Big Wheels vs Computer????????

[FSETH]

On a different note, the size of the hub DOES NOT change! You don't replace the hub when you replace the wheel. An X5 will have the same size hub with 13 inch rims to 30+ inch rims. The hubs for all E53 X5's are the same size. The speed at which the hubs (and brakes) spin is determined by the rotational speed of the axle. Just because you got a bigger wheel doesn't mean that your axle is spinning at a different speed.

You are correct. The hub/axle speed will be the same as the speedo regardless of wheels sizes. That is the issue here. Vehicle speed is not necessarily the same as hub/axle speed once the overall diameter of the original wheels and tires are changed. Vehicle speed depends on the overall size of the wheels. Think about it for a minute, hub spped at 50 mph with a 10" wheel would not be the same vehicle speed as a 22" wheel. I don't see how a computer can accurately measure and compensate for different overall wheel and tire sizes unless it knew the exact overall diameter of the wheel and tire which would have to be programmed into the computer or sensors would have to be installed in the outermost part of the tire (the tread) to accurately determine that.