Nearly all rental bikes here are unregistered.i can't believe you would be insured in any way.The rental shop has your passport and you can be sure they will get any money owing to them and more if you damage the bike.What happens if you have injured a Thai national or his property? Also the rental bikes seem to be fairly well shagged with bad tyres and brakes.So you often have a fairly inexperienced rider on a dangerous bike riding in dangerous conditions with no insurance whatsoever and his passport usually lying in an unlocked drawer in a shop.And another thing,rental bikes are nearly the same price as renting a fairly new car which carries first class insurance.You can get four of five people plus luggage in a car and you are out of the sun.Why not hire a four door pickup and you could put a few bikes on the back.Then drive somewhere and ride a bit off road.I love bikes and have ridden them for years but I would really urge people to think long and hard about the realities or renting and riding here.I often see tourists wobbling up the road on their rental bikes complete with ill fitting helmet pushed back on their heads and a nice pair of worn out nearly flat tyres.it really does worry me and I would never ever recommend renting a bike here.