For all machine assembled bicycles and/or bicycle tubes with a Schrader valve, make sure you hand-tighten the valve core at the center of the valve using a “valve core” wrench available at any auto parts store. The machine-assembled valve cores are placed into the tubes and too loose. Everyone’s factory-tightened valves seem to leak up to 30 psi every two weeks. Hand-tighten the valve core and air will only leak through the tire, delaying the 30 psi drop until two months and 300 miles.
I hadn’t ridden a bicycle in 50 years, but know that exact tire pressure is always critical. I bought a brand new Giant Cypress and immediately upgraded the tires from the stock 700cc x 38mm to 700cc x 42mm. I was told my new bike would lose enough tire pressure every few weeks (from 85 psi to below 60 psi) to require checking and re-inflation. It did, losing 30 psi every ten days or so, on less than 40 miles of riding.
I found out how to maintain tire pressure two months longer on my bicycle: tighten the Schrader valves using a $2 “valve core wrench” available at any auto parts store. The valve core wrench is a small metal device only a few inches long. Air should not leak from the valve, only through the tire itself. The identical Schrader valves used on cars hold in air under much greater stress for months.
The Schrader valve has a cover that is removed in order to fill with air. The valve core is inside the round cylinder of the valve cover. The tiny stick in the middle of the valve is the center of the valve core. Tighten the valve core using the part of the wrench that looks like a narrow post with two long pieces coming straight out of its sides. Insert the wrench so the round post is on top of the tiny stick (long pieces going past the stick). Turn clockwise. Hand tighten the valve core with a few turns of the core. The entire valve coming up from the tube will be hard to hold as the core gets tight. During extended maintenance, it might be a good idea to loosen and then re-tighten the valve core instead of merely tightening it enough. The valve core itself can be removed and replaced anytime, particularly if it is dirty.
Both my Schrader valve cores were loose, apparently tightened only partially by the machine assembling the bicycle tubes to prevent damage to the valve’s connection to the tube. I guess this too-loose assembly of the valve core probably extends to all machine-assembled mass-produced bicycles. I don’t know if this applies to Presta or other valves.
Don’t go gorilla on the valve. Hand tighten as you would with other fasteners. You don’t have to use excessive strength and anyone who can ride a bicycle has more than enough hand-strength to easily make it tight enough. Apparently, we need to hand-tighten Schrader valves to get them tight enough to hold air normally because our hands are delicate enough to do the job without damaging the tube or valve. Be aware that your valves might have been hand-tightened during maintenance after it left the factory. Don’t tighten it so much you damage the valve’s rubber base connection to the tube.
After tightening my valves, it took three months and 200 miles to lose 30 psi! If you have any questions, get in touch with me through HBL.