Hmmm .. Its a bit of a grey area. You are by law told to carry ID, this is left to the discretion of the person or organisation checking your ID wether it extends to a passport.

Sometimes they can demand that you return to your lodgings while your transport or spouse is held hostage at the side of the road, other times more than happy to accept a photo-reduced copy of your passport data page sealed in plastic .. its not a bad thing to copy your entry stamp and TM6 Arrival card and keep safe should something get lost or stolen. its only 1/2B - 2B per copy here.

On the whole if your on a bike, they are more concerned that you are road legal. Most of the time, if you have a helmet and can see you are western they will ask where you are heading and sometimes ask for a licence or an IDP.

You can find some reliable info here .. Carrying Your Passport in Thailand

Also bear in mind, its illegal to ride with a tinted visor here. It's never a problem but if the guys are on the look out for some tea money, it could be an issue. If you approaching a checkpoint, just lift it so the authorities can see your face.

Hotels .. I never carry my passport, just use a driving licence to check in, again, another grey area, but the hotel should take a copy of your data page and TM6 to file a notification to the immigration office.

Do you want to leave your passport behind as a deposit ? Hell no !! There are plenty of reputable bike shops in CM who would be happy to take a copy of your particulars and a small cash deposit. Just don't do it.