I used to work for a heavy truck manufacturer in their test facility. I would help certify things like fuel tanks, safety belts and brakes as well as less obvious safety items like winshield wipers. I didn't see much built in margin on a lot of these items. Now a 30g static pull test on seat belts for 30 seconds is pretty rigorous, but federal fuel tank test requirements were a joke in my opinion. When you have to test anything through 2 redesigns to get it to pass a federal requirement, you can bet there isn't a huge margin in the third design. By then, the loads and failure mode are more clearly defined, and the development budget is used up, so the presure is on to get a design that passes the letter of the law without breaking the bank.
Now these are heavy trucks, with "professional" drivers, in that they have more training than is required for a passenger car, so that may be an argument for less margin. Just two cents from a guy who used to run the hydraulic cylinders and the data acquisition... Seth
