I've never tried the marathon Plus...
Frank, it might be worth a try someday. When I used the 700C version of the Plus in goathead country, I found it worked well at warding off the thorns ("little t"; we want to keep the Thorns) simply because the rubbery filler belt is so thick the spines couldn't reach all the way through to puncture the tube -- so long as one didn't lean over too far to the side, as the belt gets thinner away from center. For most use I found they worked remarkably well on blunting goatheads.
The Plus is a
heavy tire, and I found weight of the big, thick belt of rubbery blue stuff did compromise the ride and acceleration over Schwalbe's other tires. It
might be a better net solution over your current thick tubes and sealant. If you go this route, be aware the thick belt can make for a larger diameter in some sizes, so standover can be reduced marginally and you might have to reset your computer. It can make mudguard clearance less, and this along with the sluggish response is what made me remove my 700C versions.
If you really think your current setup is flat-proof, take a sharp sewing machine needle gripped by pliers and slam it against the tire and see what happens.
Exactly what Schwalbe show in testing in a photo on their site to demonstrate the Plus' puncture -resistance. They say...
This new advance in puncture protection is due to the five millimeter thick Smart Guard puncture protection belt made from special india rubber that in conjunction with the tread and carcass brings the total to almost a centimeter of material between the tube and road. "So strong nothing penetrates", assures Bohle technician Markus Hachmeyer. For example a thumbtack will remain lodged in the rubber and cannot penetrate.
A bit more about the belts here:
http://www.schwalbetires.com/node/943 Even with the best setup, a flat can occur at any time if there is air in the tires. Even thick steel-belted automobile tires get occasional flats.
Yep, agreed as to the inevitability. Someday, somewhere, something sharp will have your tires' name on it. The key is reducing the incidence and resultant inconvenience to reasonable levels for oneself, balancing the costs of prevention against the inconvenience of repair.
Best,
Dan. (...who never tires of tire-talk, but feels a little flat when his tires go down)