I had a blowout the other day. On investigation, it was a C-shaped cut in the tube. It patched okay and on reinstalling I found this culprit :

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The tyre is not new but its not old either - plenty of tread left.

I've seen very old / weathered tyres where the rubber has deteriorated and the bead has separated but the cords remain. However this has torn about 20mm worth of cords.

I've wondered if it was too-high pressure, but the tyre sidewall says 40-65 PSI and I run them at 50-60.

The tyre may be too wide for the rim - but its the original tyre which came on this bike from new.

There is no noticeable roughness on the rim at any point, so abrasion seems unlikely.

The bike is a 20" folder and has done 1,300 km since I bought it used. Previous owner did minimal riding, so its done maybe 1,500 km total (1000 miles)

Lastly, I do occasionally use this bike as a tractor to tow a trailer. Its done 50km towing some amount of weight on a rear-axle mounted trailer, and despite moving some decent loads the nose-weight of the trailer has never been more than 10-12 kg (20-25 libs)

Question What was the cause of this tear in my tyre?


  • Yes this is the rear tyre.
  • Its a folding bike that started as 1x6 and this wheel was rebuilt onto an 8 speed cassette hub so its 3x8 gearing.
  • yes it has rim V brakes
  • 1
    Was it your rear tire? When towing, your rear wheel gets a lot of lateral loads and other things it's not really designed for...
    – RoboKaren
    Jul 12, 2017 at 22:59
  • 2
    Looks like possible brake pad rub, like maybe one side got bumped and off kilter and was slowly rubbing and weakening a section of tire that was not perfectly seated. Or that portion of the tire bead was defective and slowly being pushed out by the tube to where the pad could then make contact. The way it is frayed on the bottom looks like something was rubbing it.
    – Nate W
    Jul 12, 2017 at 23:24
  • 1
    The brakes seem to be leaving tracks on the rim a good 1mm or more from the tires. And the area fore and aft of the hernia don't show any brake rub.
    – RoboKaren
    Jul 13, 2017 at 1:28
  • 1
    Two thoughts - bead damaged from (previous) tire removal - happens if things like screw drivers with sharp edges are used in place of tire levers. . (I'll blame the previous owner :0 ). Bead could also damaged from hitting a curb / rock hard with low tire pressures, although these usually dent the rim.
    – mattnz
    Jul 13, 2017 at 1:35
  • 1
    While I doubt an experienced mechanic would damage a tire putting it back on from misusing levers, I have had experiences where a very old tire would fail this way just from the rubber being too dry and old. Was the tire put back on with levers? It looks like a big enough tire to be reseated by hand but it's a very possible cause.
    – Gabriel
    Sep 7, 2018 at 20:12

5 Answers 5


I've had a few tyres (well... 3) split like this. I'm pretty sure it wasn't the brake block rubbing.

In one specific case I went through a pothole and heard a clunk as the tyre flattened out completely. A few days later my tyre split like this and there was a visible mark on the rim at the same point that would have been from the pothole. I think the other 2 cases were less dramatic versions of the same thing - the tyre flattened out due to a pothole, bump or stone that caused a small tear that gets flexed back and forth until it finally gives way.


You mentioned that it's your rear wheel and that you tow a heavy load. Rear wheels in these setups get a lot of lateral (sideways) loading from the trailer.

This can put stress on the bead that it's not designed for. A higher pressure would help stop the tire from rolling side to side -- but you've said you're already on the high end of its pressure range. Maybe look for a tire that is known to have stiff or reinforced sidewalls.

I'm going to call herniated sidewalls: a "criggie" from now on.


I've lost a (front) tyre to similar damage caused by a sticking pressure gauge. At a rough estimate I put 120psi into a tyre rated for 85 after dealing with a normal puncture (broken glass in the tread). That pump stays on my frame in all weathers but it's not the one I use for topping up or planned changes.

About a mile after getting going, a fairly sharp turn and some bumps left me thinking "that sounds like the brake's driving on the sidewall, I'll stop under the next light... that feels like the brake's rubbing on the sidewall... bang". There was probably a slight weak spot but the tyre hadn't worked very hard.

So on top of any other causes I suggest you check your pump gauge. Pumping up with very cold air then leaving in the sun can cause quite a large pressure change, but I doubt that's the issue in this case.

  • 1
    Fair thoughts - it was not freshly pumped up, and I'd literally ridden 150 cm when it popped. So the damage had already been done.
    – Criggie
    Jul 13, 2017 at 7:36

I just had this happen to my rear tire. I was confused at first because the tire didn't make it to even half its normal life span before failing.

It turns out I had ridden the bike a short ways during a previous flat tire event a year ago and the wheel rim edges in the bead area had gotten a rough finish on them from making light contact with the asphalt. These rough areas acted on the new tire's surface area at the point of rim contact like sandpaper (or a nail file) little by little until strands of the tire were cut away, weakening the casing and causing the tire to fail.

I cleaned up the wheel rim edges to be smooth again and am back in business (with a new tire).

  • Welcome to SE - and thank you for your contribution.
    – Criggie
    Sep 6, 2018 at 10:42

There are three variants how this type of tire failure may happen, two of which have already been described in other answers:

  1. Local damage to the tire due to bottoming out on a pothole (see WyD1234's answer)

  2. Overinflation due to wrong/faulty pump (see Chris H's answer)

  3. Global damage to the tire due to underinflated riding.

    If you ride a tire with a pressure so low that it (almost) bottoms out during normal riding, this will damage your tire. With the result that the tire may blow out in the way you've shown any time later. This type of damage acts like a time-bomb: The actual blow out may happen when you are not even near your bike. And you won't know something's wrong until you have the exploded tire.

    It is enough to just push a bike for some distance when one of its tires are flat due to a puncture (I did that once). Even on a brand new tire (my experience again). So, whatever you do, make sure that you don't ride flat tires.

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