Check if in your RRTPMS.INI if the option "Pressure" is set to 2 when you select PSI as unit of measurement.
The skin provided with the plugin is just to be used as guideline for develope your own skin.
The skin comands for the spare tyre are:
"TMS_ALERT_ST" - Indicates that in the spare tire there is an irregularities.
"TMS_PRESSURE_ST" – Shows the pressure of the spare tire.
"TMS_ TEMPERATURE_ST" – Shows the temperature of the spare tire.
"TMS_BATTERY_ST" – Shows the battery charge status of the spare tire sensor.