Solving mysteries with my new IR vision "super power"

Something has been bothering me recently.  When I drive home at night in my Chevy Volt and pull into my drive, the motion sensing lights come on.  Since I was driving in EV mode, the 1.4L gas engine/generator was not running - so there should not be sufficient heat signature for the IR motion sensors to "see".  (PIR - Passive Infrared Motion sensors have a white lens that focuses IR wavelength emissions onto a sensor that is able to distinguish warm moving objects moving against a cooler background).

Now that I have a "Super Power" - I can see in infrared thanks to my new FLIR One IR camera that I keep in my pocket. 

I just plug it into my phone and voila I can take still, video and time-lapse IR images.  It's so small - about the size of a keyfob that I now carry it everywhere in its protective case.

So I decided to "see" what was hot.  First I took a picture of the Volt in the 55F ambient weather:

Then I used the remote to turn on the vehicle and pre-warm the cabin to 76F - a luxury that I have always enjoyed in the Volt!  So here it is warmed up 10 minutes later:

You can see a little heat on the hood and driver side window but nothing really hot. (The camera scales the color palette to the whole image, so minor differences are accentuated).

So I drove into town and back, a round trip of about 14 miles in light drizzle. And here is an image taken right after I parked:

The noticeable difference is the tires!  They are 15-20F warmer than ambient now.  If it had not been a cool wet day, they might have been much warmer.  This is enough of a heat signature to trigger a motion sensor.  Mystery solved!

Here's a closer look at the tire:

Parts of the tire read over 75F which is 20F warmer than ambient!  Also the disk brake rotors were up above 85F

It's cool having this amazing IR camera in my pocket (along with my Moto Droid).