Walden,
The 500E is one car where I would leave the Porsche designed suspension bone stock. The rear suspension is adaptive, playing around with ride height would cause all sorts of problems. If you look at the Eibach application chart you will notice they don't make springs for 500E's. If you look at the Renntech catalog you will notice that they don't offer a lowering kit for the car either. Renntech will do it, but by special order only. (special order = even more megabuck than they already are) Not to mention the thing is significantly lower than a normal E-class to start out with, if you go much lower you wont make it over speedbumps, driveways, etc. (speedbump clearance is ride height + wheelbase and this is a 4-door sedan we are talking about not a tiny two-seater) First time you rip the muffler or resonator off it will be big $$$. I'd put the cash towards a top of the line radar/laser detector to help you stay out of trouble that the massive power will get you into. (EG) Tires and wheels you can change somewhat but expect to pay double what you would for any other benz application just because of the rarity of the offset needed. Combined with the fact that only ultra high-line companies make wheels to fit(AMG, BBS, Lorinser, Carrlson, etc) Tires...I'm not sure what would fit. You can try contacting Tirerack, their professionals would be able to tell you for certain. I know for a fact that 235/50/16 fits the stock wheels and works VERY well. It is sort of a rare size but it stands to reason that 235/45/17 would also fit. I also know that 245/50/16 will NOT fit despite being almost exactly the same rolling radius. I'm not sure if it is the section width of the tread or it not fitting on the stock wheels... Again, call the pros at Tirerack. They have detailed info when it comes to specific aftermarket applications. There are two other variables you can mess with before you go and buy way wider tires/lower profile rims. First, buy the stickiest damn tires you can find in the sizes closer to stock. (235/50/16 Michelin Pilots are one option I am considering) Second, when you get those ultra-sticky tires run the pressure up close to max cold-psi. Just keep the same ratio that the stock setup is(29/30 if memory serves) So if the max pressure for that tire model was 44 lbs(cold psi) then you could run 42/44 f/r for a more aggressive handling setup. Just a suggestion....Lee