks £250. 30tpi double shielding. THe tyres got great reviews, hoping to go tour up to inverness from Glasgow before the weather turns too grotty.
I'd say there was about 4/5 mm clearance, hopefully will take the odd poly bag getting blown in to it.
There's no room for mudcards but I have a bontrager pannier that has kind of mud gard built in so I'm not worried about getting a muddy line up my back. I've been out to some gravel paths ( 1cm to 5cm crushed rocks over a nice flat dirt road) using the 700 Btwin Aero spoke wheels with some 23 tyres Hutchinson equinox 2's, really seemingly obvious bad idea, but i like to know for sure, the tyres side walls are obviously not made for this, and I soon tore a little hole in the side wall with a 20 pound pannier on the back hitting a little dink in the road with some sharp rocks in, someones gotta find out...
The pressure would have been 100psi, not much give. The second flat was because I fixed the flat without a pressure gage resulting in a snakebite pinchflat, after hitting another dink...
That said the wheels have held true even after a 6 mile walk over questionable roads with a floppy flat tyre on it , though definitely changing the back wheel for a 36 spoke. They are cheap, easy to true and
strong enough to handle the actual roads I'll tour on. I don't plan on having extra weight on the front apart from a liter bottle on the front downtube so I've kept the aero spoke wheel on, its seems stronger than the stock wheels that come with the bike, in the sense it's staying true and I've had it for far longer.
So aye, 700x28c Vittoria randonneur Trekking/touring tyres will fit the triban 500. I'll let you know if its 4/5mm of of clearance is a problem, but Touring isnt about bombing down hills at 40mph so I'm going with it.
Good luck