When was the last time you checked the pressure in your tires? If you answered more than three days ago, you had better check them before your next ride.

Keeping your tires at their optimum pressure is one of the two easiest ways to keep your bike working at its best (the other one is keeping your drivetrain clean and lubricated). When your tires are under-inflated they wear faster, are much more prone to flatting, have increased probability of both rim and tire damage, and worst of all they have significantly more rolling resistance.

All tires have a maximum pressure printed or molded on the sidewall. In the case of narrow (25C or 1" or less) road tires, I feel the optimum pressure is 120psi or the maximum rated pressure, whichever is higher. Studies have shown no decrease in rolling resistance above 120psi, only a harsher ride. Mountain bike pressure is significanly less.

Tires with standard butyl (black rubber) tubes should have their pressure checked at least every three or four days (every time you ride them if you ride less than twice a week), and ultralight butyl and latex tubes at about half that interval. Keep in mind that if you use CO2 cylinders on the trail they seep MUCH faster and after you get home should be fully deflated and then re-inflated with good ol' air.

Speaking of fixing flats on the trail, here are some other tips. When fixing a flat, be sure to find the cause by feeling inside the casing for the entire circumference or it's likely to cause another one. I recommend always aligning the "hot patch" or tire label with the valve stem and on the drivetrain side of the bike. This gives you an easy reference point to find the cause when you get a flat by comparing the tire to the tube. Also inspect your tires frequently for glass or other debris and remove it before it has a chance to work its way to the tube and cause a flat.

You'll ride farther, faster, with less effort, and with less flats if you take the time to inspect your tires and check their pressure.

Larry Koh operates a mobile bike service in Southern California. The doctor is in at (805) 499-6427.