How do you fill a presta valve?

Discussion in 'Beginners Forum' started by Mike1jw, Sep 21, 2009.

  1. Mike1jw

    Mike1jw Member

    I have seen a lot of youtube clips on how to fill a presta valve, but none seem to address this issue. First of all, is there a way to check the pressure on a presta valve with an air pressure gauge? I bought a floor pump with a gauge on it but I'm still wondering how you know if you have the right pressure. When I inflated the tires on my old bike (car valves) I would usually over inflate a little and then as I checked the pressure with the air gauge the tire would lose a few pound each time I check it until I got it down to the right pressure (65 lbs) If I check it one more time it would be under inflated and I would have to start all over. So I’m wondering, if I attach the air pump and inflate to 120 lbs, doesn’t the tire loose some pressure when I remove the air pump? Should I over inflate a little to compensate for this? How do I know if my tires are at the right pressure?
  2. hophead

    hophead New Member Tavern Member

    If your floor pump has a gauge, you're good to go. Yeah, you are going to loose a tiny bit of air when you remove the pump from the valve, but not enough to make a difference.

    The floor pump gauges are not quite as accurate as a hand held gauge. If you really want to get your pressure precise, get a hand held. I have one, but rarely use it. I think it's made by Topeak.

  3. Mike1jw

    Mike1jw Member


    What I notice about bicycle tires is, that (I guess) since the air VOLUME is very small, the slightest release of air, drops the PRESSURE quite a bit. That being the case, and especially with narrow road tires, where there's even less air volume, I thought that it might be necessary to over inflate a little so the pressure drops down to where you want it when you disconnect the pump.

    Also, I have a button on my new floor pump to release the pressure before I disconnect the pump. I guess I'll get used to it.

    I know I must sound like some kind of nut asking this question, but I want to go for a ride this afternoon and it will be the first time I fill these tires. I hear that it's important to keep your tires at the maximum pressure, and I didn't want to screw up the first time I did this. Thanks
  4. mtndoc

    mtndoc New Member

    I'm thinking maybe a few trial inflations with the gauge on the pump checked with the hand held gauge to see what the actual pressure is when you remove the pump would give you a pretty good idea of how much air is actually in the tire after you remove it. Just a thought, but then you would know.

  5. wild

    wild Yesterday tired old man, Today retired old man

    If you do over inflate the tire a little so as to have the presure you want when disconected, I would not go more than 4 or 5 pounds over max. I had tires on the old bike that I kept 5# over max one day I went 8#over max and I ended up with a buldg in one tire.
  6. fatandslow

    fatandslow New Member

    That sounds like a problem with the tire. My experience has been that the max pressure for road tires is pretty conservative. I've inflated my 100 lb. max 700x28 Armadillos to 120 numerous times with nary a problem. Of course these tires are very heavy (duty). I always err (just) on the side of over-inflation to prevent pinch-flats. Probably marginally harder on wheels, though I try to ride "light."
  7. jusdooit

    jusdooit New Member

    You don't really need max pressure ALL the time. Slightly lower pressure will give you a little better grip in sharp turns. You'll also want lower pressure on wet pavement to give you better traction. While it's true you don't want pinch flats, a slightly lower pressure will give a smoother ride. The gauge on the pump should be about right.

    Over inflation can cause the tube to bulge around the rim if the tire is not properly seated causing a blowout.

    Really don't worry too much about this. Just ride and have fun! :D