SethL

Just purchased a bontrager floor pump with a psi monitor. Before this I just felt the tire to see if it was hard before going out and added air if it wasn't. As soon as I connect the nozzel to the presta valve the tire loses lots of pressure and after I finish it loses air when I detach. This makes it hard to know the actual psi of the tires. So if I am trying to get to 95 does it make sense to pump to 100 psi in and detach? Is this normal for a floor pump? I have 2 road bikes with 4 different tires and I have noticed this happening with all of them so its not the tires or the valves. .

aggiegrads

More than likely, the loss of air when you detach is air coming from the hose, not from the tube. If it leaks until you get the presta valve screwed down, then something is wrong with your valve.

79pmooney

There was a long thread on this maybe a year ago. Shouldn't be hard to find and every you could possibly need to know is in it. I'm a few hours out of surgery so I'm not going to look.

Eric F 

Don't worry about any loss while connecting the pump. As aggiegrads said, a little sound when detaching the nozzle from the valve is probably residual pressure in the hose and pump barrel. If you want 95, pump to 95, detach the nozzle, and go enjoy your ride.

In reality, pump gauges aren't especially accurate, so you're probably not going to be at exactly 95 anyway. If 95 on your pump gauge feels right, stick with it.

HTupolev

Most pump gauges are pretty inaccurate. Don't worry so much about what the exact number is, just figure out what firmness works for you and use the gauge to reproduce it.

2_i 

It should be possible to put on the pump's head on without disturbing the valve's pin. If you disturb it putting on, it is likely that you disturb it when taking off. Try to play around and see whether you can learn to move the head along the axis of the vent with no titling. After pumping there is still pressure in the hose, as was mentioned, but some pumps have a release valve for taking air out of the hose - do not know about the particular one.

Andrew R Stewart 

This is why some will use a separate air gage, just like a dishing tool instead of the truing stand. Andy

Sy Reene

Separate air gauges still need air to flow into them to give a reading, right? And then if you find out you need air, you need to disconnect (releasing air) the separate gauge anyway, and reconnect a pump (releasing air), pump, and then re-release the pump again (releasing air). oh.. the horror

Andrew R Stewart 

Of course they do. But the amount of air that fits inside the gage is far less then what bleeds out while fitting a pump chuck onto of off of the valve. Additionally it's far easier to determine the usual amount of pressure loss, from the tire, due to a gaging. Thus a correction factor is easier to figure out. Only those without a separate gage will use a pump as a gage. But if that's what you have...

To tangent and almost rant- It seems that air pressures are one of those go to specs that so many feel is a must have. I don't know how many times I see a bike in the shop with the max pressure , as the tire side wall states, in the tires. Just about every tire manufacturer considers the side wall listing as a max, not what any one rider should use. I have sometimes asked if the rider drives a manual transmission car with a tach in the dash display. When they say yes I ask if the shift the car's gears only when the RPM is at redline on the tach... In the real life (not the life that magazines write about) unless you are running tires that are on the extreme skinny end of the size range the need for exact pressures is pretty much not needed. After all if you're riding for a number of hours and the pressure drops that PSI or two during the day do you stop part way through your ride to top off? No, most just ride the bike.

Lastly it's well known for decades that you have better traction with less them max pressures and only fairly recently that you're faster with less pressure then max too. Andy

pdlamb

I'm going to come at this from a slightly different approach. If you're used to pumping a bike tire to "feel," do that with your new pump. Note what the gauge says. If the tire feels a little soft after you pop the chuck off, pump it up another 5-10 psi, note the reading, and check the feel when you take the pump off.

Now when you pump your tires the next time, pump it to whatever reading you were happy with the first time.

If ever there was a practical demonstration of Heisenberg's Uncertainty Principle, it's measuring air pressure in bicycle tires.

DaveSSS 

Google hirame pump head. They are pricey, but work wonderfully. You won't lose any tire pressure using one. Any chuck pushed on too far could hold the presta valve open and create leakage. The adjusting ring is set so the chuck slips on easily and the lever locks it in place. A properly functioning presta valve instantly seals when there is pressure equilibrium between the hose and tire. Pumps also have a check valve to stop back flow. If the check valve leaks, the pump handle will raise on its own.

I've posted recently on my calibration of my 30+ year old silica pump. It was reading about 8 psi higher than the actual pressure, so when I put 70psi in my front 28mm tubeless tire, it only had 62. Some pressure calculators actually recommend 62 front for a 135-140lb rider. I rode many times with this pressure.

Calibrating requires at least one gauge of known accuracy for comparison. I had three new liquid filled gauges that all agreed within 2 psi at 80.

Iride01 

I tend to think many air chucks let the user shove it way to far down on the presta stem. That was one of the issues with my old chuck that started requiring too much pull to remove it from the stem and causing several valve stems to start tearing out of the tube. And the now not so new replacement air chuck is starting to allow itself to be pushed to far on the stems. So probably time for me to get another air chuck for my pump.

All the chucks for presta I've used only need to be pushed down on the narrower part of the valve stem and then locked. Also, you need to know there is typically no pin in the chuck to depress the valve stem as there is in chucks for most schrader valves. So forcing the chuck on so far that you depress the valve is wrong. The valve will open as soon as you put more pressure from the pump side than is in the tube.

If you get an air pressure reading on the pump gauge when putting a presta chuck on the valve stem, then I'd say you need to consider if you are doing it wrong. You shouldn't see a pressure reading until you make that first pump to open the valve stem.

jadocs

This

Phil_gretz

^ this. Almost 100% of the bikes brought to me for service have overinflated tires. I'm guessing that many or most riders don't understand the relationship between the riding surface, the tire's volume of air, their riding weight and the proper tire pressure. I try to educate them... sigh.

MrWasabi

Great info in this thread. I think I've been a bit anal and overthinking my tire pressure.

cyccommute 

A Presta valve is a check valve and that is the beauty of that valve. When you pump air into it, the internal pressure pushes up on the valve and closes it. It has a “low cracking pressure” which means that it doesn’t need much pressure over the internal pressure of the tire to open or, more importantly, to close. Once closed, the pressure in the hose is meaningless. Don’t worry if any air is leaking out of the pump.

A Schrader valve, on the other hand, has to be held open. It’s a check valve as well but it has a very high cracking pressure. I’ve read that it takes 25psi over the internal pressure to crack a Schrader valve so it’s just easier to hold the valve open. That does mean, however, that if you hear air leaking, it’s coming out of the tire. It is possible to completely empty a Schrader valve tire while still attached to the pump.

cyccommute 

To tangent on your tangent: yes, but... The current fashion of dropping pressure to stupidly low levels is just as bad. People are running 40 psi in 35mm tires with a 200lb rider weight which is just asking for a pinch flat and/or damaged rims. Tubeless tire users constantly crow about how they don’t experience pinch flats but I’ve seen a number of ruined rims at my local co-op. The low pressure silliness is even worse for mountain bikes where people have told me that there’s no way I can ride off-road with more then 20 PSI in my tires. That’s just dumb...and certainly not within what most pressure calculators will give. My wheels wouldn’t last a full mountain bike ride at those pressures.

There’s another yabut in there, too. Decreased pressure results in higher rolling resistance...that’s where the traction comes from. There’s also a limit to how low you can go before the tires start to fold over and slow you down. I’ve ridden mountain bikes with 20PSI in them (slow leak) and the tire folds over in corners decreasing traction as the tire wallows around the corner in a very unpredictable manner.

I would also question that a lower pressure on a given tire makes for a faster ride. A wider tire makes for a slightly faster ride at a slightly lower pressure but rolling resistance decreases for a given tire as the pressure increases. I’ve never noticed that I’m faster as a tire is going flat...quite the opposite.

79pmooney

All "yes", except that with a careless tug of the pump off the valve, you can push the valve stem askew and crack it while pulling the pump off. This can happen if you don't pull the pump off cleanly in line with the valve stem. I was taught to remove frame pumps by doing my pumping at the 12 o'clock position for the valve, then knock the pump head off with a quick (and gentle!) karate chop straight down hitting the pump by the valve. I also am a huge fan of pump heads with lever locks like the Zephal HPs and HPXs have had for decades. My Specialized floor pump has one. Many others do too. (I don't understand why the all don't. Yes, there is the Silca tradition which has to be honored. But the rest? Zephal's patent had to have expired long ago.)

79pmooney

Careful! You're running counter to the modern "wisdom". All the previous gurus were just old farts without a clue. And remember, the current theory rules over experience any day.

(Says he who rides 23c @ ~107, 25c @ 102, 28C @ 94, 32C @ 88, all depending on the roads, weather and how he feels. I use the pump gauge at home but am just as happy using my frame pump and thumb. 155#)

Andrew R Stewart 

Good thread here! There's a lot of truth between the lines written. cyccommute's points are valid, as are mine. Real life falls between our comments. But (and you all knew there was a but coming) so many people either lack the ability to discover/discern for themselves or are willing to be led by others who are not the expert on the rider who is doing the inflating and riding. We seek affirmation and want to be thought of as "being right". What's the nut here is that there are many rights and wrongs when talking about shades of gray, like tire pressures. Andy (who it trading off below the waist work outs for upper body ones, as in snow shoveling)

I'll add that just because we can measure to the tenth of 1 PSI (or even a single whole PSI) does not mean it has meaning for your tires and riding.

djb

but also don't forget that some people are terrible putting on and taking off pump heads. I have a few friends who hate doing it and get very frustrated and flustered mostly because they fiddle faddle and have no timing and tend to let all the air out trying to put the pump head on--partly due to just be slow, and also for some reason not being able to line teh head up perpendicularly to the valve.

Koyote

This. Yes.

There was a thread a couple days ago - can't recall if you were in it. A poster was insisting that a rider must have a perfectly calibrated tire pressure gauge, and that the online psi calculators are sooo helpful, etc. He couldn't fathom that I (oh, heavens!) have figured out my psi on my own, and set it with with my one Meiser gauge - which I have not checked against any others.

I'm sure his head would've exploded if I mentioned that I will pump up my tires at the start of the week, and then ride for several days (with air leaking out!) before bothering to check again.

cjenrick

you could buy a good gauge and use it to calibrate your floor pump, mark a line on your floor gauge where, say, 100 psi is,

the human hand is a remarkable instrument, ever do autobody work? you know those tack cloths they use for removing fine particles of sanding dust before painting? well, a hand works better. use a tack clot and then rub your hand over the fender, you can feel every microscopic piece of dust on there, and the hand will pick it right up.

same with tire pressure. just feel the tires and not the pressure, after a while you will have calibrated hands.
this is handy when adjusting pressure for rain, or really cold days when the pressure will start to drop as soon as you leave the house. unless you pump tires in a freezing garage, which ani't a bad idea if you want the pressure to stay the same out on the road.

use to drop air pressure on the MTB at the top of a hill before descending and pump it up at the bottom, no gauge on the Silca so you used hand pressure.


when you flick your finger against the tire it will make a certain note, sewups made the loudest pop .you can use a Snark guitar tuner , i usually run an "F" in the front and a "F" sharp in the rear. (don't say G flat, bad karma)
unless you get a flat. then say, Gee, flat.

cjenrick

for the longest time, pumps did not have gauges, and the gas stations were no help either, no telling how many tubes i blew up with those gauges that had a plus/minus 100 psi tolerance,

got real tired of pumping up tires everyday, so we modified an emergency car compressor like you leave in the trunk, went to the hardware store and spent three hours trying to find the right fittings, but now it works on presta and schrader, robbed a couple of fittings, silca and maybe a golden rod, gauge shakes violently due to vibration so you have to be careful, built a 12 VDC supply with a heavy duty rectifier so we do not need a battery,

you know, i keep my bike in the bedroom, always working on it,
working on a bicycle is very relaxing in case you have not noticed.
there are times when it is not relaxing, that is when a tube lets loose at 3 in the morning,
so always wait til morning to inflate your tires if you bike is in your room.

djb

cjenrick, the reality of judging by finger squeeze is that the person has to be someone who is attentive and interested, and even with that, from my experience from 30+ years of touring, is that you have to do it regularly to develop the proper feel.
I've ridden long touring trips and get very good at judging pressures from both riding feedback and finger pressure, but that comes from day after day doing it.
I find that even at home, where I ride nearly every day on bikes with different tires and pressures, I can quickly lose and get wrong my guess on pressure.

so just saying, like the body repair guys, they do this each day, all day, and they develop it.
I reckon simply from riding so much, my finger pressure test is probably reasonably good even after months not doing it, but I'm sure I'm still wrong lots of times