Larger/Taller tires can affect the shift points of the transmission due to the change in transmission output shaft speed. A taller tire in essence raises the final drive gear ratio slightly. So shift points would be slightly raised due to a higher MPH speed on the speedometer when installing a taller tire.
But the indicated speedometer speed does not control shift points.
From the FSM: wrote: OUTPUT SPEED SENSOR DESCRIPTION
The Input and Output Speed Sensors are two-wire magnetic pickup devices that generate AC signals as rotation occurs. They are mounted in the left side of the transmission case and are considered primary inputs to the Transmission Control Module (TCM).
OPERATION
The Input Speed Sensor provides information on how fast the input shaft is rotating. As the teeth of the input clutch hub pass by the sensor coil, an AC voltage is generated and sent to the TCM. The TCM interprets this information as input shaft rpm. The Output Speed Sensor generates an AC signal in a similar fashion, though its coil is excited by rotation of the rear planetary carrier lugs. The TCM interprets this information as output shaft rpm.
The TCM compares the input and output speed signals to determine the following:
• Transmission gear ratio
• Speed ratio error detection
• CVI calculation
The TCM also compares the input speed signal and the engine speed signal to determine the following:
• Torque converter clutch slippage
• Torque converter element speed ratio
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