Any new noises, pulling to one side, braking changes, vibrations, electrical glitches, or water exposure since the last service.
Ride the bike in a sporty style. Listen for any abnormal noise or play. Go over a few bumps, roll down from a curb. Observe how the bike performs at full speed and during turns. Try reversing the bike.
Check for cracks, bent parts, loose hardware, missing fasteners, rubbing marks, and anything that looks “new” since last service. Make a few rotations around the bike so you don’t miss areas; gently shake panels and assemblies to find looseness. Keep an eye out for fresh paint cracks (can indicate stress, or even cracks in the main frame), exposed metal, misaligned panels, and elongated bolt holes.
Bolts fully seated, all nuts and washers present, no visible gaps; joints move smoothly but without looseness. From the front of the bike, grab both wheels and try to wiggle them in and out. Turn the handlebar all the way to one side, and move the wheel slightly with your hands, check for play in rod ends. Repeat for other side.
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Look over the wheel and the fender from the side of the bike, putting your head against the cargo box. See if the line of the wheel aligns with the cargo box. Grab the wheel with both hands and wiggle it back and forth to see if there’s any movement in the rod ends or ball joint.
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Test this by placing your hand on the end of the control arm and rocking it firmly in all directions. A breaker bar or a similar longer metal object can also be used. Feel for any looseness in the A-arm bolt or the ball joint. If you can feel movement in the ball joint when moving it up and down, it should be replaced. If you see movement in the A-arm bolt, tighten it. While riding, a worn ball joint will usually cause a sharp knock from the suspension when going over bumps. This is not a constant rattle, but a brief "clunk" as the suspension loads or unloads over a bump.
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For the bigger tires like Heidenau K66 or similar 80/80 ones, go for 1.4 bar or 21 psi. For the smaller ones like Vredestein cargo, go for 2.2 bar or 33 psi.
What to look for: cuts, bulges, embedded objects, sidewall cracking, and uneven tread wear. If a tire is leaking air, check the valve core and look for punctures. The most common leaks are on the side of the rim, or micro punctures on the tread. In this case tube/tire sealant liquid helps the most.