Many signs of irregular wear look peculiar and the reasons why they occur are not that obvious, so we'll demonstrate them now.  Some irregular wear is specific to the axle the tyre is fitted to; steer, drive and trailer.  Wear can also be affected by the type of driving a truck does or how well maintained the tyre and truck components such as the suspension and the steering are.

Rib depression or rib punch wear is usually found on rib-type steer axle tread patterns.  If the tyre has the wrong inflation pressure for the load it will affect its contour.  This exaggerates the difference between the radius on the shoulder and the centre.  That makes the shoulder and centre areas rotate at different speeds, meaning this rib is almost dragged along wearing more than the one next to it. 

Heel and toe wear usually happens to tyres on the drive axle.  To wear evenly, twin tyres must rotate at the same speed.  If a new tyre is fitted next to a very worn tyre, or one tyre has significantly lower inflation pressure than the other, each tyre will have a different diameter and rotate at different speeds.  This results in the smaller tyre being dragged along causing stress and deformation on the tread blocks that leads to the heel and toe wear you see here.  

One of the most common types of irregular wear is full shoulder wear.  This extends across the entire shoulder rib to a major tread groove, usually only on one shoulder of the tyre.  This excessive side rubbing is generally caused by the wrong toe conditions on the steer axle.  If the wheels are toe out it can cause wear on the inner shoulder, toe in like this can cause increased outer shoulder wear that looks like feathering.  It can also be caused by misalignment to drive or trailer axles.  This is an exaggeration, but if a trailer axle is even slightly misaligned, it means the tractor unit has to drag it along.  It must then counter steer to stay in a straight line.  This will cause extra wear to steer and drive axle tyres, with the road having a similar effect to this file.  If the drive axle is misaligned, it can cause problems on the steer axle.  The bad news is if one axle is misaligned, it can cause irregular wear on pretty much any other axle and cause fuel economy to deteriorate.  When you're driving along, can you see more of the trailer in one mirror than the other? If so, there's a good chance there's some axle misalignment. 

If there's a locking brake, it can cause flat spots on the tyre. This can cause the tyre to bounce or skip and make the irregular wear even worse. 

Stones trapped in tread grooves can cause a separation between the tread and belt.  This results in localised wear.  Even when the stone is released, the worn spot can continue to grow.  The answer? Make sure you spot stones stuck in tread grooves early.

This mottled effect on trailer tyres is another way of seeing if a tyre has been subjected to high lateral stress and harsh manoeuvres.  Tight turns at low speed are a major cause of wear to rear trailer tyres.  Watch in this manoeuvre how the rear-most tyre turns at a different rate to the other two.  The result is mottling to the tyre.

River wear is wavy, like a meandering river.  It only occurs to rib-type patterns on steering and trailer axles, and it usually only shows itself on vehicles driven long distances on motorways.  River wear doesn't affect performance or the number of miles a tyre can cover.  

This might all sound like bad news, but a simple tyre inspection can pick up on a lot of irregular wear. Then you can take steps to prevent it.  In some cases, even rotating tyres can rectify the problem.