Effects of suspension and steering on tyres
As we head into the final days of Tyre Safety Month, it is easy to think that checking tyre pressures and tread depths are the only technical inspections that need be carried out on a regular basis. As important as they might be, try not to overlook other aspects of the car, which are critical to ensure that the tyres can work to the best of their abilities.
While the term ‘dampers’ is more appropriate, one of their functions is to ensure that the tyres maintain contact, after negotiating bumps in the road surface. Worn items result in insufficient damping, which prevents consistent tyre interaction with the tarmac. While leaking dampers are obvious MoT failures, items that have started to ‘mist’ may be only an advisory item. The pictured ‘misting’ damper, for example, passed the MoT Test less than a week before being replaced at a subsequent service. Some garages can test the dampers’ performance rates more accurately than a simple DIY bounce test, by using a vibrating plate, and they can advise you on the degree of wear. Never try to cut costs by replacing dampers singularly, because this can introduce an imbalance between the new and worn parts – always replace dampers in axle pairs. The same also applies with suspension springs that, on some models, can break and pierce the tyre sidewalls – always replace them in axle sets.
Over time, rubber bushes perish and wear, factors that introduce excessive movement in the various steering and suspension components. While excessive play is an MoT failure point, bushes that a tester may consider as acceptable could have softened over time to introduce unpleasant handling characteristics that can make the car react differently to what its maker intended in a high-speed emergency manoeuvre, thus increasing the risk of the tyres losing grip. Although upgrading to ‘harder’ bushes helps to reduce movement (which may not be desirable in some situations, such as when bush movement is intended to aid handling), they tend to transfer more road noise to the cabin and decrease the ride quality. All your car might need is new bushes of the standard specification.
A driver’s steering wheel input must be reproduced faithfully via the steering mechanism to the tyres at all times. While major problems, such as excessive movement in the steering joints and power steering fluid leaks, will fail the MoT Test, a number of issues can affect the steering responses negatively but may not necessarily declare the car as formally unroadworthy. These may include a weak, or failing, hydraulic power steering pump, minor wear in the steering column, rack and their mountings, or incorrect wheel alignment.
The latter point (known otherwise as ‘tracking’) not only influences vehicle steering, handling and tyre grip but it also causes rapid and uneven tyre wear, in the majority of cases. Factory-set wheel-alignment deviates naturally from its specification as the various components age and wear but the rate at which it does so is accelerated by exposing the road wheels to sudden impacts, such as those experienced when driving into a pothole, or over a raised kerb stone. Therefore, regular wheel alignment checks are advisable. Most cars’ front wheels can be adjusted only, which tends to be inexpensive. Yet, if your vehicle possesses either rear-, or all-wheel-drive transmissions, the rear suspension may also possess adjustment points, and the procedure can become more involved and costly.
If you are considering replacing your tyres, consider our findings on why premium tyres are worth the extra investment. Also, bear in mind that an MoT Test pass does not guarantee that your car will remain safe and roadworthy another full year. Treat any advisory notices from the tester as mandatory and having your car serviced regularly will increase the likelihood of worn components being replaced, before they become dangerous.