I have Mavix CXP-12 wheels (20mm). I have relatively new Freedom ThickSlick 23mm Tires on the wheels. I've been using these inner tubes: Meetlocks® 700x18-23c. I weigh 165 lb.

I just keep getting flats, both rear and front. More often the rear. Sometimes I get flats twice on a single 20 mile ride.

I was inflating to 110 PSI, and I assumed these were pinch flats, so I tried going up to 125 PSI and that just made things worse. Then I tried running at 90 PSI and that didn't help either. I thought the spokes seemed a bit loose and maybe they were poking the tube on bumps, so I tightened all the spokes a turn and that didn't help. I replaced the rim tape and that didn't help.

The tires are not compromised at all. The rims have no burrs or anything like that and the rim tape looks perfectly intact. These are definitely some sort of pinch flat. The punctures are usually on the side or inside of the inner tube.

I was having this same problem on another brand of inner tubes (I forget the brand name). So I doubt that's the issue.

I have no idea what's going on. Is there an incompatibility between these 23mm tires on my 20mm rim that leads to flats? Do I need to have the wheels rebuilt? They look perfectly true to me.

Any pointers appreciated. My only guess at the moment is I need to get 20mm tires. But I'm worried that'll just be a waste of money.

  • 2
    You might be pinching the tube when you are installing the tires. How are you putting the tires back on the rims after you replace the tubes? How do you ensure the tubes are not twisted or pinched by the tire? Are you using any tools to help force the tire over the rim? Commented Sep 6, 2015 at 1:09
  • I use a quikstik tire lever and another small plastic tire lever to help. I find it hard to believe I'm screwing up the installation literally every time. I don't know what you mean by "how are you ensuring." I inflate the tube a bit, work it into the tire, and then pop the tire bead back over the rim like everyone.
    – rjt_jr
    Commented Sep 6, 2015 at 1:26
  • 1
    Those tubes seem to have some questionable reviews. perhaps try a different brand of tube. Also, after installing, and before inflating, go around the rim pushing the bead away from the rim to check that there is no tube between the tire and the rim. after you've gone all the way around on both sides, you can be reasonably sure that it's not pinched between the rim and the tire.
    – Kibbee
    Commented Sep 6, 2015 at 2:13
  • 3
    What @kibbee says. Also try to see if you can get your tire back on the rim without using any tools. Sometimes it cannot be done for certain rim/tire combinations but often once you learn the technique you don't need tools for that activity. Commented Sep 6, 2015 at 3:24
  • 3
    Technique was the first thing to mind but the others have covered that. How about get some grease pencil and start marking where your punctures are - are they always on the same point on the tube? Same point on the rim? Or is the same point on the tyre always over the puncture? Though if you're trying other brands as suggested, this comment may be redundant.
    – Criggie
    Commented Sep 6, 2015 at 8:23

6 Answers 6


I've had this exact problem. I spent a whole lot of time removing the inner tube, patching it, etc... All to no avail. I finally figured out that the side of a drilled spoke access hole was barely visible next to the rim tape. When I'd inflate the inner tube, it would jut into that hole (depression) and get cut on the side of the drilled hole at the aluminum rim. The fix was to get better (wider) rim tape, and carefully adjust it so there was a uniform overlap at the spoke access holes.

I also figured out that is VERY difficult to patch a hole on the inner side of the tube. You have to use a patch that is at least two times its width (long axis oriented along the rim...)

Good luck with it.

Oh, and to help me in troubleshooting, I always label the fill port on the outside side of the tire (In my case I rotate the tire so the pressure rating is next to the fill valve. Then I use a paint pen to add a tick mark on the sidewall that exactly lines up with fill valve.) This makes the pressure numbers easy to find, AND really help me in troubleshooting a leaky inner tube. I can inflate the leaky tube in a bucket of water, find the leak, then remove it to line it up with both the rim AND the tire to search out root causes for the leak.

Edit.. I'm guessing that with certain rim cross sections and geometry, and with a soft rim tape, it might be possible for no sharp edges be exposed with tire and tube is off of the rim, but under high tire pressure, the rim tape may move a bit, exposing the inner tube to the sharp side of a drilled spoke access hole, or the end of a long spoke...

  • I didn't see any obvious gaps or other problems, but I replaced the rim tape on both wheels and now everything seems to be fine. There must have been something wrong with the rim tape.
    – rjt_jr
    Commented Sep 10, 2015 at 0:09

Slow down. You are a commonality here. Yes you may be installing improperly every time.

A smaller tire is NOT the direction to go. You want as big a tire as will go on the bike and run it at top of pressure range posted on the tire. Bigger tires have a bigger load capacity and are more pinch resistant. I don't like the super heavy duty tires as they have a hard ride. Get a heavy duty tube.

On my daily commuter I run 32 mm tires and only flat I got was because I was riding a tire worn way past the limit. It is a single speed and I don't even carry a repair kit.

On my workout/fun bike I run 35 mm and in 5 years one flat. The tube just flat out failed.

If you inflate the tube and then pop it on the rim you are not doing it like everyone else because I don't do it that way. Watch a video on YouTube. Inflate to give it some shape. Then deflate and get it on by hand. Get the tire down in the grove to get some room. I only have to use tools on brand new tight tire. Take it up to 10 psi and then deflate to let folds come out.

If that does not work then take the wheels into a bike shop an have them look at them. Don't just tighten the spokes a turn - that is NOT how to treat wheels.


Years ago I had a problem where I got flats every 20 miles or so. I fixed then many times with growing frustration until I realized that one of reinforcing wires in the tire had made it's way through the rubber and was poking out just a litte bit. Enough to cause a flat over time, but so little that I took me a long time to find it.

Just an idea in case the other (and more likely) suggestions don't solve your problem.

  • 1
    Just want to underscore the general point here – a puncturing object in the tire (like the wire in your case, or a thorn) that isn't removed will keep puncturing the tube until it either falls out or breaks off.
    – dlu
    Commented Sep 7, 2015 at 16:00

Note that proper detective work would identify the cause of this fairly easily.

Sometimes it's not possible when you get a flat in the rain at night on the side of the road, but in slightly more convenient conditions you should always take a few minutes for a proper post-mortem examination.

This starts before you even take the tire off. Ideally, use a grease pencil or piece of chalk or some such to mark the valve position on the outside of the tire, and also identify the left vs right side of the tire (and similarly keep track of left vs right side of the rim).

Remove the tube from the wheel (it's not always necessary to completely dismount the tire), mark the tube to identify left vs right side, just as you did with the tire, and inflate the tube to find the leak. When you find the leak, observe where it is!!

A hole on the inside diameter of the tube, where the tube is sitting adjacent to the spoke nipples, almost always results from a spoke poking through, or a defective rim strip which allows the sharp edges of the nipple to "worry" a hole into the tube.

A hole on the side, near where the edge of the rim would be, suggests a rough edge on the rim, a bit of wire poking out from the tire bead, or "snake bite" due to the tube getting squeezed between tire and rim when you hit a curb or other large obstruction. Note that "snake bite" will often, though not always, result in two cuts in the tube, maybe a half-inch apart (hence the name "snake bite").

A hole on the outer diameter of the tube, under the tread of the tire, suggests a "normal" puncture.

But having found the hole in the tube, you've only completed half of the investigation. Lay the wheel flat, lay the tire on (if it's been dismounted), and the tube on the tire. Use the marks you made earlier to position the tube and tire in their original orientations relative to each other and the wheel.

Observe again where the hole is (you marked it, right?) and check the same location on the tire and/or rim for any sort of foreign object or defect. This could be a bit of glass in the tire, a piece of wire, a large hole in the tire (needing a "boot"), a sharp edge on something, etc. Check both by sight and using your hand to feel -- sometimes you can see a defect you can't feel, and sometimes the defect can be felt but not easily seen.

Also feel around in the tire generally for a loose fragment of glass or some such. Sometimes a fragment gets in there and moves around.

About the only problem this procedure won't identify is damage from improper installation. Such damage is usually along the sides, and may have the appearance of a cut vs a pin-style puncture. But such damage usually is the result of using screwdrivers or metal "spoons" to service the tire, vs plastic "spoons" or a Quick Stick.


You don't mention where you're riding, or what "level" your tires are (the ThickSlick tires appear to come in a variety of builds with different amounts of puncture resistance), so it is a bit hard to comment on the problem.

If you're riding in urban areas where there is glass or other damaging materials on the road, it could be that the tires just aren't durable enough for the conditions where you're riding. They seem to be a relatively light tire, compared to, say, a Schwalbe Marathon.

Next time you get a flat take the time to really look it over, you need more evidence to figure out the pattern. As suggested, mark the puncture and work methodically – you want to remember what you did so that you can see the patterns. Here are some specific things to look for:

  • I don't think you're getting pinch flats, but they are pretty easy to recognize – pinch flats result in two holes, like a snake bite, where the tube gets caught between the rim and the tire as you hit an obstacle. Pinch flats mean you need more pressure. If you can't increase the pressure, then a bigger tire is in order.
  • Punctures from objects working through the tread cause a puncture that is usually on the outside of the tube (opposite the side with the valve) and often you can find matching damage on the tire – even if the object is no longer embedded in the tire.
  • A flat due to spoke damage would have the hole on the same side as the valve.
  • Your description of mounting the tire and tube sounds reasonable and it does seem unlikely that you'd do it wrong every time, but do practice to see if you can do it without tools, that will lessen even more the chance of damaging the tube as you mount the tire. Many procedures for changing a tire suggest working around from the rim splice to the valve hole. On most tires, you won't need tools at all, but if you do it will be for the last couple of inches. If you work towards the valve that is where you'd pinch with tools, so a puncture there might indicate damage from a tire iron.

The other posts offer a useful bunch of suggestions and might as well have solved the problem, however let me point out at the tyre size aspect. How did you measure your rim? Are you talking about the inner rim width?

Have a look at this page for compatibility matters: http://www.betterbybicycle.com/2014/04/a-simple-guide-on-essentials-of-wheels.html or at the Sheldon Brown page: http://www.sheldonbrown.com/tire-sizing.html

If you measure correctly and see that your tyre size is adequate for the wheel, then, check your tyre and rim carefully.

As your punctures are in the inside or sides of the tube they are not caused by external agents such as nails, pins, glass, etc., but by some barb in the rim or anything in the tyre sticking out into the tube or even a deficient rim tape as mentioned in zipzit post.

If the tyre size is not right, especially if it is undersized, the ill fitting might be causing the inner tube to squeeze itself between rim and tyre.

Let us know what you have found.

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