Last but not least by any measure, your vehicle must be properly maintained. A vehicle that is not properly maintained can be unpredictable and dangerous. At the very least, it may not respond properly to your inputs and can cause a driver to develop driving habits that compensate for the vehicle’s shortcomings. These habits might then transfer sub-consciously when driving other cars even though the techniques are no longer necessary.
Tires, in particular, are often misunderstood as black, round and rubber. There are entire books written about tires and their unique characteristics. For now it’s important to know that every force experienced by the vehicle is transmitted between the tire and the road on contact patches that are about the size of a postcard. If the tire is damaged or improperly inflated, then that contact patch will be compromised and become unsafe.
Therefore, the first thing to check is the condition of your tires. Observe and measure the tread depth to be sure that the tires will perform as needed for the road conditions. Bald tires can be catastrophically dangerous in the wet. High-performance summer tires can be useless on snow and ice. Tires have wear indicators that let drivers know when it’s time to replace them.
Also note that tires often wear unevenly, even when the alignment is correct. Tire wear is directly correlated to driving style and conditions.
Follow the tire manufacturer’s recommendations on when to replace tires based on expected use. Many online retailers as well as your tire’s manufacturer will have useful information on the care and maintenance of your tires. If in doubt, take your car to the local tire shop to have them look at your tires. It may seem that they are recommending replacement even when it appears that there is adequate tread depth. However, tread depth is the most significant factor in hydroplaning (where the tire rides on a layer of water and loses contact with the road) at freeway speeds. A new tire might maintain contact through puddles at speeds exceeding 80 miles an hour, while a worn tire could lose grip at speeds below 60 mph. Trying to maximize the mileage on a set of tires could lead to a very expensive and possibly fatal accident. Is it realy worth the risk just to get an extra thousand miles on a set of tires?
The next item to check is tire inflation. Typically you will find a sticker on the driver’s side door of your vehicle indicating the recommended cold tire pressure. Cold tire pressure is measured when the vehicle has been sitting for an extended period in a location that is similar to the tire’s expected operating conditions. Keep in mind that driving on a tire will cause it to heat up due to deformation and friction during use. Tire pressures increase when the tire is hotter and drop when the temperatures are cooler. As such, tire pressures also change depending on the ambient temperature. Therefore, tire pressures should be checked periodically and when the seasons change such that cold tire pressures remain the same, regardless whether it’s the heat of summer or the chill of winter.
Tires and wheels should also be checked for balance and straightness. If a wheel is not true, then the car may shimmy when driving down the road. Additionally, an imbalanced wheel and tire will cause vibrations at higher speeds. These both affect a driver’s ability to feel and control the vehicle. An imballanced wheel can also cause premature wear of the shock absorbers due to constant bouncing and vibration. Wheels are always balanced when new tires are installed. Over time, the wheel and tire can become imballanced due to uneven wear. Wheels should be rotated periodically to compensate for uneven wear. This is also a good time to check the wheels' balance.
The vehicle’s wheel alignment is also critical to the driver’s control and feel. When the rear tires are not properly aligned, the car may pull to one side or respond to inputs in unexpected ways, tending to steer more or less than intended. The front wheels are self-aligning to a degree but their relative alignment can also have a negative affect on the vehicle’s response, feel and safety. A vehicle that is properly aligned, will track straight without additional steering input, regardless of whether the vehicle is speeding up or slowing down and when driving over smooth to rough surfaces. There are some cases where high performance vehicles can pull to one side when accelerating so keep that in mind. Furthermore, larger bumps can cause a vehicle to deviate from its intended path whether the vehicle is properly aligned or not. The extent to which a vehicle is influenced by driver or road inputs is an indication of a vehicle’s stability, which is impacted by the wheel alignment. When having a vehicle aligned, ask the shop for a measurement of the vehicle’s alignment before and after the intervention and compare this information against the manufacturer’s suggested values, which may be found in the owners manual or online. Then you can use that information to compare how the car felt before and after the alignment.
Keep up with regular maintenance: oil changes, brake fluid, engine coolant, wiper blades, etc. Keep the engine bay clean and watch for leaks. Never clean a hot engine. Use a mild spray-on cleaner and wash with a gentle shower of water. Do not use high-pressure water, which can push it’s way into gaps and damage electronics, seals and gaskets.
Lastly, vehicles degrade over time: bearings, bushings and ball joints wear out; welds and sheetmetal can crack; bonds and fasteners loosen; metals rust; etc. As a vehicle ages through years and miles of use, it feels less responsive and it can even become unpredictable. The wear becomes excessive when you have to keep the steering wheel moving in order to continue traveling straight ahead. In this case, the car will become unpredictable and even dangerous when turning corners or making evasive maneuvers to avoid an incident.
Some rattles can be benign while others may be catastrophic. A trusted mechanic will help determine which items need to be addressed and which can be tolerated in their present condition. Or the shop will try to fleece you for everything you’ve got! Educating yourself on the various systems of the car and reading online forums can be very helpful to determine common symptoms, problems and solutions for your car. This also helps when communicating with auto mechanics and technicians. You can also find a wealth of information and entertainment listening to re-issued podcasts of NPRs Car Talk. Asking friends and neighbors for referrals to a trusted local shop will also go a long way toward driving with safety and confidence in your vehicle. It can be a mistake to think that the local dealership will provide the best service. Many dealerships are overwhelmed with service requests and mechanics may cut corners in order to increase the number of vehicles that they can service.
The more you can educate yourself on the state of your car and the general construction of all cars, the more you will understand why a particular car behaves in a particular way. Manufacturers and test drivers spend a great deal of effort and time to make cars perform in ways that are predictable and intuitive. As vehicles age, that predictability and performance diminishes. The driver is ultimately responsible for insuring the safety and driveability of their vehicle.