Originally Posted by OKI Marine
I to am an engineer and worked many years in the tool & die industry. I get your point and have looked at my tires in the mirror while making a tight sharp turn in our court in front of our home at nearly no speed at all. One tire flexes inward while the other flexes outwards. It is not a pretty sight and have often thought that there has got to be some damage done there. Maybe you could calculate a chart with given speeds and angularity of turns and share here on the forum for others to apply. Do you have any test data?
Test data? I wish! It would be fun to generate some test data, but this requires time and instrumentation that I don't have. I'd need a way to measure the forces on the outside tires. I'll have to leave this for the big guys.
What I've done is math and physics, and concluded that there is a likely problem here. (It's hard to be wrong about this if the tires are loaded to the max when the trailer is sitting still)
I have a spreadsheet that shows my calculations and am happy to share if we can figure out how to do that. PM me if interested.
I needed a reasonable benchmark for speeds on curves. What I found is that the advisory speeds are well defined in a way that makes calculating lateral g-forces easy. Advisory speeds are also reasonable speeds to drive comfortably when towing, based on my experience. They're based on readings on a Ball Bank Indicator. Speeds on advisory limit signs are set according to the following table that's in the MUTCD:
35 mph max bank angle 12 degrees
25-30 mph max bank angle 14 degrees
20 mph max bank angle 16 degrees
The Tangent of the bank angle gives the lateral acceleration on the trailer in g's.
Multiply that times the weight of the trailer and you've got the lateral force on the trailer.
Multiply the lateral force on the trailer by the height of the center of mass of the trailer and you have the torque that's working to tip the trailer towards the outside of the curve. Units are ft-lbs in my spreadsheet. I guessed my center of mass is about 4ft off the ground. The first two feet of this is air under the trailer.
Divide the torque by the side to side span between wheels and you have the restoring force on the outside wheels that keeps the trailer from tipping over.
Divide by the number of axles, and you have the added force per tire.