I've always been pretty anal about keeping track of mileage on my various cars...just interested. So when I came across this semi trailer hubodometer that can be calibrated for your 15", 17", etc., trailer wheels I bit. It is pretty cool, bolts directly to your rim in minutes and also can be pre-loaded with mileage (like mine, see above anal reference) for $10. The whole thing was just over $100. Thought it was cool and would share with you guys as I suspect one or two of you have car trailers or RVs
I got it at RVeditions (you can find them online), Marv helped me.
BTW, disregard my rusty wagon wheel rims, I know, I know...