Thor Forums

[TyCreek]

Originally Posted by Chance

As far as I know, these are two different issues as they relate to side loads like cross winds.

When you add positive caster, you also add positive trail. They go together. When the vehicle is traveling straight down the road, this added trail causes the wheels to want to stay pointed straight ahead, which most of us would feel as more stable at speed. I think on this we are in agreement.

However, additional caster trail (distance tire contact patch behind steering axis at road) means that if a force is applied from the driver's side, it will create a couple (a torque trying to steer the tires) that will steer the vehicle in direction that wind is pushing it. Instead of the motorhome fighting the wind trying to push it sidewards, it tries to steer itself in that direction; thereby compounding the problem.

Another reported problem with excessive caster is potential for high speed shimmy. Most of us don't drive that fast, but if we did, we wouldn't want the front end shaking like a bad grocery cart.


When I said it's too bad they don't build motorhomes with handling in mind, I was thinking in terms of keeping them low, wide, proper weight distribution, limited rear overhang, etc. Having to "fix" a bad design with stiffer sway bars or the like just doesn't seem appropriate to me -- they should all drive acceptably from the factory.

Chance... Are you really recommending people don't ask to have their caster increased a couple degrees for their RV?

I know the single sided physics principal or fact you quote ... and to that, in the context of "normal" RVs, what do you think would be too much Caster like where the negative might start to outweigh the benefits in real life? ... The though in my head is somewhere around 6.5 degrees or more, though I've never had occasion to prove it to myself as I've never been able to get above 6 degrees with my RVs.

I know first hand what getting Caster into the +5 degree range does for the E- series chassis dating back into the early 90's. I can tell you that there's seldom a travel around where I live that doesn't involve wind and the difference between 3'ish to 5'ish caster is more stability in every condition I've experianced. Since that's about all that can be achieved with typical sleeves on an E- chassis I doubt anybody here could even get into the category of too much or falling off the negative behavior side of Caster! Maybe that is why some might use the reference more is better or get as much as you can.