The discussion below on trailer size and weight ratings reminded me of a story.I was at a local show last summer and I was talking with a retired chief engineer from where I work. He collects Fairbanks oil field engines. They weigh in the 2 to 3 ton range. Anyhow he was telling me how he went out to Kansas to pick up his latest engine and loaded it on an appropriately weight rated trailer... i.e 7000 lb. On the trip home, he hit a section of older road on the highway. The road was very slightly wash-boarded. Not enough to notice in a car. But he looks in his rear view mirror and sees the engine oscillating up and down in a natural frequency. Each slight bump in the road makes the engine go higher. He said he went in a mild panic as he slowed down and waited for the engine to stop... This took a while, as there was little natural dampening. He worried all the rest of the way home he had cracked all the welds in the trailer. I told him that was the bane of the engineer. We understand the potential danger/damage we may be in or causing and worry while most people would go on happily. The weight limit on trailers is based on axle rating. The frame and welds probably have not been analyzed, or are of a stress limited design criteria not a deflection limited design criteria. His trailer now has several pounds of extra steel underneath and is way over designed. It is also nice and stable for his heaviest engines.
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