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Maybe you can enlighten me. Thanks, I look forward to your reply...
Happy Motoring!...Jim'99[/QUOTE]
Hey Jim,
Below is text from BMW Owner's Manual. from Owners' Circle portion of BMW web site. You can read how it works and the "level of accuracy" obtained.
As I previously said, all vehicles with ABS have the capability to detect rpms on each wheel. There is an electromagnetic sensor on each wheel. The roll radius (not circumference as you mentioned) changes as a tire goes flat and increases the rpm of the affected wheel. The system is apparently accurate enough to detect this change and alert the driver.
Best regards,
Gordie
Austin, TX
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Flat Tire Monitor
The concept
The Flat Tire Monitor keeps track of the inflation pressures in the four fitted tires as
you drive. The system provides an alert whenever the inflation pressure drops significantly in relation to the pressure in another tire.
The check of the tire inflation pressure is based on monitoring the relative speeds of the wheels. A flat tire is detected and reported on the basis of a deviation in certain speed ratios.
Functional requirement
So that the Flat Tire Monitor can learn the correct inflation pressure, please perform the following:
1. Check the inflation pressures in all tires
2. Compare with the inflation pressure table on page 170 and correct if necessary
3. Initialize the system.
Limits of the system
The Flat Tire Monitor cannot indicate sudden severe tire damage caused by outside factors and does not detect a natural, even pressure drop in all four tires.
In the following situations, on the other hand, there can be delays in detecting tire
pressure losses, and even system failure:
When you are driving on snow-covered or slippery road surfaces
If you are using a sports driving style: slip on the drive wheels, high lateral acceleration
False alarms and undetected loss of pressure may occur when you are driving with snow chains fitted
When you are driving with the compact wheel, the Flat Tire Monitor is unable to
function.
Initializing the system
Perform the initialization immediately after correcting the inflation pressure,
after changing a tire or changing a wheel or all wheels. A drive is necessary for this purpose.
Control Center, for principle details, refer to page 16:
1. Before beginning driving, start the engine, but do not drive off
2. Open the menu
3. Select "Vehicle settings" and press the controller
4. Select "FTM" and press the controller
5. Select "Set tire pressure" and press the controller
6. Select "Yes" and press the controller
7. Drive off.
The message "Initializing" is displayed. It takes a few minutes before the Flat Tire
Monitor can detect and report a flat tire. After the initialization is completed, the
message "Active" is displayed.
If a flat tire is detected during initialization, a message appears on the Control Display.
When driving with snow chains or with the compact wheel, do not initialize the system.
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