The sticker on the frame on mine says, "On road use only", and there isn't a whole lot of clearance left beyond the 28c Scwalbe Duranos that come stock. You might be able to get away with 32's but I'm a bit skeptical about that.
The Addict Gravel Disc might be a better option if you really plan on riding in gravel.
I just put Conti GP4000s on the Solace 20 Disc, the tire measured 31mm. Its is absurd what the tire makers do with its sizing accuracy. I would say at 31mm you could take the bike on gravel roads with GP4000s.
It's no problem, the stock 28mm Duranos are fine on gravel, but slip a little in loose gravel. They are road tires after all. No flats yet after 800km, I've done maybe 100km on gravel over a few different rides and they are holding up fine and the bike is actually fantastic on gravel roads.
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