After a lot of reading I have decided to give Pirelli's MT43 a go as a dual sport tyre. I ride mostly hardpack, gravel, rocks as well as street. I am currently using MT21's which have never given me a feeling of confidence, especially in turns. On the street they are downright dangerous when wet. As they are not available in Greece I am buing them online, probably from here: http://www.dirtbikebitz.com/pirelli-mt43-pro-trail-400-18r-p-4160.html My problem is Michelin Ultra Heavy Duty Tube selection. Tyre sizes are: 4.00 - 18 Rear 2.75 - 21 Front And available UHD tube sizes are: 18 100/100 Rear 18 110/100 Rear 18 120/90 Rear 18 130/80 Rear 21 80/100 Front 21 90/90 Front Thanks in advance for any replies!