The diameter of the wheel is identical. The grip is different throughout the wheel.
Towards the top, the wheel is shaped almost in an oval, so it feels much different. As your hands slide down to 10 and 2, the increased bolstering is really nice.
Continue down the wheel, and where 9 and 3 is, the grip feels really comfortable. No doubt from the softer material. My favorite grip for long drives. Really comfortable.
At the bottom, the flat portion is significantly bigger than stock. Quite a bit bigger than the rest of the wheel.
Driving it feels excellent as you transition between different hand positions and thickness.