My new bike is a Giant LaFree (electric pedal assist) with 26 x 2.35 tires. The tires are CST Metropolitan Palmbay. I have had multiple flats on the front. The leak is always on the inside of the tube in the same place, where the ribs are. My bike shop sells me Sunlite 26 x 1.95 - 2.125 tubes. I have changed the inner rim strips to cloth ones, I run the tires at 60 psi (recommended on the sidewall is 22 - 60 psi). I'm not sure what to try next. Thanks very much, Robert
The Sunlight tubes I was using have a "ribbed" area near the valve stem. Patches just did not hold in that ribbed area. Inside the rim no sharp areas or spokes protruding, but I added an additional cloth rim strip and a Continental brand tube purchased from a different shop. It is holding for now, although this problem sometimes doesn't show up immediately. Here's hoping it is a good fix.
(later) I am happy to report that changing to a different brand of tube (continental) and adding a second rim strip has solved my problem of multiple flat tires.
we once had a batch of cheap tubes that all punctured near the same spot. i thought the odds of a defect like that were too long to take seriously but we couldn't think of any other reason. i know it's an unsatisfying and obvious answer, but i would try a different brand and see what happens.
if it still happens, well, i'm not sure. even the sticky-backed cloth tape can shift around on the rim after installation, exposing spoke holes that could puncture.
if your rim strip still looks like it's installed correctly, observe how narrow the center channel of the rim is. we used to have endless rim-side flats on cheap internet singlespeeds that came with rims that had an extremely narrow and deep channel. the tubes would get pinched there, but the puncture wouldn't resemble a typical pinch-flat with the two snakebite holes, it would looks just like a normal puncture. i contacter PureFix about it and they acknowledged the problem. if your rim has a very narrow and deep channel in the middle that could be causing it - try double and trippling up your rim strip (use the cheap rubber band ones over the top of the cloth).
For the puncture to appear in the same place, means that the cause of the puncture is not moving.
If the hole in the tube appears at a specific spoke hole, then check closely there for burrs. A sharp edge will "fret" its way into the tube.
If the hole is at one point on the rim, check the area for burrs.
If you rotate the tyre around the rim some amount, do the new holes move with the tyre or do they stay in the same place on the rim? If they move, that suggests the cause is embedded in your tyre and you need to look very closely. A wire or shard of glass is the likely cause, though I once found a thorn hiding.
Aside - learn to patch your tubes. A puncture should cost around 20c for a patch, not $5-$10 for a new tube every time. I've got one tube with a dozen patches, and as long as the new hole isn't on a patch or near the valve, its worth trying to save the tube.