Originally Posted by pacificcyclist

It will be very rough even for a 20" Bike Friday NWT equipped with a long travel suspension seatpost (you NEED IT). I tried it about a decade ago. My Dahon Mu SL with Big Apple tires, a Pantour front suspension hub and a Thudbuster would be I consider comfortable enough but a bit short of my Masi CX with fat 700c tires bike in these Yukon or any FSR (Forest Service Roads). Otherwise and unless you're really young and can take a significant amount of abuse on your shoulders and legs by standing and riding at the same time, you will be significantly slowed down (smaller wheels have to negotiate rocks the size of boulders compared to bigger tires). The best bike for the comfort in terms of touring with it and is folding is either the Bike Friday Air Llama or the Dahon Jetstream or any full suspension. Running bikes off-road require both wide and fat tires to give you good traction and pneumatic suspension (comfort) and enough flotation so your tires don't sink too much into the mud/dirt, unless you prefer to do a lot of walking and standing and pedaling. It's also hard on your arms as well.

Nothing wrong with the Bromptons, though its steel frame will not save you from the jolts you'll get from the dirt roads. Bigger circumference tires will give you more comfort in off-road situation irregardless of suspension; hence a 29er mountain bike rides nicer than a 26" bike.