Properly inflating tires

[spokewrench]

A compressor tank with less than 100% relative humidity would be unusual. Suppose ambient pressure is 15 psi. If I charge my compressor tank to 150 above the ambient, the absolute pressure is 10 + 1 atmospheres. The tank holds 11 time as much air as before it was pumped up. It won't hold 11 times as much water. At a given temperature, a space will hold only a certain pressure of water vapor.

At 25 C, the vapor pressure of water is about 0.5 PSI. That's how much water vapor a space can hold at 100% relative humidity. If the space is filled with air, approximately 1 molecule in 30 would be water vapor. If the shop is at 25 C and 50% humidity, the vapor pressure would be about 0.25 PSI and about 1 air molecule in 60 would be water. Compressing the air to 10 atmospheres above ambient, a total of 11, might increase the vapor pressure of the water content to 2.75 PSI. The tank could hold that at 60 C, but in my experience, the tank warms only slightly and soon cools.

If the tank sits at 25 C, its capacity will be 0.5 PSI of water vapor. The other 2.25 PSI, or 82% of what was pumped in, will condense and run to the bottom of the tank. If air from the tank expands to fill a tire at 45 PSI gauge, 60 PSI absolute, the vapor pressure in the tire will be .18, or 36% relative humidity.

If water can condense in air lines, it seems that in these cases, the pressure drop at the regulator is less than in my experience and the temperature drop is greater. I wish I understood the cause.

 

[PCeBiker]

OK, how about this,..
The pressure inside the tank brings the air inside to the dew point and fog starts forming.
That fog is in the entire airspace and is fed directly out into the air line.

You know they work.
You can see the water.

 

[spokewrench]

That makes sense. At night, when the air temperature falls below the dew point, the air may remain clear as water condenses on cold surfaces, but it can form fog. I guess the droplets could remain in the air if it was used at a high enough pressure and low enough temperature. It looks as if this filter works by having fog droplets stick to the screen (adhesion) and form larger drops that run to the bottom (cohesion).

 

[Catalyzt]

Yow. I hadn't thought about water vapor affecting tire pressure. Now I will.

The Marin 1 (with TSDZ motor) is running way better tubeless-- clearly less rolling resistance, and just feels less skittish even at higher pressures, though that makes no sense, gotta be my imagintion-- but I have two variables that are really impacting performance, and tire pressure is one of them.

The tires are Vee Rocco 2.3 29ers-- and the sealant is clearly still soaking in, they're still losing a lot of air (though I haven't measured how much). My fitness rides on weekdays are short-- 5 miles and 580 feet of vertical. (What I always say about living where we do is, you can't go 10 miles without 1,000 feet of vertical.)

I took the first ride on Monday night. Felt great! Bike had more grunt than the Motobecane with it's 40nm E5000. Felt like about 65nm of torque, just subjectively, though I know in some situations, the TSDZ can deliver a bit more. (And for some reason, the chainline is better after taking the cluster apart five times and putting it back together and remounting the wheel five times, which doesn't make any sense either, though that's another story.)

Took the second ride today, fighting the clock, trying to squeeze in a quick workout between clients. I know this ride usually takes about 26 minutes total with 20 minute of exertion (only six minutes when I'm not pedaling). But wow, the bike was slow today! I had a client at noon, and I was cutting it REALLY close-- yeah, I did it in just over 26 minutes as usual, but I was working a LOT harder. Pretty sure it is just the tires, (it is too soon in the charge for battery fade to be kicking in.)

The tires have a max pressure of 50 PSI, which is lower than I would like. My riding is really weird, mostly broken pavement, but I've got to have mtb tires because I generally ride about 20% dirt, and while it's not super difficult, some of it is right on the edge of a cliff, or with other obstacles. My solution to this is generally to fill the tires to 44 PSI, leaving some cushion before the max pressure. I bet when I check them tomorrow, they will be about 27 PSI, but they will start holding pressure better in a month or so. That's what happened with the Maxxis Ikon's on the Motobecane when I went tubeless.

A bad thing happened when I first filled the tires. The rear one was fine, the second one filled to pressure, too... our little terrier is sitting next to me on the floor, watching me intently as usual. Suddenly, the valve starts hissing. I remove the hammerhead from the presta adapter and start unscrewing the adapter. Then, the hissing gets REALLY LOUD.

The terrier and I exchange a split-second wide-eyed look ("Sh*t!") and then we both turn away and cower just as we hear a loud BANG. The valve core shot right out of the valve. Good instincts-- but I don't think that should have happened!

I'm glad neither of us got nailed.

 

[spokewrench]

Yow. I hadn't thought about water vapor affecting tire pressure. Now I will.

Uh-oh, I guess I'm the one who brought up water. I doubt a bike tire would get hotter than 50 C (122 F). At that point, water's vapor pressure less than 2 PSI, so who cares?

I have no experience with tubeless bicycle tires, but I have had leaks in tubeless car and mower tires. Sometimes it's around or in the valve, but usually it's a failure to seal against the rim. Seventeen PSI (44 down to 27) in your tire sounds like ~ 5 liters at ambient pressure. If I lost that much overnight, I'd seak the leak with soapy water.

 

[PCeBiker]

Thanks. That's the sort I've been looking at, maybe 2 years, and it has that kind of chuck I can get on and off with almost no air loss, and get it in with little clearance. I just found one of the same brand also with 6000 mah and a lever chuck, but it looks smaller and it's a lot cheaper. It weighs only 470 grams. Sold!

Keep in mind that you shouldn't leave the compressor in storage for too long without using/cycling it.
@m@Robertson mentioned that he left one in a duffel bag for a year and it died.

Charging it up to ~70% is good. Draining it then charging it back up is better.
They say every three months.
I just did that to mine two days ago.

You can use the built-in light if you have one or use the USB port instead of running the compressor.

Using it a lot eventually wears out the battery, but not using it can kill the battery.

 

[spokewrench]

Keep in mind that you shouldn't leave the compressor in storage for too long without using/cycling it.
@m@Robertson mentioned that he left one in a duffel bag for a year and it died.

Charging it up to ~70% is good. Draining it then charging it back up is better.
They say every three months.
I just did that to mine two days ago.

You can use the built-in light if you have one or use the USB port instead of running the compressor.

Using it a lot eventually wears out the battery, but not using it can kill the battery.

It was promising until I tried it. If the gauge had been inaccurate, I could have compensated, but this one is erratic, typically reading 2 PSI low before I pump and 3 PSI high when I finish. It's a shame. The one I bought a couple of years ago, which hooks to a car battery, has a precise and consistent digital gauge. Because the 16" hose is stiff, in use it starts unscrewing and leaking. The quick-release chuck holds very well, but on a light bicycle wheel, it's hard to pull it off without losing a lot of air.

Also in the photo is the manual pump I bought a month ago, shorter than most floor pumps so I could throw it in a box on a bike. I gave up on it because the chuck didn't work. Yesterday I discovered the secret. The quick-release chuck is open when the lever is down and locked when the lever is up, just the opposite of others. The cheap mechanical gauge is sure to be better than the digital gauge on the one I just bought.

 

[PCeBiker]

The cheap mechanical gauge is sure to be better than the digital gauge on the one I just bought.

The rechargeable compressor is still more useful and practical on the e-bike. You just need to check the pressure after inflating.
I've got a backup gauge in my tool kit as well, but I don't need to use it.

I've had lots of pumps without gauges, including an electric pump with a dial guage that was completely useless.

 

[PCeBiker]

,.. Yesterday I discovered the secret. The quick-release chuck is open when the lever is down and locked when the lever is up, just the opposite of others.

I've had both types and releasing by lifting the lever up works way better.
That's how my new compressor works.
The hose on mine is only 6 inches long and I don't want to dangle the pump by the hose when I connect the valve.
I hold the pump with one hand, and I can connect or disconnect the valve with one hand.

 

[spokewrench]

The rechargeable compressor is still more useful and practical on the e-bike. You just need to check the pressure after inflating.
I've got a backup gauge in my tool kit as well, but I don't need to use it.

I've had lots of pumps without gauges, including an electric pump with a dial guage that was completely useless.

The hassle of going back and forth between pump and gauge was the reason I was dissatisfied with my manual floor pump (still a great pump) years ago. (Similar pumps had dial gauges, but they went to 160 PSI or so. I figured they wouldn't be much good at 30.) I'd want to overinflate with the rechargeable pump, then use a gauge with a bleed button, like the inflator I use with my pancake compressor. To avoid rendering my reading wrong by losing air when I disconnected the chuck, I'd want a gauge with a ball chuck and clip, like the one I put on my inflator. I ended up using the inflator to get a good reading and bleed after using the rechargeable compressor. For the other two bikes, I turned on the pancake compressor. It was less hassle.

I'd love to get an adaptor to screw into the cordless compressor and connect to my inflator. Another option would be to use the rechargeable battery with my 12-v compressor.

 

[TrevorB]

Wow... $140 to $160 for the pump, and I'd need a $66 battery. Then I'd wonder when I'd need a new battery.

Most people buying these inflators already have batteries and chargers for other tools in range.

I bought a Ryobi one and it's been excellent investment. Quick to take 2.75x 2.3" bike tire from 0-50psi, don't know why but seem to be forever needing to do this and its not because of punctures.
Good for topping up car, RV, boat trailer, wheelbarrow tires. Quite often have to add few extra psi in car tires when towing, lot more convenient than going to local garage.
NB Ryobi wouldn't be my first choice if inflating large vehicle tires on regular basis, think Milwaukee had better reviews here.

If buying one of small portable bike tire inflators do your research as there are lot of lemons out. The more expensive ones tend to have better reviews.

 

[Jeremy McCreary]

Most people buying these inflators already have batteries and chargers for other tools in range.

I bought a Ryobi one and it's been excellent investment. Quick to take 2.75x 2.3" bike tire from 0-50psi, don't know why but seem to be forever needing to do this and its not because of punctures.
Good for topping up car, RV, boat trailer, wheelbarrow tires. Quite often have to add few extra psi in car tires when towing, lot more convenient than going to local garage.
NB Ryobi wouldn't be my first choice if inflating large vehicle tires on regular basis, think Milwaukee had better reviews here.

If buying one of small portable bike tire inflators do your research as there are lot of lemons out. The more expensive ones tend to have better reviews.

Totally agree. If you already have Ryobi batteries, the easy-to-use and inexpensive Ryobi inflator is hard to beat. Mine sits next to the bike's parking space in the garage. Since it's also a convenient digital pressure gauge, my tires get checked a lot more often now.

 

[spokewrench]

If buying one of small portable bike tire inflators do your research as there are lot of lemons out. The more expensive ones tend to have better reviews.

I've bought a lot of pumps over the years and remember only one lemon. That was a foot pump I once bought from Lowes on impulse when I ordered a shipment of building materials. It crumpled on my first stroke. I considered repairing it but then saw that everything about it was shoddy.

Other than that, my problem with pumps has not been whether they would continue to function but whether they were designed to fit my needs. I'd known that a foot pump would be slow and tiring compared to a floor pump. I'd bought it because it had a gauge. My old Bell floor pump could be considered superior to an electric pump, but the lack of a gauge meant I had to stand to pump, kneel to use a gauge, and stand again to pump. It seemed the only floor pumps with gauges measured to 160 pounds. Most households could use a tire pump, and few have tires that need more than 50 PSI. As you look at your feet, a 1-inch dial going to 160 won't show you 32 PSI as well as a 2-inch dial going to 60. Besides, a pump designed for 160 won't get a tire to 32 very efficiently.

I bought a 12-volt pump with an accurate digital gauge that showed precisely how much pressure was in the tire and shut off at the set pressure. It had a nice brass chuck that screwed down. They weren't cutting corners with that chuck, but choosing it was poor engineering. The air line exited not to the side but along the axis of the tire valve, which meant it required several inches of clearance above the valve. It wouldn't work on the rear wheel of my ebike or the front wheels of my mower. Air would escape as I unscrewed it, which meant I would no longer know what pressure was in the tire.

I replaced the chuck, but there was a basic problem with a tire pump powered by a car battery. It had enough wire to reach all the tires, and all that wire had to be unpacked and repacked with each use. Besides, it could not be used away from a vehicle with a battery. If I'd been smart, I would have checked the current draw at the highest pressure I expected to need. If I bought a suitable rechargeable battery, I would have had a portable pump with only a few inches of wire.

I bought a pancake compressor, but the instructions said leaving it charged would speed corrosion and the danger of explosion. If I had to wait a few minutes for the noisy motor to charge, I'd do all my tires at once, but that meant an involved process of moving things around to where they were in reach and I'd have room to kneel. It would have been smarter to buy a 5-gallon tank with a 3-foot air line and pump it up with an second-hand plug-in pump I'd bought years ago. They make aluminum air tanks. Maybe they can safely be left charged.

I should have bought a small 12 volt battery for my car-powered pump. Instead, I bought a pocket-sized pump powered by lithium ion. One reviewer said the gauge read 3 PSI high. I figured others would have reported it if they were all like that.

The pump seemed well made and the specs painstaking. The gauge, however, seemed erratic, typically reading 2 pounds low when I put it on a tire I'd measured with a trusted gage, and 3 pounds high when I took it off and then measured with another gauge. I decided to use it only to pump.

I ordered a digital gauge with a bleeder. It, too, read 2 pounds low. I found that if I took a series of readings, each was about 2 PSI lower than the last. Then I saw the problem. I couldn't avoid hissing when I pressed the chuck onto the valve and again when I removed it. In a bike tire, a little hissing can lose 2 PSI. In a drawer I had a ball chuck that I may have used 10,000 times from 1980 to 2020. I used it to replace the chuck that came on the gauge. There was no more hissing. In a series of readings, each would be 0.1 PSI lower than the last. (Without hissing, you still lose the air that rushes into the 16" of tubing between the valve and the gauge head.)

I realized that chuck hissing was also the problem with the pump gauge. It's the kind of chuck that clamps into the hose. I ordered a couple of a brand that I've used without hissing.

A good chuck probably doesn't cost more than a hissy one, and a hissy one can turn a pump or gauge into a lemon. A lot of pump manufacturers, gauge manufacturers, and even chuck manufacturers don't seem to know the difference.

 

[Catalyzt]

Uh-oh, I guess I'm the one who brought up water. I doubt a bike tire would get hotter than 50 C (122 F). At that point, water's vapor pressure less than 2 PSI, so who cares?

I have no experience with tubeless bicycle tires, but I have had leaks in tubeless car and mower tires. Sometimes it's around or in the valve, but usually it's a failure to seal against the rim. Seventeen PSI (44 down to 27) in your tire sounds like ~ 5 liters at ambient pressure. If I lost that much overnight, I'd seak the leak with soapy water.

Tires were actually 34 PSI when I filled them today, so they decreased by 10 PSI over the course of six days (and 10 miles of riding with 1,100 feet of vertical.)

If that continued, I'd be worried, but my money is still on the sealant soaking in. Also interesting that both tires lost almost exactly the same amount of pressure. I bet the loss will be down to 2 or 3 PSI per week in a month or two.

 

[Catalyzt]

I realized that chuck hissing was also the problem with the pump gauge. It's the kind of chuck that clamps into the hose. I ordered a couple of a brand that I've used without hissing.

A good chuck probably doesn't cost more than a hissy one, and a hissy one can turn a pump or gauge into a lemon. A lot of pump manufacturers, gauge manufacturers, and even chuck manufacturers don't seem to know the difference.

Another potential point of failure is the presta valve adaptor. They do not last forever, the seals do fail eventually, and very much as you describe: They may hiss, they may not, and for the non-hissing failures, it often seems like the pump has gone bad. Mine acted particularly strangely-- it shot way past the target pressure when it was supposed to stop, but it wasn't actually filling the tire to that pressure.

If you mean the type of chuck that clamps into the valve with a lever, I think that is called a hammerhead. (I just learned that yesterday.)

 

[fooferdoggie]

Tires were actually 34 PSI when I filled them today, so they decreased by 10 PSI over the course of six days (and 10 miles of riding with 1,100 feet of vertical.)

If that continued, I'd be worried, but my money is still on the sealant soaking in. Also interesting that both tires lost almost exactly the same amount of pressure. I bet the loss will be down to 2 or 3 PSI per week in a month or two.

it varies so much between tires. Plus sealant. I was using flat-out and I could go sometimes two months between adding air. but it always leaked out over time. my Schwalbe Marathon Almotion can go a month or more between needing air. but they sealed so well before I added sealant. most of the time its a couple of weeks. it can take a while on newly setup tires to really hold air.

 

[Rome]

Wow you guys are still on tires.
Mines are Eddy Current non rotatable. Front or rear application.
They are tubeless setup approximately 1500 miles on them and never had flat under inflated yes.

 

[spokewrench]

Tires were actually 34 PSI when I filled them today, so they decreased by 10 PSI over the course of six days (and 10 miles of riding with 1,100 feet of vertical.)

If that continued, I'd be worried, but my money is still on the sealant soaking in. Also interesting that both tires lost almost exactly the same amount of pressure. I bet the loss will be down to 2 or 3 PSI per week in a month or two.

Hmmm... air is 21% oxygen, and you've lost 22%. When linseed oil is used to make a nonstick surface on an iron skillet or a protective surface on a tool, it hardens by combining with oxygen. I wonder if sealant combines with oxygen. Maybe it ate up the oxygen in the air that was inflating your tire. If you lost your oxygen and topped off with air, you should have about 5% oxygen in the tire, meaning less absorption than before.

 

[spokewrench]

If you mean the type of chuck that clamps into the valve with a lever, I think that is called a hammerhead. (I just learned that yesterday.)

It does remind me of a claw hammer, but when I googled "hammerhead chuck" and checked Amazon, all I found was a chuck to secure drill bits.

If you want to avoid air loss when you connect or disconnect a chuck and a Schrader valve, the washer in the chuck should seal against the rim of the valve before the valve core is pushed open. A washer has to be soft to seal and then compress further for the chuck to push the valve open, and until 1927, soft washers wore out quickly. That's when Carl Norgren patented the ball chuck, using a soft washer that never seems to wear out. Almost a century later, most chucks are of designs that let more air escape.

 

[m@Robertson]

You said you and others in racing circles see a puddle after depressurizing a compressor tank by opening the bleed valve.

Yes. Its a teeny puddle on a 5 gallon tank. Half a teaspoon tops in my garage a mile or so from the seashore. More if the tank is bigger, I suppose. I only empty out my own tank and its a 5.

You said it's common to have to empty the water filter but didn't actually say you had to do it.

Well duh of course I had to do it

I guess if a lot of water accumulates in a tank and it gets sloshed, some could get into the air line.

No. The water is vapor. Naturally occurring. Ever-present. Its the reason water filters on air compressors exist.

In that case, traps must be doing their job. If there were condensate in a tire with 40 PSI at 47 F, it would help raise the pressure to 61 PSI at 180 F, not the 50 PSI you recall.

No you are mis-quoting me. Go back to Post 35 where I mentioned performance started decreasing right at around 50 psi. That has nothing to do with the potential for pressure increase you are talking about.

I hope the Hoosier Tire engineer didn't tell you to set the pressure lower on humid mornings because there was more water in the tire.

Initial cold pressure tends to be the same, but maybe gets bumped up or down depending on weather. The only mind you paid to humidity was when you put the water filter on your air compressor line.

I believe you reduced pressure to cling to the pavement better.

Reduced from say 52 to 46-48. What you were actually doing was reducing pressure so the edges of the tire tread stayed on the ground. Road racing slicks inflate like a balloon. Much more so than street legal tires. So as pressure increases you see wear completely stop on the outer and inner inch or so of the textured (slick) tread. That decreases surface contact, with the obvious effect, so you decrease pressure to lay the whole tread back on the ground. So yes you cling to the pavement better because you use all the rubber available again.