I just wanted to give something back to the Thai Visa community who gave me advice beforehand and share my experience of doing a border run to Mae Sai from Chiang Mai.
A couple of weeks ago my 60 day+30 day extension SETV in my British Passport was getting close to the expiry date. I decided I would go across the border at Mae Sai into Myanmar and back and do the journey by scooter. I've been an enthusiastic biker for years riding numerous big bikes but here in CM I only have a Yamaha GT 125 that does 95-100 kph flat out.
I left at 06.45 and I was having coffee in the centre of Chiang Rai by 9.30, stopping for gas 3 times along the way. It was 187km by my odometer and most of the time I was doing around 85-90 kph in Lane 1, but there was a several km stretch of roadworks 45km out of CM. I hardly bothered with the cycle/scooter lanes as I was travelling with what traffic flow there was and during the journey only 4 cars/minibuses passed me. There wasn't much traffic going in my direction at all. If I needed to overtake I would use lane two rather than the narrow cycle/ scooter lanes as undertaking is dangerous in this lane, especially as on left hand bends, as vehicles ahead of you drive into it. They also straddle lanes/double yellow centreline on right handers too so its important to anticipate this when overtaking!
I had one experience where I have over taken some slower moving traffic which was in lane one. I overtook in lane two and fortunately for me saw a car travelling at around 120kph in lane 1 which literally flew past me. Having done a lot of my riding in the UK and New Zealand, its not something you expect to experience and I was lucky that I had the forsight to check my mirror before slowly drifting back into lane 1 otherwise I don't think I would be here now typing this!
The ride to Mai Sae was another ~65 km and took me 75 more minutes. Once at Mae Sae I rode just about to the end of the road where the bridge crossing is and parked at the roadside.
The border transition was easy. Just a quick pass through the Thai border passport control and stamp out, before going into a Myanmar Passport Control office in my case to hand over my passport and a clean crispy pre ironed 10 USD note (or 500 Baht). You get a receipt for your passport. I walked across the river bridge, had a quick wander around the market type stalls on the Myanmar side before coming back, then collecting my passport from a Myanmar Immigration window on the other side of the road. I then proceeded to the Thai border where I picked up a TM6 form from a booth, completed it and then presented it at passport control where I had my photo taken and got my British Passport stamped with a 30 day Visa Exemption. No money was needed and I didn't have to show proof of onward travel or bank account funds. It was a straightforward easy process which took no more than 10 minutes in total. It was my first ever land border crossing out of Thailand and I belive that you can do two a year via a land border to get a 30 day exemption.
I after getting some food I decided to head back toward Chiang Mai the same day and go to Chiang Dao but 2 hours into the ride I got a puncture and lost my passport along the way when I had stopped to take my phone out of my pocket. FML!!! So it turned into quite an eventful experience! Long story short, I got the tyre fixed and found my passport on the roadside back towards Mae Sai and stayed in Chiang Rai for the night before doing the return journey the next day.
Would I do the journey again by scooter? Most certainly. If you are experienced riding motorbikes and enjoy it, then it's great and I found it easy to be honest. I didn't have any butt aching from the ride and apart from the one experience which I described with the speeding car, I felt no less safe than I do riding a motorbike/scooter day to day. Next time, I would do the journey there and back in one day I think. I did wear a decent helmet jeans, shoes and a long sleeved top to give me some protection from throwing the bike down the road. It did feel a bit cool first thing and at higher elevations. I didn't have a problem getting up the hills and there weren't that many. Only one took my speed down to about 55kph.
In conclusion, if you like riding bikes, have some road sense, eyes in the back of you head, treat everyone on the road around you as an idiot and anticipate and plan for the unexpected, then do it. I think it cost me around 400 Baht in gas and I enjoyed the ride.