At 03:26 PM 8/22/2012, neil n wrote: >Are you suggesting one ramp per vehicle corner, Yes. > each providing room and level surface for a jack and jack stand? Stand or wheel for sure. Another for the jack would be a good idea as well. > > >Like this? image: >https://lh3.googleusercontent.com/-zCqGzE1KbmI/UDUyJPKF0WI/AAAAAAAAF_U/cBj1mBmkZ-Q/s800/ramp.jpg Yes, exactly.
>For what I need, 2 ramps should suffice for now. (work on one end of >vehicle at a time) Safer to have all four, though if the other end is chocked very securely perhaps it would be all right. But by getting all four support points (wheels or jack stands) on a level surface, you've eliminated any forces tending to topple the stands or otherwise move the vehicle horizontally, and you've ensured that the center of load on the stand runs right down through the middle and not off to one side where it would require less force to topple it from the other side. The jack has all the same considerations except that you're not underneath at the time, so if it's practical to level it it's a very good idea, and you have to stay conscious all the time of how the force vector decomposes at a given angle. If your driveway has a constant slope you can easily make up two tables: for a given load, how many pounds of force are exerted horizontally; and for a given height of lift, how far does the load center move horizontally from the midpoint of the (tilted) lifting/supporting device. Example: 4000# Westy sitting on a 3* slope. Force vector is 4000# straight down, but the slope decomposes that into approximately 3995# pressing against the driveway, and 210# trying to make it run off down the hill. And a jack or stand sitting on the slope would have the effective center of load an inch to the side of center. Six degrees would give you 420# shoving you down the hill, and the center of load two inches off the centerline of the stand. Doesn't sound like all that much, but every little bit hurts. Yours, David |
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