I like the Marathon Greenguard/classic but use it in 35mm and 38mm. My bicycle with the 35mm originally had 32mm Continental TopTouring tires, which I hated on gravel roads, which is why I went wider. On the bicycle which I'm more likely to encounter gravel roads on now (now, because it has better gearing), I have the 38mm. This bicycle rips on gravel.
So on your bicycle I would up the width to at least 35mm, if your frame/fork accommodates it.
Last edited by Nyah; 08-01-20 at 10:36 PM.