How difficult is this trip?
The trail riding is not technically demanding, but sustained riding over distance, and can be tiring, especially in hot temperatures (up to 40 degrees C after February). You don't need to be an expert off-roader (I'm not), but should be able to keep up 15-40mph over hard packed or loose trails for 30 or 40 km at a time.
Falling off from time time is permissible, but don't make too much of a habit of it, as we don't want injuries. (photo is of Dave, posing for a "drift" photo and making a pig's ear of it!!!)
I've done this same trip over a dozen times now. Each time using slightly different routes. There are maps, and although these are quite accurate, there's lots of opportunities to get lost due to unmarked junctions, and extra bits which don't always appear on the printed maps. There are very few sign posts, and most of these are in Thai script, so make little sense to non-Thai speakers. People you approach for directions will not always understand the concept of a printed map, but can usually point us in the right direction when asked.
However, we can, and do, get lost from time to time - it's all part of the adventure. Bit by bit, I've learned all the way markers, but I need to go back every year to keep up my knowledge! The trails sometimes change from year to year, often due to Monsoon rain damage.
Friends / partners are welcome to spend some time as pillion passengers, BUT, I don’t recommend carrying a pillion passenger for extended periods off-road. A pillion is fine on the road sections, and just for short distances off-road. But don’t try and carry a passenger all day off-road – it’s extremely tiring and uncomfortable for rider and passenger and not recommended. We’ve done it once, and it really isn't pleasant!
I still stand by my original statement and say this is not ideal for pure off-road novices unless you just happen to be endowed with some natural talent. The trails are usually quite straightforward – just unsurfaced roads for the most part, but don’t do it unless you’re a pretty confident individual, or have done a bit of dirt riding before. With one or two exceptions (e.g. Shaun – who was an successful Enduro competition rider, and shamed all of us with his divine ability), most riders have been confident beginner, to intermediate level trail riders.
There is of course, the option to stick to surfaced roads, and you can choose a road bike if you want for the tour – but then you’d really be missing out on most of the fun.
To try and quantify what we encounter...
Compared to England, quite long stretches of unsuraced trails. Sometimes riding 30-40km at a time off road. The hardest day is only 160km (3/4 off road) and sometimes we do a 85km off-road stretch. Easy? Yes, fairly. If you want harder, go to Morocco.
Some stream crossings, although nothing too major.
Some of the trails are rutted. Some ruts are caused by other transport (like 4x4s in UK), but are more likely to be rivulets caused by rainfall. In general, the trails are far less rutted than UK Green Lanes.
On some days we'll encounter reasonably steep gradients. Either uphill, or downhill, the surface may be loose sand, dust or gravel, or sometimes even wet clay. You need to keep the power on going up hill, and leave off the brakes going downhill.
Compared to the UK (or Africa), we DO NOT generally encounter massive rock steps, deep sand (dunes), long sustained deep tractor ruts, peat bogs, or too much slippy mud over the dry Winter season.