Auto tires are typically designed to be inflated to lbs. psi in the mid-to-low 30's. Bicycle tires typically 45 to 60 or 70 psi. What is it about the construction of the typical dirt bike tire that it is typically inflated to just 15 lbs psi? Do all dirt bike tire applications involve a tube? Why do bicycle tires require a tube & dirt bike tires, but not car or heavy truck tires? Is it because auto and truck rims are strong enough to withstand the pressure, but aluminum dirt bike rims can't? Why don't auto manufacturers reintroduce tubes into aluminum rims to save weight, or wouldn't aluminum casted rims be strong enough to support weight of car (they use alum. alloy now)? Why is a dent in rim of dirt bike tire important to avoid (from what I've read on this forum) if the rim does not have critical function of containing air pressure like an auto rim? What matter a dented rim?