i went to a tuning shop and they told me that the car can be lowered by changing valves from the dealer. there is no need to change shocks and springs? is this true? if not how is it possible to lower the SL with 19s.

 

The car (SL500) has adjustable ride height already, as standard to raise the car in two increments from the standard ride height for low speed bumps. It will also lower itself at speed to improve the aerodynamics and reduce axle lift.

The suspension on this car is in a completely different league from other cars and well beyond the capabilities of a tuning shop whose staple diet is some 60's Dodge pickup.

You can get the ride height parameters changed so that the car is lower at rest (other people will tell you how, I haven't done it on mine).