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On my latest ride I managed to put a cut in the sidewall of my front tyre (Specialized S-Works Purgatory 26x2.2"). The sealant (Stan's No Tubes) didn't manage to seal the cut, presumably because the sealant lines the tread and not the sidewall.

While I was out on the trail I re-inflated the tyre and lay the bike on its side to seal the cut. Everything seemed fine until I got on the bike to ride it again, as the tyre rolled it deformed slightly and opened up the cut again. I managed to get home but had to re-inflate the tyre a couple of times to get there.

This post suggests the use of a Tire Boot but on the Park Tool site it suggests that it is only good for tubed tyres: "...in any tubed tire...".

As you can see, the cut seems fairly minor but the sidewall is quite thin, is there any chance of repair or is it time to invest in some new rubber?

Cut in sidewall

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    The Park Tool tire boot needs a tube to keep it in place, it does not have much adesive power on it's own.
    – Bibz
    Commented Oct 6, 2015 at 12:26
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    Pink bike did an article on this a few years ago. Their suggestion was a radial tire (i.e. car) patch on the inside provided the cut was a half inch or more above the bead (else, throw it out). Basically the same idea as patching a tube. Not sure what you can do on the trail for a cut tubeless tire though, other than put a tire boot and a tube.
    – Batman
    Commented Oct 6, 2015 at 12:39
  • @Batman I always carry a tube with me just in case I slash the tyre to hell out on the trail. I just re-inflated it to avoid getting the tube out. That article is excellent, the cut in mine doesn't look anywhere near as bad as the penknife one in their demo so I guess it should be fine. I'll keep you posted.
    – Phil
    Commented Oct 6, 2015 at 12:48
  • I'm always a bit skeptical of those things (note that the tire boot park tool sells is temporary, despite people using them for far beyond temporary). Normally, I'd just get a new tire, but that can get expensive. Completely YMMV, though.
    – Batman
    Commented Oct 6, 2015 at 14:40
  • As most are also suggesting the best trailside fix to get you home is a tyre boot and tube. At home a proper clean up of the area, removing all the sealant and an old school rubber puncture repair patch (vulcanizing fluid and all). Some people believe in super gluing the hole back together before patching, I've done both ways and not seen any difference.
    – DWGKNZ
    Commented Oct 6, 2015 at 17:46

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The solution to fix this was in the Pinkbike article suggested by @Batman in the comments to the question.

If you buy a radial tyre patch designed for a car then chances are it'll be plenty big enough to patch a hole in a bike tyre. I just went for some cheap ones on eBay. Add the vulcanising glue (plenty of it) to the inside of the tyre and stick the patch on. To be extra safe I added some glue around the edges of the patch after it was in place too.

As you can see in the photos below, there is almost no noticeable bulge on the tyre.

I've ridden the bike a couple of times since reinstalling the tyre and it has been flawless, no problems with the tyre and you certainly can't feel the patch when you're riding.

Radial tyre patch No visible bulge in the tyre

I realise there is no single solution that will work for everyone who finds themselves with a cut on the sidewall of their tubeless tyre but this solution worked very well for me.

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I don't know "the" answer, but a couple of ideas come to mind:

  1. Switch to using a tube in that tire, possibly with a liner.
  2. Use a tube patch on the inside of the tire and continue running tubeless. Having the patch on the inside means that air pressure in the tire helps to hold it in place.

Putting in a tube changes the role of the tire from air container to tube restrainer. That cut doesn't look too bad – but do look at the inside to see how much damage was done. If the threads of the casing are cut I think you may have trouble keeping the cut from growing.

I think the biggest problem you'll run into here is that the sidewalls are going to flex a lot and it may be necessary to have some kind of mechanical patch to prevent the cut from reopening if you continue running the tires without tubes.

If that is your front tire, I'd think about moving it to the back if you try patching it. The consequences of a blowout on the front are much worse that the rear.

BTW - clever move to put the bike on its side to get the sealant to work.

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  • I've never tried it, but using a tube patch for this will probably not work. A patch is designed to provide an airtight seal, not to contain the pressure - that's the tire's job.
    – Mike Baranczak
    Commented Oct 6, 2015 at 21:27
  • I would put the patch on the inside of the tire, not on the outside. Then I think the patch would be mostly in a role of sealing.
    – dlu
    Commented Oct 6, 2015 at 23:08
  • Putting the patch on the outside would be obviously nuts, but putting it on the inside would only be slightly better. I don't think the patch would be strong enough to keep this tear from getting pulled apart. It might work on a very small hole.
    – Mike Baranczak
    Commented Oct 7, 2015 at 4:11
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    What we need is experimental evidence. Does anybody have an old tubeless tire you'd be willing to sacrifice? Cut a 10 mm slit in the sidewall, put a tube patch on the inside, inflate and see what happens.
    – Mike Baranczak
    Commented Oct 7, 2015 at 4:15
  • I'm not keen on putting a tube in it as a permanent fix, I like the benefits that tubeless brings and I managed to get home fine without one but I think, like the comment by @Batman, I will give the patch a go. I'm going to try and source some patches that are more substantial than the usual puncture repair ones.
    – Phil
    Commented Oct 8, 2015 at 10:45

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