So I bought a used road bike from WI recently. and just a couple days ago i got a flat. I took out the tube wanting to patch but saw that it was all patched up. So i decided to just buy a new on. the original tube was a "specialized 700x20/28c" but i bought a new tube according to the tire that stated "700x25c" and i installed it. It fit a bit big so I just shrugged it off and kept it. Within a couple of miles it popped tearing a big gash in the tube. I do tend to over inflate my tubes due to the roads near me. So my question is what tube should I get, what it states on the tire like "700x25c" etc. or what my original tube had? All help is much appreciated thank you in advance :-)

  • If you're consistently overinflating, you may want to switch to a bigger tire and run a normal pressure. Overinflating causes increased hazard damage, like underinflating does.
    – Batman
    Jun 30, 2015 at 10:39

3 Answers 3


If your tyre says 700x28c, that means your wheel has 700c of diameter and your tyre is size 28. You should buy a tube that perfectly fits this, and this is very easy as because tubes have, in the box, the diameter of the wheel they were made for, in your case 700c, and the range of the tires they are made for. So if the tube says 24-26 that is ok for you, if it says 24-28 that is also ok for you, etc. According to your description you bought the correct tube, so what the hell is wrong?

A few things might have made your flat, in particular there are three typical suspects:

a) Maybe your tyre has a glass or a small nail in it, and you didn't check. You removed the old tube and get the new one and the this fragment remained on the tyre, so it flat after a while.

b) Your rimstrip is weak and does not hold the pressure, forces the tube against the holes on the rim and they end up puncturing.

The solution for a) and b) is pretty simple. When you have a flat, remove the tube very careful so that you know it's original position on the tyre. Check if the position of the flat in the tyre and see if there anything stuck in it. If the hole on the tube is on the inside, then it's time to change your rimstrip to something more sturdier.

c) You did a bad job installing the tube. Make sure the tube sits perfectly inside the tyre, and that no parts remain stuck between the tyre and the rim before inflating. To do this it might help to inflate the tube a little but before installing, and check everything after installation but before inflating. Check this guide for detailed instructions.

As a side note, I personally don't like fixing tubes as the patch does not expand as well the the rubber of the tube when you inflate and you create a week point there prone to give some problem in the future.

  • it's can be a bad quality tube also, those in common strips on the joint.
    – Alexander
    Jun 30, 2015 at 11:58
  • I'm not sure what you mean by "those in common strips on the joint". I don't know what are strips and joint? OP says he bought a specialized tube so I assume problem is not from there.
    – super
    Jun 30, 2015 at 20:51
  • No. The original tube was specialized. But the new tube isn't clear what was it.
    – Alexander
    Jul 5, 2015 at 17:55

You mention "It fit a bit big so I just shrugged it off and kept it".

If the tube is the correct size for the tire, it should fit without needing to fold, shrug nor stretch. When you install the tube, it is advised to inflate it just enough for it to take shape, and no more.

If you put too much air in a tube that is outside a tire, there is nothing holding it, preventing it from growing. (The tube is just a doughnut shaped rubber or butyl or latex balloon).

When this happens the overall diameter of the tube gets bigger than the tire's diameter and this leads to a troubled installation. The correct thing to do is to desinflate the tube until it's diameter fits the tire.

A tube installed with folds or creases inside the tire won't be subjected to even pressure/tension along the material, so creating stress points that make it prone to failure.


If the tube was too big, it can have folds in it and that will make it pop too soon. I bought some Sunlite tubes a while ago. When I went to install them, they were too big in circumference. Both the tubes and the boxes were labelled the correct size but these were not 700x35 (27x1 3/8) They were more like 29" in diameter. I didn't install them. I bought other tubes. That was a manufacturer's error.

Don't overinflate. Buy tires with higher maximum PSI. I always inflate to 5-7 lbs. under maximum. If the temperature goes up, your tire pressure will increase. I've had more flats with tires inflated to max. so I no longer do that.

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