Hey Mark 123 - I did the same thing and had a lot of the same questions. Here is what I learned and did.
There are a few rental places and the bikes vary. I rented a Honda Phantom (200cc) from Mr. Mechanic because it seemed like the best deal. The bike was OK, it had 7,000KM on it and I put 3,000KM more on it in about 3 weeks. It's light, easy to ride, cheap on gas, and the best thing is that most shops there can fix it and have parts. It was also the rentals that had plates on them since they are made there. I rented mine in November 2005 for 450 baht a day for 3 week term. I had to chat a little with this sensuous yet shrewd lady named Gung (that means shrimp) but she trusted me I guess. My read on this woman is that she gets whatever she wants. I also bought the insurance (that made my rental price go from 400 to 450 a day)
The Phantom is OK, it has a rack on the back and is fairly comfortable to ride for a few hours then your ass starts to hurt. Ride it for 7-9 hours and your ass goes numb and your balls start to sting. Use that as a guide for comfort. It's not an off-road bike at all but it will make is safely through the bad spots. It will cruise about 90KMh max if you don't want to melt the engine and red line at about 120KMh, but if you spend a lot of time in the mountains like I did that's plenty fast. I estimate I was only able to average about 60KMh with stops to eat, the hills, construction, etc.
The Mr. Mechanic agreement states they will refund any repairs you have to have made to the bike that you don't cause up to 5,000 baht. I had to have the rear brake pads replaced in Mae Sa Long on day 3 of my trip but it only cost me 150 baht parts AND labor at the Yamaha place there. Really cheap about $3 US!!! Well, Mr. Mechanic gave me back the money anyway, just like they promised, just save the receipt. I was very pleased with the service there.
I have a nice Nolan helmet at home but I left it here and bought new helmets just for the trip after I got there. Bobs told me about it. You can get a decent full face helmet there for 900-1200 baht. That way you don't worry about carrying around in your luggage or losing your $200 good one. I gave mine to BobS when I left cuz he kinda has a big farang head for Thai helmets and this one seemed to fit him OK. (LOL, Hey Bob! sa-bai dee?
I hope life is treating you well!)There is a MC shop that sells helmets about 5 min walk east from Mr. Mechanic. They can point you there.
I didn’t give my passport to anyone. Gung at Mr. Mechanic wanted it, but then we agreed that I would pay cash for the entire 3 weeks rental in advance without surrendering my passport and she went for it. I left them a COPY of my passport and an imprint of my credit card that I drew a line through and wrote ----0----- and "for security purposes only" in the amount spot. Try and charge that! They took it. And when I returned the bike in good condition they gave me back all the original copies just like we had worked out. Other people were there whining because they had to leave their passport, but I paid cash and money speaks the same language all over there world, no translation required!
If you try and reserve a bike now how will you know if it's a good one? They have their own standard as to what's good and bad, and it may not match your own. You won't get to pick one out that way and if they reserve you a crappy one you will be disappointed. I used to sell cars and people would call on the phone and ask me how much they could get for their car as a trade-in! I would tell them I don't know... why don't you back it up to the phone and step on the gas a few times for me... Use the first day over there to overcome the jet lag and shop around for the bike you want, etc. You probably won't want to ride right after you land anyway.
There are ATMs in every town that will give you as good an exchange rate as the banks. That's what I did. I went to several ATMs at various locations and took out 10,000 baht at a whack. Money goes far depending on what you are doing for a hotel or etc. If you have a debit card with Plus, Cirrus, etc. they are all over.
Where to go - for sure I liked Mae Sa Long loop, Doi Puhka loop, Doi Inthanon and I was surprised how nice the Samoeng loop was being so close to Chiang Mai. In 3 weeks I went from Chiang Mai to Mae Sa long, then to the GT, down to Chiang Khong to Nan, Doi Puhka loop then over to Phayao, down to Phrae, to Theon, back up to Chiang Mai then I rode from Chiang Mai south to Mae Sariang up to Mae Hong Song and back to Chiang Mai from the north. The parts that suck are the super highway but other than that is was all really beautiful country.
I hit about 7 police and military road blocks but as soon as they saw me being a farang with all this gear on and the plates I guess I had tourist written all over me and they would wave me through.
No one that I can tell even made an attempt to steal the bike. Every place I stayed went out of their way to let me park it in a safe location at the hotel or whatever.
Hope that helps. Trust the map and the book. If anything there are more places to stay and restaurants then in the book now. I started looking for a place around 4 or 5 pm. No sense to ride at night cuz it's not safe plus you will miss all the sights going by. Ask to see the room first to decide. Go right to the bathroom and check it. If any part is nasty the bathroom will give it away. Get a prescription of Cipro to have in case you start to get real sick. I bought a soft-sided suitcase at the night bazaar before I left and did all the souvenier shopping at the end.
-Russ