You may notice that not many 20" folding bikes are made for off-road. Let's figure out why, shall we?
Originally Posted by Gotte
I'm tempted to do my next tour on a 20" folder. Am I right in thinking that 20" wheels are less prone to spokes snapping, and easier in gravel/dirt?
In terms of wheel strength: theoretically yes, practically no. Any well-made wheel is going to hold up to most touring conditions; any poorly made wheel is more prone to bust a spoke. Plus, any wheel can get damaged in transit.
In terms of gravel and dirt: Smaller wheels generally provide a harsher ride than 26" or 700c. You can easily compensate by using tires that are wider and/or have a lower PSI. You'll have a minor performance penalty, but one that is totally negligible in a touring context.
In addition, the drivetrain on a 20" wheel is going to be much lower to the ground than a 26" or 700c wheel.
Additionally in addition,
most folding bikes have non-diamond frames with a big hinge in the middle and very tall handleposts (e.g. Dahon and many others). This has neither the structural strength nor maneuverability associated with, say, a BMX bike. Not a great choice for extensive off-road use.
If you are occasionally
hitting gravel and dirt, you'll be fine with a 20" folder; just keep an eye on the drivetrain. If you plan to spend most or all of the time playing in dirt (e.g. Katy Trail), there are a handful of 20" folders and collapsible bikes made for offroad use. Or, I'd look into an S&S coupled bike like the Surly Traveler's Check.