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I now have my first road bike. When I am pumping up the tyres with what seems like a sturdy pump (that you stand on and push with two hands), I can barely get to around 100 psi, even putting my back into it. Is this normal, or am I just weak?

Notes: Valves are obviously presta, which I 'unscrew' and depress to let a little air out before connecting the pump.

Cheers.

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See this answer: bicycles.stackexchange.com/a/10845/1584 –  Daniel R Hicks Aug 19 '12 at 18:35
    
What pressure are your tires rated? My road tires are rated at 100-120 and I have little problem getting 115 pounds in. –  Randy Minder Aug 19 '12 at 22:43
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Do you hear any air leaking out of the pump? Some pumps get a better seal than others. –  amcnabb Aug 20 '12 at 1:45
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I found this morning that the barrel on my track pump had become slightly unscrewed. This meant that I was using more strokes than usual to get to the desired pressure, and I couldn't quite get there. –  DanS Aug 21 '12 at 7:45
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I had missed an almost silly point: IF your pump has a piston area of 1 square inch, to press in 100 PSI, you'll need to press the handle down with almost 101 pounds. Most humans can not press down with more force than their weight (myself included), so, there is a chance you are not too "weak", you may be to "light" (i.e. not heavy enough). Shall this be the case, use a pump with a thinner cilinder (smaller piston area). With half square inch piston area, you'll need 51 pounds of force to pump up to 100 PSI. –  Jahaziel Aug 21 '12 at 15:34
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3 Answers

up vote 6 down vote accepted

I have had such experiences even at much lower pressures, (I ride diverse disciplines of mountain bike, so I use my tires around 40 PSI, but still...). I have found three main causes for inflation difficulty:

I will discard air leaks as this one is pretty obvoius.

1) Faulty valve: Some valves get somewow obstructed, and won't get air in as easily as it should. This has happen to me with three types of vaole: Schrader, Presta and Dunlop. To test for this, inflate the tube while it's off the tire. You should feel almost no resistance, since the tire is not there to build up pressure. The tube should inflate quickly. You can also try a different valve core (Dunlops are easily changeable, but not too widely used, Schraders require a special tool but are also easily changeable. Some presta valves are changeable but not all of them.

2) Pump design: Some pumps are simply, by design, not capable of much mechanic advantage, so it is harder for the operator to achieve high pressures. The force required to push down the pump's piston is the pressure in the chamber multiplied by the piston area, thus, a pump with a large area piston is harder to push, but, usually such pump will put in a bigger amount of air per stroke. As per my personal experience with a wide range of pumps, for a floor pump the best sacrifice is a pump with piston area of about one square inch (roughly one inch in diameter). It will be painfully slow for 2.5 downhill tires, but will easily pump the pressures required for road tires. (For my downhills I use a cheap pump that has a piston with 1.5 diameter, its quick, but you'd start to suffer at 45 or 50 psi).

3) (or 2.2 if wou will...) Flawed pump: This is somehow related to the previous point, but this reffers to some defect, design error, damage, wear, etc. I have used pumps that have restrictive hose, valve (almost any pump has a 'check' valve) or connector. If this is the case, sometimes these parts can be cnanged or modified, but most of the times, it's not worthy. To test for this, press the pump without anything attached. The pump should move freely, with almost zero effort and you should hear the air hissing out without restriction. In fact, you would not be able to exerpt any force donw the handle, it will quickly go down before you know it. If you can apply noticeable force, this may be the cause. This is more common with cheap pumps, but there are brands able to sell expensive ones from time to time. Restriction to air flow can also be due to debris that somehow got inside the air ducts or the valve. If the pump is serviceable with regular tools, then carefully disassemble it to check the hose, the connector and the valve or any other narrow air passages.

Naturally there are other issues tha can come up with a pump, but they are rather obvious and do not seem to be your case: such as piston seizure (It is difficult to displace the handle even as slow rate) or seal failure (gives the oposite symptom, you can not apply gerat force to the handle because the air is leaking out).

Perform some tests to discard possible causes: inflate someone else's tires with your pump, borrow a pump with different design as yours and use it on your tires. You'll easily find the culprit.

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When you have the problem that the tire is hard to pump from the start then a bad valve, improperly connected chuck, or something similar is a likely cause. But if the pump simply gets harder and harder to use as pressure goes up, then it is, as you suggest, the pump geometry that's causing the difficulty. –  Daniel R Hicks Aug 20 '12 at 21:38
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I'll add that the classic example of a pump with poor compression ratio is your inexpensive "compact" frame pump. Such pumps are rarely capable of achieving more than 50-75 PSI, even if you sit there and pump for 30 minutes. –  Daniel R Hicks Aug 20 '12 at 21:39
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My pump exhibits similar behaviour if I don't put the valve far enough into the pump head. I find that I have to put the pump quite far in, and that sometimes even though I hear air coming out before I lock the pump on, it's still not on far enough. Luckily I've found a way to tell if the head is on correctly before I start pumping. My pump has a "button" that you can press that will release the air from the tire (which is useful if you pump the tires up a bit too much). After attaching the pump head to the valve, I press this button for a few seconds. If the air flows freely out, I know that the valve is properly connected, and I will be easily able to pump up my tires.

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There is a problem somewhere. With a floor pump you should be able to get into the 110 range with little effort. Some pumps are not designed for higher pressures and this may be the cause, but I'm guessing something else is a bit askew here.

Without more information, my first thought would be to stop by your LBS. Any small shop and even most big ones will take the time to show you how to pump up the tire. Don't worry about this seeming "simple"...with all the different variants out there, even I have problems with some pumps and I work part time as a bike mechanic. If there is a problem with your pump (or possibly your valve, but if it's letting air out it's probably good), the shop will be able to diagnose and let you know what's going on.

If you want more: What brand/model pump are you using? What type of head does the pump have?

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A pump's max pressure is limited by its compression ration. A "general purpose" handpump (designed for car tires and kids' bike tires) will generally only be good up to 80-100, whereas a pump designed for high-pressure tires will be good to 140 or above. –  Daniel R Hicks Aug 20 '12 at 17:12
    
yep - hence my "what brand/model". –  Ken Hiatt Aug 20 '12 at 18:54
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But asking "what brand/model" is of little use unless the pump happens to be one of a small number of well-known brands/models where the design pressure can be identified. –  Daniel R Hicks Aug 20 '12 at 21:37
    
It's a Bontrager Charger with a smart valve and a pressure gauge which runs up to 160 psi. –  User 17670 Aug 22 '12 at 10:23
    
With that pump you should have no problem getting into the 110 range. If you are seating the head as Kibbee mentions and you are still having issues, then something's not working somewhere. Swing by your LBS with your pump. –  Ken Hiatt Aug 22 '12 at 13:40
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