The Quick Flate four-way system — inflate and deflate all four tires at once.

This is the full version: hook up all four, drop them together at the trailhead, bring them up together at the road, and they finish equalised rather than four slightly different numbers.

Why this matters: dropping tire pressure on the trail lengthens the contact patch, which gives you traction in sand, rock and mud that no amount of throttle will. The catch is the other half — you have to put the air back before you touch pavement. Low pressure at highway speed builds heat, and heat is what destroys tires and unseats beads.

For only a little more than the two-way, it halves the work again. If you air down on most trips, this is the one to buy.