Presta bicycle inner tubes can be tricky to fill if you’re used to Schrader valves. They are skinnier at 6mm vs 8mm and require an extra step before inflating. Further, they require a special Presta pump or an Autovalve pump.
- first you need to take the cap off of the presta stem (if it has one)
- next you unscrew the inner nut so the internal valve can release and accept air, test that it’s open by pushing in gently
- now attach your pump head to the stem and turn the lever to tighten down
- fill the tube to the recommended capacity which is listed on most tire sidewalls
Most mountain bike tires recommend 40 to 60psi while road bike tires are 100 to 125psi and you can vary this depending on your weight. If you are a lighter rider such as me, weighing 140lbs, then using 105psi for your road bike tire may be preferable because you will get more grip and traction. I run my front tire at 105 and my rear at 110psi since there is more weight on the rear wheel in most cases. Keep in mind however, that if you don’t have enough air in your tire you risk getting a pinch flat. A pinch flat happens when there is too much movement between the inner tube and the tire/rim of the bicycle thus “pinching” the tube.
Many Presta tubes come with a nut and cap but not all bike shops install these on new bikes. It may be laziness or to reduce the overall weight of your bike for maximum performance but they will usually give them to you if you ask. I recommend using the nut to stabilize the stem of the tube when inflating, this will hold the stem in place when attaching the head of the pump thus making it easier to get a tight seal. You could always keep one spare nut with you just for inflating and then take it off right after, some riders report that nuts can come unscrewed while riding and make noise but I have never encountered this.
If you are like me and have very nice rims made out of carbon, you might want to put a rubber washer between the rim and the stem nut to keep them from getting scratched. Deep dish rims also benefit from using a nut during tube inflation because there is more distance between the tire and the head of the stem, the nut will keep the stem from poking back through the rim or slopping around when pumping. Most deep dish rims require 60mm stems.