porous inner tubes

[handlebar]

Pressure loss in my Radrunner tires disgusted me. I finally installed a different brand of inner tube. They hold pressure much better.

Ten days ago I set the pressure in my Radmission tires at 45. Today it was down to 40 and 35. Where do they get these porous tubes?

Butyl inner tubes appeared in WWII because rubber plantations were in Japanese hands. Butyl tubes became standard because they weren't porous like natural rubber tubes. I used to ride English bikes year round, with 1-3/8 x 26" tires at 60 psi. A bicycle had a pump to repair punctures. Otherwise, pressure never got low.

I want to replace my OEM tubes. Are there any these days that don't leak?

[JedidiahStolzfus]

I've been trying to figure out why I'm losing air in both my tubes on my RR2.  Seems the front is losing it faster than the rear.  After a couple of days, front will be down by 10lbs, the rear by 5lbs. 

[Eric7]

I use a bit of Slime, some people say Flat-Out is better.  I pump my tires once a year, twice a year, something like that.

[handlebar]

I've been trying to figure out why I'm losing air in both my tubes on my RR2.  Seems the front is losing it faster than the rear.  After a couple of days, front will be down by 10lbs, the rear by 5lbs.

To eliminate possibilities, I tightened my cores with a Slime Valve Core tool, which is a sort of torque wrench. Later, when I deflated one of the tubes to replace spokes, I found the core already loose. Now I knew why air loss had increased lately. That OEM tube had a valve whose core wouldn't stay tight.

[handlebar]

I use a bit of Slime, some people say Flat-Out is better.  I pump my tires once a year, twice a year, something like that.

Thanks for the tip. Years ago, I bought a can of tire inflator to use for slow leaks in the tubeless tires of a riding mower (probably at the beads). The sealer is latex, and the propellant is nonflammable and harmless to rubber. It didn't slow the losses in my Radrunner tubes. I'll try Slime or Flat-Out.

[tacomanatx]

I consider it a normal function of the tires to lose air.

When I used tubes in my MTB and Road (Tubeless now) they slowly lose pressure... refill every other ride or so.  On the MTB I rode slime and it didnt really make a difference.  Now that I am tubeless it still happens but a bit slower it seems.

On my Rad those tires are so big I dont have a feel for low so about once a month I pump them up.

[Eric7]

I think the theory behind the air loss are as follows:

1. Bicycle tire technology with inner tubes is old. You must not use today's car/motorcycle tires as a comparison. Tires lost pressure all the time in the old days.

2. All surfaces of the inner tube leak air at a certain rate.  Modern tubeless tires in a car are thick, with the road tread being part of the "tube." Inner tubes are thin, so the loss is greater.

3.  The surface-to-volume of a tire's inner tube is way higher than a car tire.  So any loss of air affects pressure greatly.  Whereas in a car tire, losing the same amount of air would not affect the pressure as much.  Similar to something like this:  A small cup of hot water would cool off much faster than a bathtub of hot water.

4. Modern tubeless tires were mounted with sealant of some sort to stop leaks at the bead and elsewhere.  Tubes (except for some) don't have sealants. Some modern cars don't even have spare tires because of sealant technology.

5.  Bicycle tubes are cheap. So not much care was put into making them.  They don't care about leaks when you can buy a tube for $4 and assume you will use some sealants, liners etc. if it is so important for you.

[handlebar]

I think the theory behind the air loss are as follows:

1. Bicycle tire technology with inner tubes is old. You must not use today's car/motorcycle tires as a comparison. Tires lost pressure all the time in the old days.

...

5.  Bicycle tubes are cheap. So not much care was put into making them.  They don't care about leaks when you can buy a tube for $4 and assume you will use some sealants, liners etc. if it is so important for you.

In 1972 I bought a BMW R75/5. The manual said to check tire pressure routinely. I could check without a gauge. In the first hundred feet, I'd zig and zag. If either tire was down by 2 psi, I could tell, and I'd turn around. While I was at it, i'd top the other one off. It may have happened at three-week intervals. Compared to my experience with butyl tubes, this was a nuisance. I'd owned two bicycles, which I'd ridden about 10,000 miles, and two motorcycles, which I'd ridden about 40,000 miles. They would stay at the proper pressure unless there was a leak.

BMW had switched to natural rubber because friction at high speeds was less likely to cause a blowout. Rubber latex contains chemicals that produce bubbles when the rubber is cooked in the mold, and bubbles made tubes porous. Butyl was cheaper and didn't contain substances that could bubble. By default, inner tubes are butyl.

Butyl tubes had taken over after WWII because they were cheaper to make and didn't lose air. If they are porous these days, I suspect that they aren't pure butyl. I think the formula was changed in response to pressure from manufacturers of ebikes and mountain bikes.

The manual for my Radrunner said I must run at the pressure on the tire sidewalls, no higher or lower, for safety. The tires were designed for Radpower, but the manual doesn't say what the pressure is. It was months before I found it on a sidewall. Why wouldn't the manual state the pressure it said was vital for safety?

In the 2020 Radrunner Electric Bike Review video, the founder of Radpower, who said he weighed 200 pounds, rode the editor, who said he weighed 130, as a passenger. The founder said he had 18 psi, 40% lower than the manual said was mandatory even without an overload. Radpower's business plan was to persuade consumers to ride at pressures that would cause a high rate of tube failure due to friction in the flexing of an underinflated tire. To compete for contracts, tube manufacturers must have added something to the butyl so that it would suffer less wear and tear from underinflation.

According to Amazon reviewers, some tubes that would fit my Radmission, hold air pretty well. Maybe there are still pure butyl tubes.

[Eric7]

Handlebar, Thanks for your insights.