I changed my old tires 235/40 r18 96y (Pirelli Pzero) with new 245/45 r18 96y (Bridgestone) on my s320.

difference:
velocity: 250 km/h (old) 210 km/h (new)
consumption: 7,6 litres / 100km (old) 10,5 litres / 100 km (new)
price: nearly double


now it seems very slow


why?
is it normal?

 

you increased the overall diameter by about 1.5 inches, so the car will have a harder time taking off because of the size and slightly heavier tire weight, your speedometer could be slightly off, and fuel consumption will get worse because more power is needed to keep the car in motion.