I've done D2R2 twice and would do it more often as several of my riding friends have done it each year it's been run, but the timing is usually when we're away on family end-of-summer vacation. Ditto to what Anton says in terms of lots of climbing, lots of dirt, great food, great scenery, and lots of climbing. And then there are the riders who do the 100-mile ride on a fixed gear and skinny tires. Amazing.

My first D2R2 was the 100k ride, and it was in the low 90s that day. After the first real climb, I thought I might just curl up and die right there, but after a good rest stop and some re-charging, I was good to go and the rest of the ride wasn't too difficult. This last time, I intended to do the 115k route, which had over 8500 feet of climbing. After 40 miles and about 4500 feet of climbing, I was extremely cooked, cramping up like mad, and bailed on the longer ride after the lunch stop (though I went back along the Green River road, which is gorgeous). That first ride I was on my Kogswell with 38mm x 650b tires. This last one I was on my RB-T with 38mm Continental cross tires. If I do it this year, I'll again take the RB-T (but this time I'll make sure my FD works under load to shift on to the small ring--that was a problem).