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What's normal air loss for tires?

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What's normal air loss for tires?

Old 09-02-17, 09:28 AM
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What's normal air loss for tires?

After a series of flats averaging 10 miles/tube using a Performance Forte Metro tires I replaced both the tire and tube with a WTB slick and another Forte tube. There were some small bits of glass in the tread that couldn't be felt but were pressed into the tube during use, and both the rim and rim strip were new this spring. There's nothing on the rim that I can see that would cause a puncture either. The original tire has been used for years on both the front and rear wheels, and is inflated to a maximum pressure of 60 pounds. I usually check the pressure weekly, and often it seems like I ended up replacing the air lost by checking the pressure. The new tire can be inflated to 85 pounds, and I inflated it to 80 on Wednesday. The first ride I took was Friday morning, and when I got the office the pressure had dropped to 60 pounds. While that's a lot more pressure lost than the previous tires, it's not that different from the losses I'm used to seeing in my GF's tires that are inflated to the same pressure except for the time - she doesn't ride that often and it can be a couple weeks between rides for her and I've never checked the pressure in her tires after a couple of days. Searching the forums here naturally produced a variety of conflicting advice as to whether this is normal or not - am I going to have to top off this tire every couple of days?!?!
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Old 09-02-17, 09:32 AM
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80 down to 60 in a commute... you have a slow leak somewhere.
normally will go down a couple psi a day.
I check tires and top off before every ride.
A habit from riding tubulars for over 10 years.
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Old 09-02-17, 09:39 AM
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Losing 20 psi on one short ride is definitely not normal.
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Old 09-02-17, 10:51 AM
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To be clear, air loss has nothing to do with the tires. Any air loss is due either to permeability of the inner tube or a leak in the tube
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Old 09-02-17, 10:56 AM
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I'd say try it again - hope it was the valve not 100% sealed, and it seats better next time. From what you describe, I don't think you checked the pressure before your ride on Friday, so it was really two days and a ride.

I do find that when I put in a new (or patched) tube, I'll see more leak-down for the first week or two than later on. I run 700x28's at 70/75psi, and I only top up once or twice a week, once I'm past that initial period. I top up every day after replacing a tube.

I have a theory as to why, but really need to talk to someone better with fluid dynamics to see if it's remotely plausible.
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Old 09-02-17, 11:13 AM
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Originally Posted by Viich View Post
I'd say try it again - hope it was the valve not 100% sealed, and it seats better next time. From what you describe, I don't think you checked the pressure before your ride on Friday, so it was really two days and a ride.

I do find that when I put in a new (or patched) tube, I'll see more leak-down for the first week or two than later on. I run 700x28's at 70/75psi, and I only top up once or twice a week, once I'm past that initial period. I top up every day after replacing a tube.

I have a theory as to why, but really need to talk to someone better with fluid dynamics to see if it's remotely plausible.
Right, I didn't check the pressure before my ride on Friday, but I did check the valve when I got home and it was tight. The tube was brand new too, although I'm building up a collection of low mileage tubes with a patch. I'm going to check the pressure again before I go anywhere this weekend. I'm going to keep doing that to until either the problem resolves of gets worse. Thanks!
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Old 09-02-17, 11:32 AM
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There's no "normal" rate of air loss.

It depends on several factors.

Tire width - wider tires have a higher volume to surface area ratio, so they'll lose air slower
Tire pressure - pressure is the driving force, so the loss rate is roughly proportional to pressure.
Tube material - some materials are more permeable and allow air molecules through more easily.
Tube wall thickness - thicker walls resist bleed better than thinner ones.

While the first three are pretty much fixed by rider choices based on other things factors, the last is often forgotten about and can vary significantly. Different brands have different wall thickness, so a heavier tube of the same size may be preferable. Also consider that the tube stretches to fill the tire. A smaller tube will stretch more, thinning the walls in the process.

So, one way to slow bleed is to buy the largest, heaviest tube that fits rather than a smaller one used near the upper limit of it's range.
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Old 09-02-17, 12:17 PM
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I ride 25c tires at 100 psi. Usually commute 28 miles per day, MTThF. I fill up on Monday and again on Thursday. Tires are often down to 85-90 psi. I'll also fill up if I ride on the weekend. Weight with back pack and clothing is probably close to 170.

Generally, the higher the pressure, the rate of air leak is greater.

I agree that I think you have a slow leak. Odd that you are still seeing issues on both wheels with new tires and tubes, though. I can tell when I have an issue when I see either front/back having a much different pressure than the other.

Are you measuring tire pressure with the same device? You aren't losing a lot of air measuring pressure by misaligning the connector and losing air? I do that sometimes. Your situation seems somehow strange and I wonder what else is going on.
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Old 09-02-17, 05:03 PM
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Since it hasn't been asked...What are you filling your tires with? Ambient air? Nitrogen? Co2? or? Different gasses will cause different pressure drops.

I use nitrogen, 125psi drops to 100psi in a week, so I top it up once a week.

Matt

Last edited by awesomeame; 09-02-17 at 05:07 PM.
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Old 09-02-17, 05:11 PM
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Originally Posted by FBinNY View Post
Tube wall thickness - thicker walls resist bleed better than thinner ones.
I've never seen tube wall thickness listed on any tubes I've bought, but honestly I've also never been looking for it. Should it be listed on the box? Or is tube thickness generally thought of as thicker depending on the weight of the tube?

Matt
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Old 09-02-17, 05:40 PM
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Originally Posted by awesomeame View Post
I've never seen tube wall thickness listed on any tubes I've bought, but honestly I've also never been looking for it. Should it be listed on the box? Or is tube thickness generally thought of as thicker depending on the weight of the tube?

Matt
Sorry I confused you on this issue.

No, you'll never find wall thickness listed anywhere for two reasons.

The first is that the thickness will vary according to how the tube stretches when filled, and the second is that nobody cares.

But you can get a sense of the relative thickness by weighing the tube. The actual uninflated width also counts and this is probably more to the point. A wider tube stretches less in use, so ens up with thicker walls. So look for the widest size that will fit, ie. for a 38c tire, you want a tube marked fits 38-48mm rather than one marked fits 28-40mm.

Unfortunately, the markings on the box can be a bit deceiving. There's only a very loose connection between the marked "fits XXXX" and the actual width, so your best bit is to open the box and look at the actual width of the rolled tube. The actual uninflated width will be roughly 1.5 times the flat width, so working backward, you want a tube 2/3rds (tolled up flat) the tire's width so there's minimum stretch when installed and inflated.

Note, wider tubes can sometimes be a bit harder to mount without pinching, so if you run into mounting issues, buy something a bit smaller next time.
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Old 09-04-17, 01:29 PM
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Originally Posted by awesomeame View Post
Since it hasn't been asked...What are you filling your tires with? Ambient air? Nitrogen? Co2? or? Different gasses will cause different pressure drops.

I use nitrogen, 125psi drops to 100psi in a week, so I top it up once a week.

Matt
I'm filling the tire with ambient air. I checked this afternoon before the first ride since the post and had only lost about 5 pounds of air according to the same Topeak floor pump I last used to top it off. I'm going to keep checking for a while and hope thing settle down - it's been a while since I had to replace a tube and think I'm just forgetting how I had to do this before.
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Old 09-04-17, 01:36 PM
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I filled my tubes with Rogaine.

No more 'air loss.
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Old 09-04-17, 07:29 PM
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If nitrogen really did leak out more slowly than other gasses, the 70% nitrogen in atmospheric air would naturally distill as other gasses leaked out of the tube, eventually leaving you with all nitrogen. But it doesn't work that way, does it? Nitrogen inflation might make a small difference in aviation, where getting rid of all moisture matters, but not in bike tires.

I've found that tire thickness also has a bearing on air loss. While it's the tube that mostly holds the air, apparently the tire walls can also help to impede leakage.
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Old 09-05-17, 03:57 AM
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How about a soap test? Water + dishwashing liquid, swab it on the tire a small section at a time and look for bubbles. The air valve is a good place to start.
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Old 09-05-17, 04:16 AM
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Originally Posted by rgconner View Post
I filled my tubes with Rogaine.

No more 'air loss.
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Old 09-05-17, 06:47 AM
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All tubes lose air. Thats why I top off the pressure before every ride. The main reason is that you can track abnormal air loss which would indicate a puncture. Generally I ride every other day. The normal loss I see is maybe 5 pounds. If it is a lot more, I remove the tire and check the tube in water. If there is a leak, then of course I check the inside of the tire for what caused the leak.
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Old 09-05-17, 07:57 AM
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Thick heavy thorn resistant innertubes lose air slower than thin light tubes....
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Old 09-05-17, 08:49 AM
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Originally Posted by no motor? View Post
The tube was brand new too, although I'm building up a collection of low mileage tubes with a patch. I'm going to check the pressure again before I go anywhere this weekend. I'm going to keep doing that to until either the problem resolves of gets worse.

It might be worth you while to inflate the patched tubes (until they balloon up a little bit) and check for leaks in the kitchen sink full of water. If it bubbles, mark it and patch it.

Originally Posted by rgconner View Post
I filled my tubes with Rogaine.

No more 'air loss.

Boo, hiss.....
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Old 09-05-17, 09:41 AM
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Originally Posted by BlazingPedals View Post
...the 70% nitrogen in atmospheric air ...
Actually it's 78% (ie, close to 80%! reference: https://en.wikipedia.org/wiki/Atmosphere_of_Earth). The rest is correct! When the conversation turns to car tire inflation and nitrogen, I always mention that I fill my tires with 80% nitrogen; very few people are aware that it's just *air*.
Steve
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Old 09-05-17, 09:42 AM
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The thorn-resistant tubes I have bought listed their thicknesses. I've seen some tubes advertised as extra-light, which means thinner.

I didn't notice that the thorn-resistant retained pressure all that much better, but I didn't measure closely.
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Old 09-05-17, 09:43 AM
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Originally Posted by Arthur Peabody View Post
The thorn-resistant tubes I have bought listed their thicknesses.
Also, butyl rubber tubes are said to leak less than latex tubes.
Steve
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Old 09-05-17, 01:14 PM
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Originally Posted by BlazingPedals View Post
If nitrogen really did leak out more slowly than other gasses, the 70% nitrogen in atmospheric air would naturally distill as other gasses leaked out of the tube, eventually leaving you with all nitrogen. But it doesn't work that way, does it? Nitrogen inflation might make a small difference in aviation, where getting rid of all moisture matters, but not in bike tires.

I've found that tire thickness also has a bearing on air loss. While it's the tube that mostly holds the air, apparently the tire walls can also help to impede leakage.
Agreed. Such a hilarious scam. After the tire loses air a bit and you refill it, the very large majority (90-95%) of it is already nitrogen. Paying for nitrogen is... stupid.
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Old 09-05-17, 01:59 PM
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Originally Posted by sweeks View Post
Also, butyl rubber tubes are said to leak less than latex tubes.
Steve
The difference I saw was a lot. Latex tubes leaked down a lot faster than butyl rubber.
I don't recommend them unless you like refilling tires a lot.
With butyl tubes over a week I see a loss of about 15 lbs from 110 lbs on a 700x23c tire. I saw that much overnight on latex.
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Old 09-05-17, 02:16 PM
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Originally Posted by jack002 View Post
The difference I saw was a lot. Latex tubes leaked down a lot faster than butyl rubber.
I don't recommend them unless you like refilling tires a lot.
With butyl tubes over a week I see a loss of about 15 lbs from 110 lbs on a 700x23c tire. I saw that much overnight on latex.
Yes, when I've used latex in the past, I could count on 20 psi loss overnight. The payoff is several watts per wheel in power savings, more resistance to 'snakebites' and supposedly a more resilient ride.
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