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@gbj_tester
20c on the front for the aero, 23c on the back for the low rolling resistance. And 35c (actually 38mm wide) on the "commuter", not that I commute but it's the bike I'd use if I did.
It's been said a million times before, but Ed is half right. Wider tyres have lower rolling resistance all other things being equal. By leaving out that caveat, Ed exposes himself to flak from nit-pickers who can point to examples of 1kg 2.5" DH tyres which don't roll as fast at 2 bar as a Veloflex Record 20c rolls at 10 bar. Arguments about extra weight of bigger tyres are spurious, since very few rides have a terrain where the weight isn't easily countered by the lower rolling resistance. On a commuter bike where the tyre probably doesn't have any significant interaction with the rim as far as air flow goes, switching up from 25c to 35c adds about 0.007m² to the CdA, out of a total which is likely to be around 0.4m², i.e less than 2% extra aero drag
Plug the numbers into the calculator and we can see that at 25km/h, tyres 10mm wider which weighed 500g more for the pair would still save power as long as they had 10% less rolling resistance. AFM tyre tests show >10% drop in Crr switching from 23c to 25c versions of the same tyre in some cases, so there seems to be scope for adding some protection and lowering pressure and still getting a 35c to outroll a 25c by enough at commuting speeds to make it faster overall.