I think you'll be surprised at how easy it is to go beyond 100K. What worked for me when I was pushing my distances out was to break it down into small groups in my mind........as in, ok I've ridden 50 so far, 75 is just another 25 and I Know I can ride 25 easy (in my case it's miles but the same applies). I also planned a route that wasn't too far from home but far enough that I had to really think before bailing coz someone was going to have to come get me if I bailed. (does that make sense?) and laugh if you want - but I Told quite a few of my friends what I was doing, knowing they would ask me if I had made it or not......and that was incentive to keep going when I wanted to quit! LOL