I have them on my 400 and I have the bigger tires, 18/8.50-8. I started out without tubes but have since switched because both sides developed slow leaks. I can only surmise the leak was at the bead because since I have had the tubes installed, I have not had to add air.Who runs tubes with their V61's? When I ordered mine this week Miller said these tires needed tubes. Just curious as to how people are running them. They are 16/6.50-8 on stock 300 series rims.