I have a 94 C 220 that I want to put 18" rims on. What negative effects if any will it have on the car?

Switching from stock to a plus 1 or plus 2 fittment will always be a ride vs handling issue. Just keep the overall rolling radius the same. It all depends on your personal priorities. Lower profile rubber and stickier tires will handle better. They might ride more harshly, generate more noise, or wear quicker than stock as well. Driving style and specific tire choice has more impact on longevity than any particular size difference. Check this site out to browse some choices. http://www.tirerack.com Best of luck, Lee

I do not advocate the use of oversized tires and wheels because of diminished ride quality and rapid tire wear. The larger wheels and tires will change steering angles as well. Good luck with the swap, but from my limited experience on this subject and my reservations concerning after market parts for this, I cannot help much.

Good luck and visit us again.

VICTOR.
THIS IS WAY TOO MUCH WHEEL FOR SUCH A SMALL CAR! TAKE A LOOK AT THE AMG C36/C43
CARS THEY ONLY USE 16 OR 17 WHEELS & HAVE SPECIAL EQUIPTMENT SPRINGS & SHOCKS. TRY USING 16" WHEELS LIKE THE NEW SPORT MODELS USE, THE CAR WILL RIDE LIKE IT WAS DESIGNED TO.