ML 250 (1922cc & 200hp) in HK comes with 17" wheels set. The sales manager told me I am only allowed to upgrade to 18" wheels but not 19" wheels. Reason being the engine is smaller and it would not be efficient to roll a 19" wheels set. Is there any truth to that pls?

 

That's BS. 19 is standard for ML250 in many countries (for example Europe).

Additionally, 19in wheels are bigger but the overall tyre diameter is the same, so it does not affect the crankshaft to wheel ratio. The only thing that could matter is if the rim is wider and requires a wider tyre. You would lose a little in gas mileage.

 

In the US you can get the 250 with 18", 19" or 20" wheels. The dealer is full of it.

 

My base model ML250 has 19" wheels. In fact thats the smallest they come with here is OZ.