rhlee

I bought two Schwalbe SV15's for my bike. I can pump them up, but overnight they will lose about a 1/3 of the pressure.

I pumped the tubes up to about 1.5 inches in diameter and immersed them in water, but I can't see any bubbles.

I would just get a new tube, but with both tubes having slow punctures, I'm not sure if I am doing something wrong.

It's been a while since I worked with 700c wheels, so I think I might have pinched the tube a few times with the tyre lever when I was putting them on. Could this cause small punctures?

Also I came a method for a method for finding small leaks (https://www.bentrideronline.com/messa...3&postcount=45) where you pour some isopropyl alcohol into the tube and look for any wet patches. However I'm not sure how I would get the alcohol completely out and am concerned that the alcohol left inside would damage the rubber. Has anyone tried this method?

Or should I just throw the towel in and buy 2 new tubes?

FBinNY 

I'll venture that any pinch leak you might have caused would have shown up in a bubble test. Also it's highly unlikely that you would have cause such matched leaks in two tubes. So you're likely looking at the normal bleed process, rather than a leak.

All tubes bleed air because of porosity in the material, the rate of bled depends on a variety of factors.

1- ratio of surface area to volume, with narrower tires therefore bleeding faster than fatter ones.
2- initial pressure with higher pressure tires bleeding faster because the air it trying harder to escape.
3- the porosity of the tube's wall. This varies with the material and thickness, with butyl (black) rubber holding air better than natural or latex rubber.

Narrow high performance tires and tubes do worse on all three scores, having high surface/volume ratios, high starting pressure, and thinner walls, or in some cases being latex vs. butyl.

You've heard of win/win situations? When it comes to holding air narrow HP tires and tubes are lose/lose & lose. 1/3rd of the pressure overnight seems to be at the high end of the range, but 1/4 overnight isn't rare at all.

If you stay with HP tires, buy a good floor pump, and be ready to top off daily.

digibud

If you are really losing 30% of your pressure overnight that is more than normal. Way more. If you have double checked that and it is true then some odd things might be in play. Maybe you didn't screw in the Presta valve entirely and there is dust in there causing a leak. Maybe you're inflating with C02 and it is diffusing through. Quite possibly the slow leak was so slow you looked at the water test too quickly. A very slow leak can be very slow even under water and they can be easy to miss. Personally I don't waste a ton of time searching for this kind of thing. Pinch flats are obvious and would show themselves in a water test. Blow the tires up even bigger, test under plenty of water, looking carefully at the inner and outer sides of the tire and then just put on a new one unless your don't value your time very highly.

10 Wheels

Do the water test again and check the valves under water. Move them around to see if bubbles show up.

FBinNY 

While there could be issues relating to valve problems or whatever, seeing it causing nearly identical leakage on two randomely selected tubes stretches credulity.

OTOH - the SV15 is a tube designed to be small enough to work with 18mm tires. If you have 18mm tires read point 1 of my earlier post. If you use it with a wider tire it's be stretched pretty thin on inflation. Read point 3 of t, thinner means faster bleed.

30% is a high bleed rate, but not outrageously so under the circumstances. I doubt you'll find a specific, fixable problem.

If you want tubes that hold air better, buy them so the lowest width of the fit range is closer to your tires. These will stretch less when inflated, leaving the walls thicker and reducing bleed.

rhlee

I think this is it. I have 25mm tyres. I'll try some tyres with a lower limit of/closer to 25mm.

Thanks again FBinNY.

hueyhoolihan

it would be normal for latex tubes to lose that much.

i know that latex tubes have been mentioned in this thread, but it got short shrift...

that would be the most likely case, although few people use them. OTOH they are sometimes bought and used by those that are unaware of their drawbacks.

you might want to give the tube a good squeeze on either side of the submerged portion to force evidence of a leak. or add more air. just a thought.

sunburst

good to know this. I've been buying smaller tubes to make tire installs easier. Always wondered if there was a price to pay.