Hi Kevin, yes they are Marathon Supreme 50-599 (26 x 2 ), their actual width seems to be 49mm measured as accurately as I can. The wheels are XT hubs with Mavic 721 rims.
Hi Jags, on the few occasions I've been out in the rain they seem fine and haven't given me any problems so far on wet tarmac, I have nothing to compare them with though, they are the only tyres I have had on the Sherpa so far. The only 'interesting' incident was on dry roads when I hit a patch of dry sand and gravel on a corner at the bottom of a hill, bike went sideways about a foot before I caught her but I think any tyre would have done the same.
I should add that I have had one hawthorn through the tyre too, it got me home without knowing but was flat ten minutes after the ride.
For the winter I have been thinking of fitting some Marathon XR tyres, the roads and lanes round here can turn into a sea of mud in places and I'm not sure how the Supremes will handle that, so I'm looking at tyre reviews as well!
If you do go for the Supremes let us know how they compare, I and I'm sure many others would find the comparison of great interest.
Adrian