when i bought my SLK rims they had the 205 55 16 tires on front and the 225 50 16 tires on rear. They were WAY TOO BIG for my 190E sheet metal. Dont know about 55 series tires on 300E, seems large to me but I prefer the low profile look. the 205 50 16 looked great on the 7-spoke rims on the 300E IMO. just my $.02