From their website - "All our travel insurance policies will cover you for on-road motorcycling, with no cc restrictions, as long as you hold a FULL licence to be riding a bike of that size in your home country, and wear a crash helmet (even if local law doesn’t insist on it). On-road motorcycling does not necessarily have to be a tarmac road, but the road must be what passes for the road locally. (see below)"

They address the off-road question in some detail, check their website.