Suspension inspection: your car is riding on it

BY Jim Kerr. Apr 22 04:00 am

A recent trip to the Far North took me over some extremely rough roads littered with potholes, broken pavement, washboard gravel and unexpected dips and dives. The last 200 kilometres of road were equal to the toughest of any of the auto manufacturers’ suspension test tracks and placed more stress on the vehicle in that short time than you would likely place on your vehicle in a year of driving in the city.

As touh as modern suspension systems are there is always the possibility of something bending, breaking, shifting out of position, or being driven to the point of wearing out. Out of sight, seldom glitzy or shiny, and subject to dirt, moisture and impacts, suspensions are often a forgotten part of an automobile. To keep your vehicle in safe driving condition, the suspension should be inspected as part of regular vehicle maintenance. Spring is a good time to have this inspection done.

Getting a wheel alignment is a good way to have the suspension checked. During an alignment, tire pressures are corrected and the steering and suspension joints are checked for wear or damage. The auto manufacturers and aftermarket parts suppliers print specifications for the maximum movement allowed in a suspension part. If you have any doubt about when a suspension joint should be changed, ask to see the inspection procedure and specifications. Good alignment shops always have this information.

Leaking shock absorbers or struts should be replaced. An oil film and dirt on the outside of a shock or strut is considered normal, but oil dripping from the unit indicates it will need replacing. Heavy-duty or premium shocks are far superior to the regular units and don’t cost much more.

Even if your shocks or struts are not leaking, it may be time to replace them. Most suspension movement occurs within a few millimetres of shock travel. The shocks will gradually wear in this range and the change may be difficult to notice over time. They will still work well over big bumps, but handling and vehicle stability decreases during normal driving.

If your vehicle handling feels “soft or mushy” or the vehicle bounces several times over bumps, then it is likely time for new shocks. The change can be remarkable, as the best suspension setups use relatively soft spring rates to cushion the ride and then control suspension movement with high quality shocks and sway bars.

The shocks or struts do not need to be changed to do a wheel alignment, but often a wheel alignment is required after installing new struts because the suspension has to be unbolted. Having the struts changed before an alignment (if required) will save you the cost of a second wheel alignment.

To perform a wheel alignment, the vehicle must be sitting at the proper height. Raising or lowering a vehicle can have a huge effect on vehicle handling because the suspension is working at different angles. The vehicle’s centre of gravity will be changed, and a change in the roll centre of the vehicle (the point around which the vehicle’s body rolls) may cause unsafe handling.

Four-wheel alignment is recommended for most automobiles. The use of independent rear suspension is common in passenger cars and each rear wheel has to be checked with alignment with the front.

The rear wheels play an important part in the way the vehicle steers. If both rear wheels are pointed slightly to one side, the vehicle will travel down the road slightly sideways. You may notice the steering wheel is off-centre as you drive.

If both rear wheels are pointed outwards slightly (called a toe-out condition) the vehicle becomes unstable during cornering. This can become especially dangerous on slippery roads, as the rear wheel with the most traction now wants to control the direction of the back end of the vehicle. Rear wheel toe-out can cause the back end to snap around or spin during cornering or braking on surfaces with poor traction. Drivers may blame poor traction for their spin, when actually the problem may be incorrect wheel alignment and excessive speed.

Good suspensions and alignment are critical for safe vehicle handling. When everything is working correctly, your vehicle will have decreased tire wear, improved fuel economy and a better ride.

james.kerr@sasktel.net