Wheel rim corrosion
Most cars have alloy rims nowadays, and corrosion of aluminum can cause tyre issues
By Louis Rumao
A few days ago, I left home for a 300-mile drive in my 2011 model vehicle, going from Detroit to Chicago and expecting to reach my destination in the usual 5-hour drive. About 5 miles away from home, tyre icon popped up on the instrument panel, indicating some tyre issue.
It came as a surprise, since before leaving home I had done my routine vehicle walk-around and everything had looked normal. Luckily, a petrol pump was nearby and after pulling in there, I visually inspected all tyres and did not see any obvious problem, especially because radial tyres “look” low even when properly inflated. So, I just decided to add some air to all tyres. However, In these days of “self-serve” petrol pumps, air is no longer free – typically costing $1 for a 5-minute compressor usage. Anyway, I got all tyres inflated to the recommended level and was on my way.
The tyre pressure monitoring system (TPMS) was mandated in 2007 by the US government in response to a surge in accidents due to under-inflated tyres, via the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act. There are two types of TPMS – Indirect and Direct. An indirect TPMS does not read tyre pressure, but relies on wheel speed sensors that are part of anti-lock brake system (ABS). When a wheel starts spinning faster than the other wheels, either due to under-inflation or excess wear, the ABS computer calculates that the tyre is under-inflated and alerts driver accordingly.
Disadvantage of this system is that it needs to be reset each time a tyre is inflated and after routine tyre rotation. Direct TPMS uses pressure monitoring sensors within each tyre and, if tyre pressure is lower than it should be, transmits directly to the instrument cluster where a warning icon is illuminated. This operates on a battery that typically last for about 10 years.
All drivers need to remember that even though a TPMS can deliver accurate alerts when properly maintained, it’s not a replacement for routine tyre maintenance such as visual inspection, air pressure checks and tyre rotation – it is just another item in our maintenance toolbox for vehicle safety
Back to my car, the TPMS icon was illuminated again after a week, indicating a slow leak in one or more tyres. A pressure check indicated that one of the front tyres was slightly under-inflated. So, it was time to get professional help and I took the vehicle to a local tyre service center – Discount Tire.
Discount Tire, a privately-owned company, grew from a one-man operation in 1960 into the largest independent tyre and wheel retailer in the world, with over 900 outlets in 28 American states. Its growth has been largely attributed to the company’s focus on reasonable prices, customer service, and its satisfaction guarantee. I had used this outlet in the past, and when a service specialist entered my phone number in the computer, all my past transactions came up. When I told him my concern, he delighted me by saying that at Discount Tire all repairs are FREE! He then went out to look at the tyres and came back with the following:
Your tyres were made in 2010. We recommend that tyres be replaced after 6 years.
Your tyres have 5/32” tread remaining. You need to replace tyres when tread depth is less than 4/32”.
The problem wheel was removed and not finding any obvious cause of slow air leak by visual inspection, it was dunk tested, when a tiny leak at the bead was noticed. The tyre was dismounted from the wheel, where tell-tale signs of corrosion were observed at bead-rim contact spot.
Bead seat corrosion
Bead seat corrosion is identified by what appears like blistering of the wheel finish, or powdery residue causing a rough or uneven surface. Corrosion happens to be the worst right at the sealing bead because of a phenomenon called crevice corrosion. Below is close-up of bead seat corrosion on an aluminum wheel that was sufficient to cause a slow air loss.
If corrosion is found on the wheel bead seat, the affected area is measured. When the length of the bead corrosion is more than 4 inches for vehicles with less than 20,000 miles, or more than 8 inches for vehicles with higher mileage, the tyre service technician may suggest that the wheel should be replaced. Otherwise, the corroded area is sanded and the repair area is coated with a bead sealant. A reputable tyre service outlet will ensure that the repair is done correctly. Drivers need to be aware that a slow tyre air leak on a newer vehicle with cast aluminum alloy wheels is most likely due to porosity in the casting. Again, this type of defect can be eliminated following wheel supplier’s recommended procedure. For rims with high degree of porosity, it may be safer to replace than repair, as porosity can make the rim weak.
Discount Tire repaired my leaky tyre for free, thus ensuring that I will go to them when I need future service or tyre replacement.
All drivers need to remember that even though a TPMS can deliver accurate alerts when properly maintained, it’s not a replacement for routine tyre maintenance such as visual inspection, air pressure checks and tyre rotation – it is just another item in our maintenance toolbox for vehicle safety.
(Appeared on February-March, 2018 issue of Tyre Asia)