Well put. All these numbers are 'decided upon' by many people, all with differing motivations. It's not 'Engineers know best' cause you don't even know who made the final decision.steve68steve said:Speaking to the maintenance interval itself:
1. Some think the designers/ OEM knows best and everything they do is calculated down to the nth degree.
2. Some think it's all about the bean-counters. Tight maintenance intervals are just a profit center (racket) for the dealerships. ...or maybe that the designers/ OEM just pulls a number out of their butts.
Many years ago, I was a mechanical engineering student. An exam question was - given material properties (strength, weight, yield, etc.) - what diameter must the landing gear struts be to safely complete 100,000 landings before metal fatigue requires replacement.
Point: the fatigue failure of metal is a science. It's known, calculable, and repeatable (altho does not account for manufacturing defects). There's also a long history of industry standards, field experience with similar models, statistics, etc. This makes the case for item 1, above.
Profitability is always a concern. Legal exposure is a consideration, so they are motivated to require keeping the machine well-running to avoid failures which could lead to lawsuits. They also need to keep the dealerships profitable. So, very short maintenance intervals are a no-brainer, right? This speaks to item 2, above. Except that if they're too short, they communicate a possible reliability problem, design flaw, or high cost of ownership to the end customer, which kills sales.
So the reality is that these sides pull on each other until some balance is achieved. If a competitor has maintenance interval X, maybe Marketing wants theirs 1.2X just to look more reliable. Sales want it 2X. If dealerships are complaining about profitability, maybe Accounting wants to make the interval 0.8X to help. If field failures are happening, maybe Engineering want to make it .5X. A decision is reached.
So technically, both biases are probably wrong but the truth really DOES lie somewhere between the extremes of "never" and "always."
And not all engineers are the same. Science even isn't the end all, as 'people' are involved in the equation. I question everything.
“The more you know, the more you know you don’t know.”
— Aristotle