Date: Fri, 2 May 1997 22:59:23 -0400
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: kelphoto@mail.bright.net (mark keller)
Subject: Part 2 Handling differences between 87' Camper/Van
> Part 1 Well, I read the note about handling and swaybars etc for the new
>camper owner. A couple of things occured to me that can shed some light on
>the differencs. I'm kinda rusty on this, its from my aviation days, but
>here goes.
>
> Motor vehicles have a few things which affect the cornering or
>broadly speaking handling on the road. Where to start? Well polar axis is
>where the van actually pivots when cornering, around the rear wheels, kinda
>like a shopping cart.
>
> Center of gravity is both a horiztal and vertical location, kinda
>of an x axis, y axis thing. Imagine if you were to " horizontally spin" a
>van around its Center of gravity. I submit that a van's spin axis would be
>closer to the polar axis, since compared to a camper the weight distrubtion
>is more to rear. The spin axis of camper would be much farther foward of
>the polar axis since nearly all of the added weight is forward of the polar
>axis.
>
> Using a shopping cart for example, the more weight you add to the
>nose of it, milk,meat,canned pop, and etc, the harder you have to work to
>turn the thing. Contrawise if you were to place these items in the back, on
>top to the polar axis you could "turn the same weight" with much less
>effort. Ok now to the tires.
>
> Since it's the front tires that must generarte the force, to turn
>the van, sidewall construction, and centrical force interplay to do the
>job. Micheliens, as rule have the most flexiable sidewalls of all tire
>brands, that's why I love em. They ride great!! However a cost is
>involved, at slower speeds the sidewalls aren't that ridged and the
>"handling is kinda mushy. But, cleverly, Michelien's have most of their
>weight at the outer circumferance in the tread and hence are able to
>generate great centrifical force at high speeds, which in turn makes the
>tire very rigid , but absorb bumps and stuff very well.
>
> There's more to say about the height change in the vertical
>location the Cg between the two vehicles but I've got to get back to the
>salt mine, more later. MK
>
>PS email me any questions in the meantime I'll try to clarify or own up to
>my mistakes.
Part 2
The center of gravity's height above the vehicle tire's center is
the next thing to consider. As the van becomes more top heavy the greater
the leverage this weight has on the pivot point, the suspension. So if the
camper Center of gravity is higher, than a van, and it may not as I'll
discuss later, when you turn more force is applied to the suspension and
you bus turns like a sailboat. You can beef up your swaybar, assuming
there is a supplier. Or increase the spring rating. I don't know what
possiblities you have for this. Now for the CG flip side.
On a camper some of the weight is added beneath the floor or right
at it. Propane, and water tanks and etc. This offsets the weight added in
the roof. So the CG probably is not as much a factor as the increasee
weight and forward CG
Some possible things to consider weight and balance wise.
1. Consider moving anything you can from the front of the
camper to the rear such as. Spare Tire, batteries, I dont' know if the rear
fuel tank location like a Syncro is an option, but that would also be a
consideration. Any or all of these items would move your center of gravity
rearward and have benefical effect on the force required to pivot the
vehicle.
2. Tire tuning. Lower profile tires provide greater corner
force, since there is less sidewall to flex, and they're side walls are
generally thicker too. Light truck tires and RV tires, have more sidewall
plys, your choice 4, 6, or 8 plys for all of the above mentioned problems.
Since it is the sidewall which is responsible for generating the force in
turning.
A Light truck/ RV tire with 4 6 or 8 sidwall plys would be a
possible path. The tire height would be the same as your current tire. see
below.
If ground clearance is not a concern a low profile tire could lower
the vehicle as much as an inch. At highway speeds more air is forced around
the vehicle instead of under it resulting in a lower required road
horsepower for every given speed.
For example the Syncro's nose is at higher attitude and also the
vehicle sits overall an inch or inch and half higher. I read that the road
horsepower to push a Syncro was somewhere in the 33 hp at 50 mph, and 65 hp
at 70 mph. I don't know the values for a Vanagon, but a late model
passenger car, road horseposer is in the 20hp at 65mph range. Lowering the
vehicle fractions of an inch can really help. A short tire on the rear
though would in effect increase the rpms per mile, but increase the lower
end acceleration. Supposing you went with the 1" shorter tire on the rear,
expect 5% increase in Rpm. So if you cruise now at 65mph and 4400 Rpm, 65
mph would be 4620 Rpm.
If your running the 205/70 14, the your tire height with new tread is
around 25.25". A 225/50 14 would be 23.9" tall. Just over one inch
shorter. This tire would have the potential to generater lots more
cornering force.
I would consider trying a set of lower profile tires on the front
only. That way you don't mess with the rpm thing or your speedometer
accuracy for that matter. Light Truck/RV tire would have no benefit for
lowering your road horsepower, but would increase your cornering force.
Since the vanagon chassis has a relativly short wheel base, 95"
compared to 115" of other vans, the front tires have less leverage and must
produce more force, than longer wheel base vehicles which the tires are
designed to work on.. The simplest thing to address is the two front tires.
Lower profile, or RV or light ruck tires with more sidewall plys. In terms
of moving things around someone with more Camper experience maybe can
suggest real solutions. The swaybar fix will transition the weight to the
tires quicker;but the tires still must generate the cornering force. I hope
this helps. MK 91 Carat.
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