As an instructor of geometry and theory it’s important for everybody to understand student, or public, there are an overwhelming number of variables and possibilities that need to be recognised with every car, in an ideal geometry there will be no wear in the elastic components of the car, and everybody drives to exactly the same limitation of the text book foundation that the cars geometry was based upon, this obviously is not the case, wear in bushes and suspension occur as soon as the car was driven, so there must be an element of give and take with the maintenance and expectable wear and tear.
Measuring the cars geometry or tracking occur in a static state (not in motion) all settings for the car are based on the idyllic condition, there are small tolerances that allow for the range that the suspension will travel, the reason for this is that as the suspension loads an unloads the wheels geometry will change, this range does not allow for excessively worn suspension, so then it can be said that worn suspension will make any dynamic (in motion) tolerances redundant.
All the best known car rescue services recognise mileage alone as reason to replace suspension parts, as a general rule about 30 to 40 thousand miles, the deterioration of suspension is so slow and, there are very few clues to recognise, so some times you do need to spend money to save money.
Unfortunately there have been some national companies who have made it their business to over sell in this important area and this has made the general public more than cautious in welcoming true advice.
Today most sales are considered as trauma, where the evidence is so overwhelming it’s not in dispute, you must allow for true sound advice as the suspension is in a marriage with the geometry and cannot be denied,
The truth is shock absorbers do not do what they describe, in fact they are shock, after shock absorbers?, as the wheel hits a bump the coil spring loads and preserves the impact, this stored energy will be recoiled but must be controlled, this is done by the shock absorber, the stored energy is recoiled and converted into heat so in fact 2/3 of the suspensions active range is the coil spring not the shock absorber.
Wheels-inmotion has surveyed within the suspension manufacturing industry for a global reference table for ride height, since any true attempted in geometry / alignment must begin with this guide, none of them were able provide one that is commercially available, the best I found was an A4 typed reference, (this I can make available on request by Email)