Originally Posted by
DannoXYZ
No, they're toast, you need new tyres.
The rubber in the gumwalls holds the fabric strands of the casing in place and allows them to be positioned for load-carrying. Without the rubber in place, the casing will allow the tube to squeeze through between the fibres. You'll have a blow-out when you least expect it.
With respect to Danno, I disagree. Obviously neither of us atre actually seeing the ties, but I've seen many with dried flaking gum and the fabric intact and performing fine. Ad Danno points out the gum helps stabilize the plies a bit, but mostly it's just weatherseal. There's an adhesive between the two crossing plies keeping them form shifting, so you don't depend on the surface gum for that. I'd ride the tires but be attentive for any lumps or twists that might indicate the tire is failing. Also, if you see the plies separating anywhere where the tube could begin to balloon through, then the tire is surely toast.
BTW- I ride tubulars, and UV and rain destroy the thin gum coating very early on, yet I've gone thousands of miles on tires in that condition.