I "was" in love with my Grifo's until this year's pair. They keep peeling off the rim whenever I run lower than 32psi. The bead lifts out enough for the tube to stick out. Awesome tire, but those guys need to tighten up the bead a little. I should have expected problems when I put these on, and they went onto a standard Mavic Open Pro rim by hand. I stopped using them this season.
I actaually had that happen quite badly to a pair of grifo's I had. The front I was able to fix simply with some clear superglue, but the rear proceeded to get worse (considering the lower rolling pressure and strain. I contacted challenge and sent some pictures and they quickly sent out some new ones. I only had one small spot on the new ones where they started doing that again. BUT since i went ahead and aqua sealed those, it seems to be holding it down better. Since they are hand made, it's rather unavoidable. I know. Bummer. I guess thats the downside to some lonely man sitting in a warehouse strapping rubber to cotton.
Give them a call. Hopefully they will be as helpful for you as they were for me.
I have it currently happening on two sets of Grifos. One is a clincher version (both front and rear peeling in half a dozen spots or more). The other is tubular and only a couple small spots where the tread is loose on the edges.
Never happened on my Dugasts, even after serious abuse, err use. I may give Challenge a ring.
I emailed Donn about it this morning and he got back to me within a few hours which is great. He is mailing me a replacement and I am mailing him the defective tire. I must say I am pretty happy about the level of service I got.
I noticed my Grifo tubulars doing the same thing after last weekend's racing. I aqua sealed them and will see how they hold up this weekend. This worked for my brother's Grifos last year and they've held up so far (maybe 6 races including the brutal day at Nationals). Great to know they back up their product though.