I have a few friends that used to work at Ford. They tell me the blue dot (green dot on some fords) are the heavy point on the rim. The tires have a paint or decal on them also to indicate the heavy part of the tire. The person installing the tire should line-up the dot with marked spot on the tire. If no dot exists on the rim, the dot on the tire should be lined-up with the valve stem.
I walked around the Ford dealership's lot (when I bought my (now sold) '03 Mustang Cobra) and sure enough, all of the green stickers on the tires were lined-up with the valve stems.
Something interesting -- my wheels all had blue dot, no tpm. After my day was ruined by a drunk using the MO for a stopping device, one wheel had to be replaced. New wheel from Nissan did not have blue dot.
I understand it's for balancing as well, but lining up the heavy side of the tire with the heavy side of the rim makes no sense. If anything, I could see lining them up, if the blue dot was the light side of the tire lined up with the heavy side of the rim. This would reduce or maybe eliminate the need for weights (in some cases) when balancing the wheel.
The other thought was it was a warning label to Smurfs. Either that, or they're using Smurf labour and it's a thumb print.
Here's my theory... There's a lot of markings on cars. I always thought these markings were to help the dealers identify if parts have been tampered with, adjusted or modified... (so it's easier for them to say you voided the warranty...) From what I remember, there was a blue dot on the wheel that lined up to a marking on the tire. Also, if you peek under the rear suspension, there are markings near bolts and washers. I could be really wrong but that's my theory with the markings in cars
The blue dots are just practical jokes. Somewhere in Japan there's a group of factory workers laughing their asses off because we're so perplexed by them. Personally, I like them and plan to keep them. Stop bashing the poor little dots!!!:4: