This is something I've been fooling around with for the last few months and I thought someone might have some better ideas.
On long tours, tread on my 26 x 1.9s wear out in a few months. I want to extend that time by sticking something on the outside of a new tyre. If I could get a 1000km of wear out of the added tread at the start of a trip I'd be happy. Here's what I've tried:
Old tyre (with the bead cut off) stuck on with contact adhesive - pulls off within a few km.
Old tyre plus Liquid Nails - as above.
Old tyre plus silicon - as above.
Tube (slit about 2.5 cm wide) plus Liquid Nails - 20 kms
Tube plus contact adhesive - 10 kms
Tube plus Superglue - 400kms+
Tube plus Methyl Ethyl Ketone (PVC pipe adhesive) - doesn't stick at all.
Tube plus rubber cement (same as for patches) - no good (doesn't stick well to tyre)
Unless someone has other ideas, I've given up on using an old tyre. They're not flexible enough and soon pull off.
Using a tube and superglue is surprisingly effective. I thought the tube would wear out in a few kms because my experience when I've continued riding with a liner tube sticking through a worn-out tyre (I run a slit puncture-proof tube as a liner between the normal tube and tyre) is that you've only got a few kms left before the liner wears through.
But on the outside a tube seems to wear quite well. I got 400 kms - fully loaded around town - before I pulled the tube off to see how firmly it was attached. The superglue was cracked but still firmly stuck to both tyre and tube. I could see no noticeable wear in the tube and I reckon a tube may last a thousand km of more. The problem is, superglue is a pain to apply.
So, any ideas on how to add tread to a new tyre? The trick is getting something to stick butyl rubber and tyre compound.