I'm also trying to figure out the same thing. I want to go as big as possible without much negative effects. I'm using eibachs too...1.5". If I can get something close to a B15 tire size, I might go with 16 or 17.
Right. I gave those numbers because i was thinking about the speed meter accuracy and minimum negative effects. If you ran 215 and didn't have any problems, i was probablly wrong then. Experience is everything.
To calculate appropriate wheel and tires, you need to calculate stock wheel/tire diameter so you have a baseline for maintaining speedometer and odometer accuracy.
Wheel diameter + (tire width*aspect ratio/100*2)/25.4.
Wheel diameter is in inches, tire width in millimeters. 25.4 converts the tire height from millimeters to inches. Aspect ratio is tire sidewall height divided by tire width. One tire's measured height and width don't necessarily match a different manufacturer's measured values for the same size tire, so exact comparison isn't possible, but it's close enough.
195/50-15 = 195 mm tire width, 50 aspect ratio, 15 in rim diameter.
Use a spreadsheet to generate a matrix of possible sizes and select those that deviate less than 2% from stock. E-mail me direct and I'll send you mine in Lotus 1-2-3 format as Excel sucks!.
Eibach springs are good, there great in fact. Most of the 24 Hour and American Lemans race cars use them, so you know if there on high dollar production super cars then they have to be good! Hell Eibach has been around for a long long time. H&R is aweome as well, again being used on high dollar super race cars such as the Mustang Saleen S7R so you know there quality too. It just seems that there are more Eibach applications for our cars than H&R. But maybe H&R is stepping up on our applications too.