Patching Latex Tubes Near Valve Stem - Fixing Air Loss?

[ToffieBoi]

Hello everyone

Just after I ruined a latex tube while pumping, I looked closer to check the failure area.
Both sides of the valve on my both tubes were starting to have some defect. One just failed.
I am using Michelin 22/23mm latex tubes with 25mm Pro4 Service Course tires. 17C rims and 28mm measured tires. So tubes are stretching much inside.

Anyways, I threw away the punctured tube, and patched my new tube and the existing ones near the stem. Where they usually have problem. So they can't stick to rim tape, and this will fix the issue i believed.
I used Park Tool's pre-glued patch. Really thin, stretching well, light and sticking good.

So far, no problems, as you guess.
But I realised something new. Now, my tubes does not lose pressure that fast.

I had a ride on Sunday morning, and my tires were 80psi front and 90psi rear before ride. This morning (Tuesday), front is 60 and rear is 70psi.
Before patching, I was usually finding them around 40psi after 2 days.
Exact same setup, but patched tubes...

It seems that, at least for me, the main reason of the air leaking was from the valve stem, where 2 materials are joining. After I patched there, it is now really slow.

I wonder if anyone else here had similar experience?

[ToffieBoi]

I use the same tubes in 23mm wide carbon clinchers. Running Continental 4000s 23mm wide tires. I tend to loose about 20 to 30 psi per day as an average. The site you mention with these tubes tend to be the area of highest failure. I've been using them for about 5 years and the difference it makes in the ride makes it worth it.

It was my exact experience. But it is much more slower now, and only change was patching that areas.

By the way, is it safe to ride latex in carbon clinchers? I am about to buy 27mm wide chinese clinchers and wonder if you had any problems so far?

[WMW]

The site you mention with these tubes tend to be the area of highest failure.

Assuming you have the tube slightly inflated and installed properly, press or pull the stem against the rim tape before you inflate. If the stem gets stuck above the tape then you can get a lot of stretching before the air pressure is high enough to push it down.

[Valbrona]

If I have read this right ... Isn't it just the sharp edges of the valve hole in the rim damaging the tube? Sometimes a little bit of filing can sort it out.