Someone told me last week that tyres wider than 175 work LESS well on the Uno. There's just not enough mass for wide tyres.
Whether you believe that or not, I reckon that 195s are the go, there's a small amount of rubbing on the gearbox and it's really close with the struts. I agree with Morten that 7" wheels should be the max. Ideally, I suspect that 6.5" and 185 tyres would be the way to go.
But then again, I know someone who races on 175s (13") and gets much better times than anyone on wider tyres. So, looks vs. performance.
-Alex