How often do you add air to your tires?

[dhgeyer]

As has been mentioned, always measure the tires cold, before riding, with a decent quality gauge.

Generally, tires will gain about a pound of pressure for every ten degrees (U.S.) increase in temp, and drop accordingly as the temp drops. Might this possibly be part of what you are noticing?

I check whenever there's a big temp change, in the morning, but if I know that the day will heat up I leave the pressure a couple of pounds low.

You can put in a lot more pressure than the GZ250 manual recommends. This will decrease traction a bit, affect handling to a minor degree, and dramatically increase tire life. You should never exceed the max pressure printed on the tire itself. The GZ manual recommends the lowest pressures I've ever seen in any manual - in the 20's. The max pressure allowed, as printed on my tires, is 36 pounds cold. I run 32 front, 34 rear. It's a trade off. Little bit harder ride, a bit less traction (not enough that I've ever noticed it), about another thousand or two miles before they need replacing. Maybe more, depending on how you ride.

Obviously I check my tires a lot. I have a bicycle pump that can make small adjustments quite quickly, much faster than firing up the compressor.

If your tires really are losing as much pressure as you say they are, something is not right. Unlikely that you picked up small nails or screws in both of them at the same time, so I would second alantf's idea, and get the little tool to make sure the valve cores are tight. I just had new tires put on my BMW, and the rear was losing about a pound a day. I noticed on my bill that they had replaced one of the valves, so the loose valve core was my first suspicion. I just tightened it up today, and it did seem a bit loose. I'll know tomorrow if that was the problem.

Hope this helps.