Lots of manufactures like Vauxhall/Opel and Ford seem to test their new models of cars by driving it at top speed for hours on end.

What is the point of this?

Does it stress an engine?

1 Answer 1


I've posted this graphic before, but I think it's pertinent here as well:

enter image description here

This is an image of a graph which Carroll Smith put in his book, Engineer to Win. In the book, one of the sections talks about metal fatigue. In this specific graph, he's talking about how stress affects any given metal part: how much will a part take before it fails. The graph describes that a part only has a finite number of cycles in them before they let go. That number, if the part is treated nicely, may be 10,000,000 (or some other stratospheric number). When you put more stress on the part, the parts lifetime is decreased. The effect of the stress is accumulative: the part will not heal itself. As you put the higher stress on any given part, its overall lifetime is diminished. The more stress you put on the part, the sooner it will fail. This is even if you keep it within its engineered limits.

I believe the manufacturer's main reason for testing the engine at the higher stress levels is to try to get it to fail. In doing the testing this way, if it doesn't fail, they know they've done the engineering well. They know the customer will never stress a car this way. If nothing fails in testing, they can be pretty sure the car won't fail when on the road under normal use.

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    It was also the original motivation behind such iconic endurance races as Le Mans; while many forms of racing emphasize speed, endurance racing emphasizes reliability. "To finish first, first you must finish."
    – Edward
    Jan 17, 2016 at 22:03
  • @Edward - Nicely put and concur. Jan 17, 2016 at 22:10
  • I was always told you should stress your engine occasionally, to allow the connecting rods to stretch a bit to prevent a wear ridge on the cylinder wall. If you never stress it, the ridge may form over time, and in the event you then need to take 'er to max revs you could suffer ring/piston damage. Jan 17, 2016 at 22:40
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    Jimmy - depends what you mean by stress. Healthy stress can be giving some WOT regularly, or a good bit of motorway driving for a while to let the engine and exhaust system run at temperature. It doesn't mean hammering it off the rev limiter all the time, for example. And stretching connecting rods? I don't think that's how you avoid wear ridges...
    – Rory Alsop
    Jan 17, 2016 at 23:05
  • Why is the number of cycles the independent variable on this graph? I would've thought they would choose a stress level (the independent variable) then repeatedly apply that much stress until the object fails, and count the number of cycles until that happens (the dependent variable). Jan 17, 2016 at 23:15

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