Doh... a wee sidehop had my rear tyre come into contact with a sharp piece of metal about 4 miles into a planned 35 mile all day mountain epic.
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Normally damage like this would be game over but I carry a piece of old jeans/shorts material usually wrapped around my spare tubes and tool kit.
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It took a few goes to get it sitting right inside the tyre when the tube was blown up so as to not feel the constricted section of innertube - aim for the fabric tube to fit the tyre dimension not the tube!
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Continue on the ride the remaining 30+ miles including two fantastic fast rocky doonhalls with big rain ditches.
Throw tyre in bin when you get home 
or just cut a spare piece of milk carton/bottle and leve in your pack
A fag packet works too, with enough gaffa tape
Or a tyre boot. Many ways to do it; anything that salvages a ride is a good thing.
http://www.muddymoles.org.uk/tips/how-to-make-a-tyre-boot
I used a piece of bark on my road bike when the tyre blew out the side wall - got me home in the dark and rain 🙂
Also recently I purchased some nice thick fibre impregnated patches used for the inside of tractor tyres - they work a treat 🙂
Or you van do it properly with a weldtite external (or internal) tubeless repair kit for about £3.
An energy bar wrapper is the traditional tyre boot of choice. I once rode 30 miles round the New Forest flint trails using one on my Brompton with the kids. Only problem is that one has to eat the energy bar first 🙄
Or you van do it properly with a weldtite external (or internal) tubeless repair kit for about £3.
You can't do it with an external for sure as I already use one and you can't mend great big side wall rips like that!
An the internal patches are poss not strong enough for a side wall rip - not that I have ever repaired one like that - I'd bin it myself or use a bit tractor tyre patch and adhesive using a reinforced patch 🙂