Login required to started new threads

Login required to post replies

Why does my latex tube... ?
Quote | Reply
(Didn't know how to fit the question in the title)

Why does my REAR latex tube lose air MUCH faster than my front?

Front wheel: Enve 5 (Smart, 650c); Rear wheel: Renn 555 650c (narrower than the front wheel)

I have changed tubes (I just use 700c latex tubes and kinda "insert" one part to another -- found that tip here in ST as well), and it consistently happens.

No problem with the race itself (I pumped in the morning (before 6 am), and it was okay for the whole 90km bike ride, which I probably ended 11 am). When I got the bike AFTER the race, they were still fine (using the pinch-o-meter). But the next morning, while the front was somewhat soft, the rear was nearly flat (maybe 10 psi), and two days after the race, the rear really is flat (but the front is still in the somewhat soft stage).
Quote Reply
Re: Why does my latex tube... ? [Alfalfameister] [ In reply to ]
Quote | Reply
This has just started to happen to me! Same thing 650c wheels. I have been using latex tubes for two years on both training and racing wheels. And recently that has been happening to my front wheel. I could pump it up and no sign of leaks, ride it for 60 miles, not notice any real pressure loss, then the next day it is flat. I have had the same tube in the front wheel for about year, and it was only recently that this would happen. I have taken it out and looked at it and have even moved the overlapped section and it does the same thing.
Quote Reply
Re: Why does my latex tube... ? [chaparral] [ In reply to ]
Quote | Reply
True. Sometimes even the front loses air FAST. Am glad it held up on race day.

My biggest fear is that I pump them both on race morning, but after getting back from the swim, to find them flat (or losing air fast using the said pinch-o-meter). And that fear will continue while riding the bike (which I was scared of; I kept looking down at both front and rear to see if they were getting softer).

But at other times, the front will hold "good air" for several days; other times, the next day it is flat as well. The rear, however, is almost always nearly flat 24 hours after.
Quote Reply
Re: Why does my latex tube... ? [Alfalfameister] [ In reply to ]
Quote | Reply
Removable valve cores? If so, make sure they're tight in the valve tube.

http://bikeblather.blogspot.com/
Quote Reply
Re: Why does my latex tube... ? [Tom A.] [ In reply to ]
Quote | Reply
Agree Tom.

OP; Also check the tiny o ring seals on the valve haven't perished or some crud has gotten in there...

Consider using some plumbers tape on the threaded male portion of the removable valve..

Also check the base of the neck of the tube where it attaches to the tube itself..
Quote Reply
Re: Why does my latex tube... ? [shadwell] [ In reply to ]
Quote | Reply
If it happens so fast that you are afraid of the race - then it is probably related to the valve.

There are always differences between latex tubes, some lose air faster than other, but should never be a problem during a race. (In a 15hour road race I inserted a bit extra at start, and finished at the lower end - within safe limits.)
Quote Reply
Re: Why does my latex tube... ? [Alfalfameister] [ In reply to ]
Quote | Reply
Alfalfameister wrote:
(Didn't know how to fit the question in the title)

Why does my REAR latex tube lose air MUCH faster than my front?

Front wheel: Enve 5 (Smart, 650c); Rear wheel: Renn 555 650c (narrower than the front wheel)

I have changed tubes (I just use 700c latex tubes and kinda "insert" one part to another -- found that tip here in ST as well), and it consistently happens.

No problem with the race itself (I pumped in the morning (before 6 am), and it was okay for the whole 90km bike ride, which I probably ended 11 am). When I got the bike AFTER the race, they were still fine (using the pinch-o-meter). But the next morning, while the front was somewhat soft, the rear was nearly flat (maybe 10 psi), and two days after the race, the rear really is flat (but the front is still in the somewhat soft stage).

I've noticed that the beige Vredestein latex tubes lose air at about twice the rate of the pink Challenge tubes....something on the order of 50psi loss over night versus 25psi. YMMV,

Hugh

Genetics load the gun, lifestyle pulls the trigger.
Quote Reply
Re: Why does my latex tube... ? [sciguy] [ In reply to ]
Quote | Reply
My tubes are the beige Vredestein.

I did check the removable valve cores, and they *seem* tight enough. Will disassemble and add teflon tape and reassemble.

Still, wonder why the rear loses air MUCH faster (could it be because they are 19mm rear rim (Renn 555 in 650c) width vs 23mm or so front rim (Smart Enve 5) width?).

I do pump the rear to about 110 psi, and the front to only about 90 psi.
Quote Reply
Re: Why does my latex tube... ? [Alfalfameister] [ In reply to ]
Quote | Reply
Alfalfameister wrote:
My tubes are the beige Vredestein.

I did check the removable valve cores, and they *seem* tight enough. Will disassemble and add teflon tape and reassemble.

Still, wonder why the rear loses air MUCH faster (could it be because they are 19mm rear rim (Renn 555 in 650c) width vs 23mm or so front rim (Smart Enve 5) width?).

I do pump the rear to about 110 psi, and the front to only about 90 psi.

While it's useful for sealing the type of extenders that screw on top of a valve down inside of a deep rim, I'm not a fan of using Teflon tape on the valve cores themselves as they already have an ""O" ring designed to seal properly. In my mind the Teflon tape has the potential to get caught in the valve and create a greater problem than it solves.

I would highly recommend checking the valve itself with a nice dollop of saliva placed all over the valve when the tube is inflated to full pressure. Saliva has just the proper viscosity and stickiness to stick around long enough to form a bubble even with a super slow leak. Water won't stick around long enough to do this. If there is a leak you'll actually see a bubble form and grow.

Hugh

Genetics load the gun, lifestyle pulls the trigger.
Quote Reply
Re: Why does my latex tube... ? [Alfalfameister] [ In reply to ]
Quote | Reply
So, we've documented a pretty large variance in bleed rates of latex tubes inside of tubular tires during my work with ProTour teams..on the order of 0.5-2.5+psi per hour at 100psi baseline.. the higher the pressure the higher the bleed rate.

Much of this is due to the way the latex tubes are made..they are all made by dipping a mandrel in liquid latex rather than extruding or molding, so there is always a variation in wall thickness around the tubes. Some brands are more consistent than others and some tubes within a brand will be more consistent, but even the really good ones have a lot of variance. If you put 20psi in one unconstrained, you will find really dramatic differences in wall thickness and the tube will have all of these areas where it is blown out into giant balls and other areas will be nice constrained little cylinders.

Secondly, you might have a very tiny hole or imperfection in the tube, the latex behaves differently than butyl and won't necessarily burst if you have a small flaw, so you could be leaking through either a pinhole or an inclusion in the latex that is allowing higher than normal transfer across the membrane..Also most all latex tubes have a valve stem bonded to a butyl flange that is then adhered to the latex, there could be a flaw or seepage at that interface which would be impossible to find once installed.

Valves are always suspect, the advice on removing and cleaning the valve core are good, you could also replace the core as I've seen those where you have a tiny crack or split in the plunger gasket and you will never get a good seal. I've found leaks in the valves, and the valve interface with the stem, sometimes it could be just dirt or some other debris or even some flash that wasn't properly removed during the rubber molding process that made it through into the finished valve core..

Lastly, latex tubes are sensitive to heat, you often see that the tube is rippled and discolored on the rim side after riding it for a few weeks or months. It is possible to heat flat a latex tube in one extreme heat event, but it is also possible to slowly damage them through repetitive heat cycling on the rim side, and this may be lead to accelerated bleed..

Not seeing it, it's impossible to say which of these things might be happening, but all are things I've seen before (more than once..) and there may even be other possibilities!!
Best of luck
Josh

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc
Quote Reply