Tiptronic
The CLK 350 engine matched to the 7-speed needs some encouragement with the tiptronic to stay in a better rev range; the shift points are set more for economy than performance.
I have only driven my car for 40,000 miles so far but the shifts in tiptronic mode are very gentle and will not let you downshift early so I doubt there is any long-term drawback to using tiptronic.



