What do Potholes do to Your Car?

There’s no upside to encountering potholes. Brought on in droves as the freeze/thaw cycle weakens and breaks up road surfaces, they become enlarged as each passing vehicle pounds into them and furthers the destruction. In the fluctuating weather that often occurs at this time of year in much of Canada, they’re an unfortunate reality.

Inevitably, you will drive through one. Probably many. Possibly stretches of road that seem to be made of brief sections of pavement interspersed amongst a lunar surface of broken asphalt and water-filled holes of unknown depth and size. They’re largely unavoidable, virtually inescapable, and they have the potential to damage your vehicle and cost you money.*

*Note that while many cities and municipalities have policies in place to compensate motorists for pothole damage, the process can be tedious, the onus falls on the driver to prove the damage was caused by negligence on the part of whomever is responsible to maintain the road, and – based on the City of Toronto’s standards, anyway – the size that the pothole must be before it is even considered an issue may prove surprising. Check out Table 1 in Section 6 of the relevant part of the city of Toronto Act: the minimum size for a pothole to be considered an issue is 8 cm deep, or 600 square cm in surface area. That’s big.

How the Damage Occurs

The damage caused by driving through a pothole begins at the tire, as it’s what first impacts the far side of the pothole. Crushed between the edge of the road surface and the wheel of the vehicle, it gets subjected to violent and very concentrated forces. Modern tires are surprisingly robust, however it is very possible for the sidewall to get pinched between the wheel flange and the ground. The result can be a puncture, a deep sidewall slice that compromises the integrity of the tire, or even cut belts within the structure of the tire. Tires are by far the most likely part of your car to fall victim to a pothole.

The wheel is next in line. Bent lips, fractures/cracks, or even being bent out of round or out of parallel are all possibilities. Some of this damage may not be obvious without spinning it in place on a hoist or mounted on a tire balancer.

The wheel bearing experiences the impact shock from the wheel at the same instant as the wheel. Direct bearing failure as a result of hitting a pothole is extremely unlikely; however, repetitive or severe impacts can crater or flake the chromed surfaces in which the bearing’s balls or rollers run on, leading to premature death, excessive play, or – quite commonly – noisy operation.

Immediate injury to a shock or strut from an impact is similarly unusual, though their mounting points can break in extreme cases. Even so, every motion of the suspension is countered by resistance from those components, which pass oil through tiny holes and valves to create that resistance, a process that generates heat. Besides the expected physical wear, tremendously rough surfaces taken at speed, such as a dirt road or heavily pockmarked highway, can actually overheat the shocks, potentially damaging the seals, eventually leading to oil loss and damping failure. An oily damper is a failed damper, and it and its matching mate should be replaced.

There are a multitude of different suspension layouts, but there’s some commonality between them – all use some kind of bushing or pivot where they connect to the vehicle’s frame or body; all use some form of ball joint, strut mount, or kingpin to facilitate steering; and all can suffer from bent, fractured, broken, or worn out components and mounting points. Regular vehicle inspections are a must, and any unusual behaviour – especially in the wake of a particularly noteworthy impact – should be investigated as soon as possible. The pounding that your average ball joint or tie-rod end receives is astonishing, and in most cases failure will lead – at minimum – to considerable damage to the vehicle and the need to be towed, with the very real possibility existing of a loss of control leading to a serious crash.

Warning Signs of Damage

There are immediate signs to watch for after running into a particularly memorable pothole, especially those encountered at any kind of meaningful speed. Most of the same symptoms also apply to damage caused by skidding or sliding into a curb, ditch, or snowbank, whether there is visible harm or not.

Signs of immediate concern include a shimmy felt in the steering wheel or through the vehicle body that was not present beforehand (often most noticeable at low speed), pulling, a misaligned steering wheel (i.e. crooked when driving straight ahead), or any unusual rattling, clunking, or rubbing noises.

If you observe any of these symptoms, particularly after hitting a pothole, road heave, or suffering an inadvertent impact, you should have your vehicle inspected by a qualified repair shop.

Impacts severe enough to damage a tire or wheel can also damage other less visible components within the steering and suspension systems, so the same advice applies even if a flat tire is the only apparent consequence of your incident.

Minimizing the Consequence

There are lots of factors that influence how much (if any) damage potholes or heavily broken pavement will cause. Obviously increased speed means increased impact energy, but the low-profile tires used on high-end and sporty cars are at greater risk than the taller tires common to trucks and many SUVs.

A recommendation that I make to my customers is the use of a dedicated set of wheels for their winter tires, using a smaller-diameter wheel whenever that option exists; this applies to both cars and light trucks. (Keeping the overall diameter of the tire as close to the original as possible by selecting an appropriate replacement size will maintain speedometer accuracy, clearances, and gearing.)

Smaller wheels mean using (often less expensive) tires with taller sidewalls – more forgiving of impacts – while relatively inexpensive steel or aftermarket alloy wheels minimize the cost of replacement in the event damage does occur. Less expensive at changeover time and eliminating the potential for damage to both tire and wheel during mounting and dismounting, a second set of wheels offers an additional bonus: keeping the original (usually ludicrously expensive) factory wheels away from both prime pothole season and the corrosive effects of salt and anti-icing brine.

In this part of the world, it’s unlikely that you’ll be able to avoid every pothole, but there are ways to reduce their impact on your car and your wallet. Recognising the signs of damage if it should happen can still allow you to minimize the risk of further harm to your vehicle and safety. The pavement should be the only thing that gets all broken up about pothole season.

How to avoid a “wheel” mess. 2/1/2018 10:00:00 AM