Originally Posted by ald2120
I was under my 2001 class b coach and plulled down hard Rear frame. the front end bounced a lot,which seemed strange to me, like bad shocks. I then increased my rear air shocks to around 70 lbs. Once I did that putting my weight on the Rear bumper caused no bounce . I travelled 800 miles one way,on my first trip since getting it with 116,000 miles and it drove nice. In side winds you can get a little side to side because of the wind. On a calm day 70 mph is top speed for me. Have someone bounce the rear bumper and look under to see what the front end is doing. This is my opinion only.
new front tires also helped. Still running old rear for now.
That is a pretty interesting occurrence. I would normally expect the having the back firmer to make the front bounce a bit more in a porpoising type movement, pivoting around the rear. That is what usually happens when you put in softer springs in the front or less dampening shocks. The back must just be so soft that the whole van moves down so much the front gets brought along. Did the back keep bouncing like the front?
What isn't surprising is that going with more air in the bags improved handling and sway. If the spring rate on an end (rear in this case) is increased, you reduce it's traction some, and increase the traction on the other end (front in this case). Increasing front traction reduces understeer and makes the steering much more responsive and easier to control. Of course, the stiffer rear springing also reduces the physical rocking of the van from side blasts of wind or from road ruts, and that rocking can sometimes be enough to make both the front and rear "self steer".
One thing that I think is the important in all of the handling in wind stuff is realize that you aren't really going to be able to get the van to not move sideways when hit by a big gust of wind. At least we have never seen it in any of our vehicles over the years. What you do want to happen is that front and rear react the same way when that gust hits. If the front and back both move the same amount, the van is still going straight, just moved over a little, so all you need is a small correction to get back where you were with no real direction change. If the front moves more than the rear, which I think is common in vehicles that understeer like our vans, you l are also left with the van actually pointing in the way the wind pushed it. It will get further off line from that change in direction the longer the time is until corrected, and it will take a larger amount of steering movement to correct both the direction and bigger amount you have moved. Added on top of that is that if you have understeer, the steering input has less effect and thus needs more movement. This all leads to big steering wheel inputs and easy to get overcorrections, which can make the vehicle quite hard to drive.
IMO, a good test of handling neutrality and stability is to actually get a measurement of how big the steering wheel corrections have to be under varying conditions from calm to very gusty and windy. I think a very well behaved van can be under 1/2" of movement in good conditions, and well under 1" in the wind. We routinely see people sawing on steering wheel in windy weather with steering inputs that look to be approaching 3", which has to be really tough to do. We saw a Dodge Roatrek 190 that was all over the road, and he was correcting probably 45* on the wheel at every oscillation.
In some of the other handling theads here, there have been lists posted that show what changing things like springs, shocks, sway bars, tires and pressures, etc do to handling, some of which is contrary to what logic would indicate.