Discussions with the VP of R&D of Meguiar's via their detailing forum:
"As most of you know, tire companies build their tires with anti-ozonants build into them. These components are designed to leach to the surface when the tire is under load and in motion in order to protect the rubber from the ravages of ozone exposure. It's ozone that is the main threat to tires, not UV. Ozone levels can vary around the world, but it tends to be greater in and around large industrial cities and at higher elevations. So it looks like Los Angeles and Denver have more in common than they thought! As these anti-ozonants come to the surface and are exposed to oxygen, they turn brown; and this browning of the sidewalls is known as "blooming". Once out and on the surface, they've served their useful purpose and aren't really doing anything any longer - except maybe making the sidewall look less pretty than we'd like. It's a naturally occurring situation ("naturally occurring" as in "it's designed into the tire") and not caused by anything you've applied to the tire. Each tire company has their own recipe not only for the tires but the overall anti-ozonant blend as well. Yes, certain key ingredients are common to most, but it's how their combined, in what ratios, etc that will determine the level of blooming on a given tire.
I can tell you, from personal experience, that when we had 4 different cars at home, each with a different brand of tire, all four cars got the same treatment. That means the same cleaner used on the side walls, and the same dressings used on them as well. None exhibited any cracking that I ever noticed, but one brand of tire showed a noticeably higher level of blooming; ie, those darn sidewalls were always brown. How does this happen when four different brands all got the same cleaning and dressing? It's the tire. That's not good, bad or otherwise, it just is. That's the way the tire was designed. The tires that showed this high level of blooming were Michelins. The other brands were Falken, BF Goodrich and Continental, just for the record. In our VP of R&D's experience, Michelin and Pirelli tires seem to exhibit this to a higher degree than most. Again, that's not good, bad or otherwise, it just is. Both companies make some of the finest tires you can put under your car, no question about it. It's how they construct the tires and what they have in their anti-ozonants that creates this.
Now, fine cracking of the side wall of a tire is due to ozone attacking the side wall. It's quite common for a tire to be taken off a car and the same cracking to be found on the inboard sidewall, the one that never gets any dressing at all. Heck, it never really gets any cleaning either.
So, where do petroleum distillates come into play? Petroleum distillates (let's call them PD's) range from incredibly powerful solvents all the way down to FDA approved lubricants used in food processing plants. That's a pretty broad range. Some petroleum solvents are used in cleaning solutions that will strip that brown off the side of a tire in no time. Some of those might be a bit more harsh than what the tire really wants, or likes. Some might bet a bit deeper into the sidewall and strip out the anti-ozonants that are supposed to be protecting that outer reach of the side wall. Aromatic hydrocarbons, as they're called, are the type of PD's you don't want hanging around your tires as they are very potent. That's not a good thing at all. Meguiar's essentially has two tire dressings with PD's; Hot Shine and Endurance aerosol sprays. But here's the kicker with those - the PD's are basically the stuff that makes an aerosol an aerosol. They're the propellant that moves the ingredients out of the can and onto your tire. They are literally gone in a matter of seconds; they don't stick around on the side wall of the tire.
But what of silicones? Again, silicones encompass a huge variety of materials. We all know that silicones are a bad thing to have in a body shop because any little bit of it getting onto a prepped panel just before paint is sprayed will cause the paint to form fisheyes, a situation where the paint is literally pushed away from the bit of silicone on the surface. But body shops will sometimes use a product called fisheye reducer, which actually contains a type of silicone! Silicone in and of itself, especially in the context of car care products, is an inert ingredient, meaning it doesn't react with anything. Silicones are used to enhance or alter the characteristic of other ingredients - they can make application and/or removal of a product easier; they can help it spread out more readily; they can add gloss. When applied to the sidewall of a tire, they actually prevent - at least to some degree - the ability of ozone to penetrate to the rubber. That means the silicone can actually help protect the tire. Admittedly, this is stretching the point a bit because you're not putting that much product on anyway. Let's face it, we all know that heavy application of a tire dressing is a sure fired way to cause sling, and nobody likes that.
OK, so we've got two aerosol dressings that have a small amount of PD's used as propellants just to get the stuff out of the can. All the rest are water based - gels and trigger sprays like Endurance, M40, Hyper Dressing, Natural & Supreme Shine, etc. All do contain some level of silicone, in varying degrees, but none are harmful to the sidewall of the tire.
To our original poster here, The Dodge, have you looked at the back side of the tires to see if the cracking is there too? Do you have another vehicle with a different brand of tire that you treat the same way but does not have any cracking? Lastly, the area of the tire you describe, close to the rim, is also an area of the tire where there is less flex and movement, and therefore possibly less anti-ozonants being leached to the surface to protect against ozone.
We have every confidence that none of our tire shine products, whether trigger spray, gel or aerosol, will cause any sort of damage to your tires in any way. We have always stood behind every product we make, 100%. That means if you don't like the way it works, we'll give you your money back. It also means that if it damages a surface it's designed to be used on (when used according to directions, of course), we'll take care of you there too. It is extremely rare that we end up buying new parts or contributing to the cost of repairs - not because we fight those claims tooth and nail, but simply because our products aren't causing this sort of damage. That's true of paint care products, cleaners, vinyl dressings, and tire shine products."
