By where you rock the wheel. Front-and-rear edges reveals steering play; top-and-bottom reveals suspension play.

With the wheel off the ground, gripping it at the three and nine o'clock positions and pushing alternately tests the steering linkage - the tie rod ends and the rack.

Gripping at twelve and six o'clock tests the suspension - ball joints and the wheel bearing.

Have someone watch the joint itself while the wheel is rocked, because movement at the rim can come from several places and only the joint shows where it originates.

Play that appears with the steering locked but not unlocked points at the rack rather than the joints.

A wheel bearing gives movement in both directions plus a rumble, which is how it is separated from the joints.

Yes - they sit under the rack gaiter, so checking them means pulling the gaiter back rather than just rocking the wheel.

The inner or axial joint connects the track rod to the rack and takes the same loads as the outer one.

Because it is enclosed, it is invisible on a normal inspection and is frequently assumed to be fine.

A worn inner joint gives the same wandering and vague steering as a worn outer, so the outer is replaced and the symptom remains.

Checking it means loosening the gaiter clip and feeling for play while an assistant rocks the wheel, or gripping the track rod directly.

A torn or displaced gaiter is itself a finding, because a rack that has lost its gaiter will have taken in water and grit.

Feathering - a sawtooth edge across the tread blocks - because the tyre is being dragged slightly sideways as it rolls.

Incorrect toe makes the tyre travel at a small angle to its direction of motion for every metre the vehicle covers.

That scrubs one side of each tread block, producing an edge that feels smooth in one direction and sharp in the other.

It is distinct from camber wear, which wears one shoulder of the tyre evenly rather than feathering the blocks.

The wear rate is high, so a set of tyres can be ruined between services by a joint that costs very little.

This is why running a hand across the tread at every inspection is worth the ten seconds - the feathering is felt long before it is seen.

Yes - the outer joint is the toe adjuster, so removing it changes the setting by definition.

The outer end screws onto the threaded track rod, and its position along that thread is what sets toe.

Counting turns on removal and matching them on the new part gets the vehicle to the alignment bay safely; it is not a substitute for measuring.

The new joint's centre may sit at a slightly different length than the old one even at the same thread position.

The old setting was also compensating for the wear that has just been removed, so it was not correct to begin with.

Set the steering wheel straight before adjusting, or the vehicle will track correctly with an off-centre wheel - which is a common complaint after this job.

It locks the outer joint at the toe setting. It must be properly torqued after alignment, and it is what stops the setting drifting.

The joint screws onto the track rod thread, and nothing but the locknut prevents it unscrewing under vibration.

A loose locknut lets the toe change progressively in service, so the vehicle leaves the alignment bay correct and is wrong a few weeks later.

It must be tightened after the alignment is set, not before, and the joint held against rotating while it is done.

Torque it to specification - overtightening can damage the thread or the joint housing.

Check the locknut is tight as part of the alignment sign-off. It is a common omission and the resulting complaint is hard to diagnose later.

Usually, because both have done identical work - and where the labour overlaps, doing one alone means paying for the alignment twice.

Tie rod ends on the same axle experience the same loads and the same environment.

When one has worn to the point of replacement, the other is typically close behind.

Since the job requires an alignment either way, replacing the second joint a few months later means a second alignment as well.

The exception is genuine single-side damage - a kerb strike or a boot torn by debris.

Check the inner joints and the rack gaiters at the same time, since the corner is already accessible.

It is the link between the steering box and the steering arm on vehicles with a recirculating-ball box rather than a rack - common on heavy vehicles and off-road designs.

A rack-and-pinion system pushes track rods directly from the rack.

A steering box system uses a pitman arm, a drag link and often a relay or idler arm to get the movement to the wheels.

That gives more joints, and therefore more places for play to accumulate - a small amount at each joint adds up to noticeable steering slack.

Idler arms and relay rods are wear items in their own right and are checked the same way as tie rod ends.

Many of these joints on heavy vehicles are greasable, so they belong on the lubrication schedule rather than only on the inspection list.