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As I said, I didn't look into it.
But I'd love to test 38c V 30c and see. I think at 22kmph the difference would be minimal.
skinny-
Sure (and you know this so I don't know why I am trying to explain it to you!) but the 38s are mainly comfortable because they are at lower pressure. But lower pressure means they will be slower on smooth road. If you pump up the 38s to the same pressure as the 30s they won't be any more comfortable. And hard to get decent-rolling tyres in big sizes - I have Marathons on my touring bike.
Maybe there is a sweet spot where you have it a bit lower to get the benefits and minimise the downside, or you could be clever with adjusting the pressures depending on surface, but I just hate stopping to pump up a tyre, or let air out for that matter, unless I absolutely have to - I would rather suffer discomfort from high pressures than do that.
frank9755
I won't go that big. I have that size on my touring bike which I have basically used as a mountain bike, ridden up mountain trails in Albania, down river beds in Wales, etc. But they are slower on the road. I don't think the terrain this year will be that bad - it's just 100km of gravel or whatever out of 4000km which will mostly be better than UK roads.