Caring for the Tires and Exterior Rubber
We all know how much tires and exterior trim that have that satin glow and are deep black in color add to the visual impact of our cars. However the proper techniques and products evade most of us. We've all seen tires that look like a glazed doughnut and paint streaked with the dressing coming off the moldings. And how many of you wish your dressing actually lasted longer than a week? The other factor in the equation is the preservation of the rubber itself.
Left alone, tires and other exterior rubber will fade, crack and eventually lose their mechanical properties through Mother Nature. The first environmental enemy of rubber is exposure to the ultraviolet (UV) light. UV attacks rubber through a process called photo-degradation (similar to the way UV light oxidizes paint). The second enemy degrading tires and other synthetic rubber parts is ozone, a colorless gas that is part of the air we breathe. When ozone combines with UV light, a reaction occurs that attacks the rubber polymers. Add environmental pollutants into the equation, and we have a problem; "dry rot". Dry rot is a million dollar concern for RV, boat trailer and classic car owners that are parked for extended periods (I'm sure you've seen RV's parked with their tires covered).
Early damage may be seen as a general fading of the black color and eventual cracking of the tire sidewall. To protect against this environmental damage, manufacturers add a stabilizer molecule called a "competitive absorber" to the tire polymer. It works by capturing and absorbing UV radiation and converting it into heat to be dissipated. All tire manufacturers have been using the same competitive absorber, carbon black (specially structured particles of carbon), since 1904. Carbon black is a reinforcing filler that is highly resistant to abrasion. It is made from oil and is the reason tires are black. While tires could be made in designer colors (actually, rubber in its natural states is light grey in color), for various reasons including consumer rejection, they are not common. Too bad, because I remember going to a Porsche dealership when I was still in high school and telling the salesman that when I finally "made it" and bought my yellow 911, I would like forest green tires as an option. I still remember the look he gave me, priceless.
The competitive absorbers are sacrificial, meaning eventually they get used up. As carbon black loses its ability to perform, the rubber turns gray. This is one reason that black tires discolor as they age. To further protect tires, manufacturers add waxes and polymers into the tire compound; this blend retards the ozone from attacking the rubber and extends the time before the tire starts to surface crack over a wide range of temperatures. It's no surprise that caustic wheel cleaners remove this protective coating, but an amazing number of rubber dressings also increase rubber deterioration. During a sidewall inspection, manufacturers actually look for damage caused by these types of dressings. Tires flex when in motion, causing the wax molecules to migrate toward the surface. This forms a protective barrier between the air and the tire polymer. A white powder-like coating forms on the rubber surface. This is called "blooming". When tires are parked for extended periods, blooming does not occur and ozone starts attacking the tire polymer. With UV light and ozone working in concert, the degradation is accelerated resulting in drying, discoloration and cracking.
In addition to nature attacking the tires and rubber trim, man has developed his own way to add to that: Rubber/Vinyl Dressings. While the intended purpose for these chemicals was to protect the rubber as well as add competitive absorbers, many of today's dressings do nothing more than provide a short term greasy shine (they are usually clear and greasy similar to baby oil). They are usually a mix of kerosene/mineral spirits and dimethal silicone oil. These petroleum distillates act to strip away the protective waxes from the tires and not only do nothing to protect the surface, but actually degrade it. Dressings come in two flavors, solvent based and water based. As a rule of thumb, solvent based dressings last longer, but the new generation of water based dressing have durability approaching those of the solvent based. If you choose a solvent based dressing, choose one with a highly refined grade mineral spirit; this allows it to dry quickly before it can attack the protective waxes and polymers. Also if choosing a dressing with silicone content, make sure that the dressing contains "good" silicone (of the amino or siloxane functional family). These are "non-migratory" or "dry". And finally, make sure the dressing you choose does not contain formaldehyde (yes, as in funeral home).
Now let's look at how we can maintain our tires and trim. The first step to stabilize the compound and reclaim the original tire luster is a thorough tire cleaning. Select a non-acid ("basic" pH >7.0) wheel cleaner or a natural citrus-based degreaser. Also, use a soft, flexible wheel brush with natural tampico bristles (in case it comes in contact with the wheel surface) to get the full effectiveness of these cleaners. By the way, if you've just mounted new tires on your car, you must first remove the mold release agent or else your dressing won't absorb (this leads to short durability and splotchiness of the dressing). The mold release agent is similar to the wax on wax paper and must be dissolved with a solvent based cleaner followed by a "basic" wheel cleaner or degreaser. Repeat the procedure until the tires are squeaky clean.
The second step to restore the natural luster is the application of a high quality rubber dressing containing UV stabilizers which supplement the UV-protection action in the carbon black. Although exterior rubber requires a very durable dressing, it must not jeopardize the integrity of the compound. In our shop, we use different treatments for the tires as opposed to the rubber trim, we recommend the DyNA Concours Tire Treatment™ for your tires which has all the protective attributes described. Usually, the price of a dressing gives a hint of the quality of the dressing. The tires should have a satin sheen to them when dressed. Also, the dressing should not be slopped on as they do at the car wash with a paint brush so as to sling off all over your car's paint and the poor guy behind you. I can't tell you the numerous times I have gotten a glob of some greasy dressing all over my pants while judging PCA Concours events (needless to say those cars didn't win - I deducted 2 points consisting of ? point for the excess dressing and 1? points for the pants). I recommend applying the dressing with a foam applicator and storing the applicator in a Zip-Lock bag for future use.
On a related note, all of the modern cars with flexible bumper covers and side moldings require a "flex agent" added to the paint to give it flexibility. However, this flex agent causes the painted parts to be more porous. This porosity leads to the absorption of any of the sling-off of low-grade petroleum oil dressings which leads to black stains that are impossible to remove. Even repainting these parts is impossible and they must be replaced. I know for a fact that Cadillac had this issue some time ago and now specify in their manual that they are not liable for that kind of damage. I'm sure other car manufacturers have the same policy.