sstorkel

Distance is pretty easy to handle... if the ride is flat. If you can ride for four hours at a moderate pace and do it two days in a row, you can probably ride all day at that same pace. That's the rule I used when preparing for my SF->LA tour and it worked out very well for me.

Climbing is usually the bigger challenge. I'd suggest making sure that you've done training rides that include at least 70% of the elevation gain you'll expect to see on the ride. For example, if your ride will have 4000ft of climbing make sure that you've done rides that include at least 3000 feet of climbing. If there are any long, extended climbs if might not be a bad idea to pre-ride them, if possible. Most of climbing is mental, so having knowledge of the climb and being able to pace yourself properly is an advantage, I find.