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Old 02-15-10, 09:33 PM   #1
Beerslinger
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Bike pump pressure question.

I was looking at pumps today at my LBS. I need a pump that will fill my tires to 110 psi. They had a pump that was rated to 80 psi max that the worker told me would be just fine to inflate up to 110.

How can a pump that's rated to 80 max psi inflate a tire up to 110? Wouldn't the back pressure blow the seals on the pump, or is there some kind of physics lesson I'm missing here?
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Old 02-15-10, 10:14 PM   #2
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I was looking at pumps today at my LBS. I need a pump that will fill my tires to 110 psi. They had a pump that was rated to 80 psi max that the worker told me would be just fine to inflate up to 110.

How can a pump that's rated to 80 max psi inflate a tire up to 110? Wouldn't the back pressure blow the seals on the pump, or is there some kind of physics lesson I'm missing here?
That pegs my BS-o-meter into the red zone. I doubt very much it will reliably go to 110psi and suspect he's just trying to make a sale and move on to the next customer with the least amount of effort. Generally speaking, manufacturers don't go to the expense of building a pump capable of delivering 110psi and then limit ttheir market and profit margin by selling it as 80psi max. that just doesn't make any business sense at all.

BTW, the best pump in the universe is the Topeak Road Morph.
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Old 02-15-10, 10:14 PM   #3
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The physics lesson is
Manufactures recomendation ≠ reality

Although this could quickly turn into a lesson of
Mechanics word ≠ reality
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Old 02-15-10, 10:19 PM   #4
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The physics lesson is
Manufactures recomendation ≠ reality

Although this could quickly turn into a lesson of
Mechanics word ≠ reality
If my 14mm bolt inexplicably became a 16mm bolt overnight I would be saying the same thing.
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Old 02-15-10, 11:07 PM   #5
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Just find one rated for 110, shouldn't be hard to do. If the bike shop in question doesn't handle road bikes much, that could be the problem.

Re: The Road Morph- that's not a floor pump, also not perfect- mine broke a while back.
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Old 02-15-10, 11:58 PM   #6
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Yeah, they normally handle MTB's. The 80 psi pumps had gauges, they had 1 110 pump but no gauge. I wound up getting a presta/schrader converter fitting so I can fill it up with my air compressor. It'll work for now, but eventually want to get a frame pump for when I start doing longer distance rides.
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Old 02-16-10, 02:09 AM   #7
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Cyclaholic must be psychic, then. Make it a road morph
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Old 02-16-10, 02:46 AM   #8
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A key difference between an 80 psi and a 160 psi pump is likely to be bore diameter.
A wider bore pump will push more air with each stroke, but quickly reach a point at which your physical strength can not match the force needed to push it. Wide bore is good for MTB.
Narrow bore pumps are good for high pressure, but take longer to get there.
For example:

The kitesurf pump moves a massive amount of air with its 15cm plunger, but only needs to go to 10psi or so.
The shock pump has a bore of around 1cm, and can go to 300psi. Good luck pumping a tire with either, you'd max out after 1/4 stroke, or spend all day.

Ask the mechanic to try the pumps out. Pump a tire to the pressure you want. That'll give you the best idea.
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Old 02-16-10, 04:51 PM   #9
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Just find one rated for 110, shouldn't be hard to do. If the bike shop in question doesn't handle road bikes much, that could be the problem.

Re: The Road Morph- that's not a floor pump, also not perfect- mine broke a while back.
Don't get one rated for 110psi- Get one rated a lot higher- It will be easier to pump the tyre to 110.

Take it this is a Frame pump so it will be carried on the bike. Only one pump I know that will get to 110 psi and that is Road Morph. Reliability is not a problem and it is probably the favourite pump for roadies. But Even with a Road Morph- I will struggle to get over 100psi. Smaller rider and just not enough weight or energy to get to that pressure. But If you can get the tyre to above 80psi then it will get you home- where you can use the track pump to get back up to pressure.

But if your frame can carry one- One of the old Frame pumps is the best bet. Problem is that you have to find a shop with a good supply of lengths to find one to fit your frame- and even then not all frames can take one.
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Old 02-16-10, 06:13 PM   #10
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The laws of physics can't be violated regardless of who makes the pump.

Pressure is rated in pounds per square inch. If you have a pump with a 1 square inch cross section, you'd have to push on the handle with 100 pounds of force to generate 100 psi. If the pump only had a 1/2 square inch cross section, you'd only have to push downward with 50 pounds of force to generate 100 psi but you'll have to take twice as many strokes to generate the same amount of volume for filling your tire.

Here's the bottom line. For road bike tires you want a skinny pump because otherwise you'll have to push too hard to reach the desired operating pressure. For mountain bike tires you want a fatter pump to generate more volume to fill a fat, lower pressure tire. Floor pumps, or pumps like the Road Morph, are good because they allow you to push downward with the weight of your torso.

The manufacturer's pressure rating is simply what they want you to think. Psi rating for a pump is meaningless without specifying the force required to reach it.
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Old 02-16-10, 07:55 PM   #11
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You can get a reliable floor pump that will generally be rated to something like 160psi. I'de recommend the Topeak Road Morph to carry. It's a very reliable unit and acts like a mini floor pump. You should be able to find options down in Courtney or Nanaimo.

Don't necessarily feel you have to pump your tires up to the maximum rating; instead go by your weight and road conditions. Here's a guide to tire care/repair
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Old 02-17-10, 12:00 AM   #12
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I'm a clyde at 275 lbs, so I figure I should have them near to max to prevent snakebits. Thanks for the physics lesson. I'll ask my lbs to order me in a roadmorph, and if they won't I can always go to the next nearest shop.
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Old 02-17-10, 06:45 AM   #13
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Some good info on tire pressures. I went from 110 to 85 and have not looked back.
http://www.adventurecycling.org/reso...SIRX_Heine.pdf
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Old 02-17-10, 10:29 AM   #14
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Topeak RoadMorph - end of story

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Old 02-17-10, 07:30 PM   #15
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Lezyne make on similar to the road morph but with more study construction, I didnt see one until I already had the Road Morph, with which I am happy/
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Old 02-17-10, 09:41 PM   #16
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Quote:
Originally Posted by cnnrmccloskey View Post
The physics lesson is
Manufactures recomendation reality

Although this could quickly turn into a lesson of
Mechanics word reality
What do those mean? I am not a master of hidden symbols of the keyboard. One must master the KIMCHI giggety giggety.
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Old 02-17-10, 10:04 PM   #17
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What do those mean? I am not a master of hidden symbols of the keyboard. One must master the KIMCHI giggety giggety.
That's the standard math symbol for "does not equal".
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Old 02-17-10, 10:14 PM   #18
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What do those mean? I am not a master of hidden symbols of the keyboard. One must master the KIMCHI giggety giggety.

Same as <> ? or >< ?
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Old 02-18-10, 10:09 AM   #19
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The Topeak road morph acts like a floor pump. There are several ways to pump. If you're a big frame person, you can get away with using your brute strength. If you're a 100 lb person, you need to use leverage. Using the torso to lean into the pump is not what I am referring to.

The pumping for a small person, has to come from the legs. To master this, you need to experiment with your floor pump first. Once you get the hang of it, then the Topeak road morph will be almost as easy. I say almost because the Topeak is smaller in size. But so is a 100 lb person.

I use the Topeak Joe Blow floor pump and at its base is the plate where you stand on to stabilize the pump while pumping. For me, I use the left heel and place it on the left side of the plate. My right foot is not on the right plate but rather about a foot behind. When I'm ready to push down on the pump handle, I bend my knees and keep my torso as straight as possible. That way my back does not take any of the pressure.

Usually around 90 psi, I will notice that the pumping gets more difficult so I will then use a snapping action when at top dead center. That is, when I'm ready to apply the downward pressure, it has to be one quick downstroke, with knees, legs, all insync.

The Topeak road morph is about the same way. But I have to say that a 6' 2" rider will have trouble trying to keep the back straight. The Topeak road morph is simply too small to do that for a taller rider.
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