We live in a hilly area, and the local council sees fit to install numerous speed bumps on the roads here. When driving the Merc over these speed bumps at anything above a walking pace the front suspension bottoms out, and gives a most unpleasant 'thump'.
Australian model GLC 250 here, with the AMG Line package installed. 20" inch Bridgestone Duellers. In Oz the 3 suspension variants available are, base model steel springs, AMG Line steel springs (slightly stiffer than base model), or ABC Air springs with variable damping, as an upgrade option.
On my initial pre-purchase test drive, I deemed that the base model was a little too soft to my liking and the AMG line car was better. Decided not to go with ABC, due to complexity and possible failure point.
Firstly, let me say that I am very happy with my selection of the AMG Line 'sports' suspension. However, just on the odd occasion now and then, I experience the same bottoming out of the suspension. This can occur on the very abrupt speed bumps, (Shopping centre car parks, I am looking at you!), or on a very bad deep pothole (not uncommon on Oz secondary 'roads').
To my view this is due to a combination of things: Run Flat tyre (stiff sidewalls), low profile tyre 255/45 R20, not enough suspension travel, not enough spring rate and damping. ( have experienced all 4 wheels bottom-out on 3 occasions ...not pleasant)
Also the bump stops appear to come up very harshly!
99.9% of the time the suspension behaves very admirably...so I am thinking the springs rates and damping are not too bad.
The key factor I think is the Run flat tyres and the inherent design of very stiff side walls.
If this is a real concern in your area of travels, I would advocate, changing to 19"rims and higher profile standard tyres (not run flats... I will be changing to non Run-flats when current Bridgestones need replacing, but keeping the 20" rims)
Talk to your dealer about a low cost or better a no cost swap!! (no harm in asking)
Also check your tyre pressures. Placarded 32psi is too low. Dealer handed my vehicle over with 42psi ...too high. I have found 35-36psi a good compromise between comfort and tyre wear pattern.
Of course, better road building/maintenance skills in our country could negate all of above!! Ahhh!! ...….but I jest!!!!!