Campin LI wrote:
Ron Gratz wrote:
I don't know of any theory which says the front of the truck should rise when you add pressure to the bags without WD being applied. But, it would be easy to test experimentally. Just measure the following:
1) Front and rear heights for truck only with no pressure in the bags and trailer not hitched.
2) Front and rear heights for truck with trailer hitched and no pressure in bags.
3) Front and rear heights for truck with trailer hitched and pressure in bags.
Me either, I am making an assumption that if you raise the back of the truck 2", because the loading on the truck does not change, the front should theoretically raise by the same 2". My thought process is that the airbags pumped up are moving a horizontal datum (of the truck) up 2" vertically (The rake of the truck must remain the same with air in or out of the airbags). I know on my truck, this did not actually happen, I'm thinking maybe suspension friction? Not sure though. The fact that it didn't rise 2" is what makes me think front end rise measurements have been compromised and therefore cannot be relied upon.
Second thoughts popping into my brain now are that the support of the load is what has changed and height does not really come into play because the front of the truck just rotates over the axle.
I think it's starting to make sense. Sorry for thinking out loud.
******Now I don't think there is any front end rise that's going to take place at all. Using a measurement for front end rise directly over the front axle or at wheel well would solve the issue of measurement inaccuracies due to the change in rake of the truck after air is in the airbags.
If agreed, I think my post above could be simplified quite a bit by combining A) and B) above by taking front end measurements directly above the front axle or at the wheel wells to correct for change in rake (don't use bumper measurements). A) and B) from my post above can be accomplished with a little trial and error by adding or removing air and adjusting the WDH each time to maintain appropriate front end measurements.
Yes, heights should be measure at the wheel well opening -- along a vertical extending from the pavement, past the center of the wheel cover, and up to the fender. The axle serves as the pivot (fulcrum). Measuring directly in line with the axle eliminates any effect of chassis pitch-axis rotation.
You mention coefficients above and give them numbers when you set the scenario. What do they represent? Also, if you don't mind, what does "yaw" mean. I tried to look it up but I still don't get it.
Sorry about that. The "coefficients" are spring coefficients with units of pounds per inch. A coefficient of 500 lb/inch means an added load of 500# will cause the suspension to compress by 1 inch.
"
Yaw" is rotation about a vertical axis.
Ron
