The legal requirement for a tyre is to have at least 1.6mm over three quarters of the width for the full circumference of the tyre - so a worn inner edge doesn't in itself make the tyre illegal unless the tread bracing material is showing through.
If either the inner edge or outer edge wears excessively its an indication the tracking is misaligned (it can be caused by other issues though but tracking is the most common) Tracking error usually also produces a "feathered edge" across the tyre one side of each section of tread - if its feathered on the right of the tyre treads (the right being from the drivers seat looking forwards) then the tyre is towing out too much, if the left edge then its towing In too much - no feathering means track is correct and unusual wear issues could most likely be a pressure issue or other suspension problems.
Its virtually impossible for a pot hole to alter the tracking because the steering track rod would have to bend to change its length -making it shorter and track rods are incredibly robust, likewise, its highly unlikely driving over (straddling) speed humps will create any additional wear to a tyre - solely due to the tiny area the contact patch would be and the randomness of the point on the tyre that additional loading would be, indeed driving one wheel directly over the hump and having the other wheel miss the hump altogether is more likely to break a coil spring due to the sudden load and the amount of travel of the suspension.
The biggest culprit for excessive tyre wear - besides a spirited driver and frequent heavy braking and tracking misalignment are the tyre pressures, If you run overinflated then the centre section of the tyre wears more rapidly as the tyre balloons and creates a smaller contact patch, run underinflated and the centre section squishes in far too easily and both outer edges take the brunt of the wear. Under inflation also cause the sidewalls to excessively flex - generating heat and can create premature failure of a tyre and premature aging (cracking in the tyre wall) tyres regularly run under pressure are easy to assess not only by the tyre wear pattern but when the tyre has been taken off the wheel the excessive heat generated creates a discolourment on the inside of the tyre.
All tyre pressures indicated for a car takes into account a lot of variables specific to that car, its weight, its performance, load variances, its size, and tyre pressures are set when cold - however, when cold the tyre isn't at the right pressure - its based on the heat generating characteristics of that tyre which is determined by its size, load rating and construction, its correct pressure is achieved only when the tyre has warmed to its optimum tyre temperature - which usually takes 10 to 15 miles of driving - dependant on load and driving style and speed.
If you regularly drive just a short distance - like many do travelling to work - just a few miles then its advisable to raise your cold pressures by 2 to 4lbs to take into account the tyres will not get to optimum temperature and therefore optimum pressure (as heat creates expansion and increased pressure), short trips can be identified by looking at the tread wear pattern - the centre section of the tyre will have more tread than the two outer areas - and why when tyre depth is measured they are measured outer, centre and inner. You can establish a lot about a driver and how their car is looked after just by looking at a tyre
If either the inner edge or outer edge wears excessively its an indication the tracking is misaligned (it can be caused by other issues though but tracking is the most common) Tracking error usually also produces a "feathered edge" across the tyre one side of each section of tread - if its feathered on the right of the tyre treads (the right being from the drivers seat looking forwards) then the tyre is towing out too much, if the left edge then its towing In too much - no feathering means track is correct and unusual wear issues could most likely be a pressure issue or other suspension problems.
Its virtually impossible for a pot hole to alter the tracking because the steering track rod would have to bend to change its length -making it shorter and track rods are incredibly robust, likewise, its highly unlikely driving over (straddling) speed humps will create any additional wear to a tyre - solely due to the tiny area the contact patch would be and the randomness of the point on the tyre that additional loading would be, indeed driving one wheel directly over the hump and having the other wheel miss the hump altogether is more likely to break a coil spring due to the sudden load and the amount of travel of the suspension.
The biggest culprit for excessive tyre wear - besides a spirited driver and frequent heavy braking and tracking misalignment are the tyre pressures, If you run overinflated then the centre section of the tyre wears more rapidly as the tyre balloons and creates a smaller contact patch, run underinflated and the centre section squishes in far too easily and both outer edges take the brunt of the wear. Under inflation also cause the sidewalls to excessively flex - generating heat and can create premature failure of a tyre and premature aging (cracking in the tyre wall) tyres regularly run under pressure are easy to assess not only by the tyre wear pattern but when the tyre has been taken off the wheel the excessive heat generated creates a discolourment on the inside of the tyre.
All tyre pressures indicated for a car takes into account a lot of variables specific to that car, its weight, its performance, load variances, its size, and tyre pressures are set when cold - however, when cold the tyre isn't at the right pressure - its based on the heat generating characteristics of that tyre which is determined by its size, load rating and construction, its correct pressure is achieved only when the tyre has warmed to its optimum tyre temperature - which usually takes 10 to 15 miles of driving - dependant on load and driving style and speed.
If you regularly drive just a short distance - like many do travelling to work - just a few miles then its advisable to raise your cold pressures by 2 to 4lbs to take into account the tyres will not get to optimum temperature and therefore optimum pressure (as heat creates expansion and increased pressure), short trips can be identified by looking at the tread wear pattern - the centre section of the tyre will have more tread than the two outer areas - and why when tyre depth is measured they are measured outer, centre and inner. You can establish a lot about a driver and how their car is looked after just by looking at a tyre
