I took my motorbike test in Cmx in January. You need a T30 from where you are staying. Take that to the immigration office near the airport along with a medical certificate from a local hospital or clinic where they will take your blood pressure and ask if you have any medical issues, cost about 150 baht. At immigration you will pay 1000 baht to collect your paperwork the next day.
Book an appointment at the test centre,near the airport ( I had to wait a month for my appointment, but that was high season)
On the day of your appointment, take your paperwork and passport to the test centre where you will watch a safety film with English subtitles all morning. Then come back in the afternoon to take a multichoice test on a computer where you need to get 45 out of 50 questions correct. If you fail, you go back the next morning to retake the test, if failed, back in the afternoon to retake, rinse and repeat until you pass. It took me 3 attempts. Then you watch another half hour safety film and the motorcycle people go off to drive around and the car drivers likewise. If you pass, back into the building for photo and issue of licence, cost 125 baht.
Multi choice questions same for motorbike as car.
You need to look online for mock test questions before you take the test, otherwise you will certainly fail, as you need to know some of the signs are written in Thai, plus speed limits in Bangkok/ Pattaya etc.
The licence lasts for 2 years and then can be renewed for a further 5 years.
Thanks for the quick reply. The only snag with a border hop would be I could only get a 30 day extension, so a total of 90 days, not the 120 days I need. Unless i've missed something?