I really like MT21s but have now moved on to Mitas as they are less expensive and harder wearing. Unfortunately MT21 are not the best in sand and I think the back tyre would be pretty much past it for the return trip.
I used to use them all the time on 650 sized bikes and they're good enough in the sand for what you'll want. Now I used tyres like Deseerts, E09s and 908s.
Front's vague in mud although they handle very well on tarmac but like ChasF says if you're riding there and back it'll be fecked so consider Mitas E09 certainly on the rear or more expensive, one of my favourites the Dunlop 908.
Ran one of these on the TAT trip i did a few years back, got 5k miles out of it and still had plenty of meat left when i got back (though not really enough to inspire confidence in english mud!).
Yes, I think it's perhaps one of the hardest wearing tyres that'll also perform well although as Losttheplot says, the rear tread pattern allows some lateral movement, perhaps far too much in mud but I like that in the dry.
I have a brand new 908 front which I'm not using if you find a rear and want to match them.
Ran one of these on the TAT trip i did a few years back, got 5k miles out of it and still had plenty of meat left when i got back (though not really enough to inspire confidence in english mud!).
Thanks Nathen do you remember me saying that my speedos gone up the creek well I can't seem to find anything wrong any ideaseverything else seems fine rides great.
If it's a mechanical speedo check the wheel gearbox is turning.
What about Heidenau K60 Scout tyres? 50-50 mud tarmac and long life - at least in 12GS sizes.