Factual error: When Mouth flattens the tires on Brand's bike, all he does to let the air out is take the valve caps off. There's actually a valve in the valve stem that needs to be depressed to let the air out. The cap is just there to keep dirt out of the valve, simply taking it off wouldn't let the air out.
Factual error: The Goonies are from Astoria, but they ride their bikes to Cannon Beach; this is where the Lighthouse Lounge is, a distance of over 30 miles. When they descend in the tunnels below the lounge, they supposedly go under Astoria Country Club and Moss Garden. This would be impossible.