interest rate calculation

I am wondering how Thai banks charge interest on a motorbike loan as the "promotions" at the current Motorshow do not seem like promotions at all

Triumph for example is offering 3.29% but the end cost seems too much.

Do they charge on the original loan amount until the final payment, or the declining value as one pays it off?

Do any Thai lenders on bikes offer what I would think of as a normal rate calculation?