Date:         Thu, 08 May 1997 17:49:24 -0400
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         David Katsuki <katsuki@bbn.com>
Subject:      Re: Clarification on Handling of Vanagons

Mark,

On the short wheelbase - the Westy's have exactly the same wheelbase as the
other Vanagons, so I don't think that is a factor.   The handling
differences I'm noticing are not typical of changes in polar moment of
inertia, but rather of soft springing, low spring rate on the anti-sway
bar, more complient rubber bits in the suspension, etc. (aggrevated by some
more weight up top).

On slip angle - Slip angle is a property of the tire, rather than the
suspension and is determined by the construction of the specific tire
(varies from tire to tire).  It refers to the angle that a tire must be
turned relative to the forward direction of a car in motion before it
starts to develop significant turning force (lateral displacement).
Obviously all tires will develop force after a while unless you are driving
on ice, but the slip angle is important because it governs the timing of
the transition from going straight into a turn.   If the rear tires have a
larger slip angle than the fronts, when you initiate the turn, the rear end
will start LATER than the front, causing a momentary oversteer condition
which goes away when you are firmly into the turn.    If the fronts have a
larger slip angle than the rear, a momentary understeer will result when
you start a turn.    The bad problems occur when you are mostly going
straight ahead, since then you are constantly initiating little turns one
way and the other.   Then the momentary understeer or oversteer causes tyou
to be continuously "hunting" for straight ahead, and it feels just like
something is loose or misaligned in the front end.     I notice this every
time I put snow tires on my van, even though they are the same width and
aspect ratio.    I think you would really notice this with a 60 series tire
on the front and a 70 or 78 on the rear.    I don't know whether it would
be undrivable or not.

Dave


At 10:04 PM 5/7/97 -0500, mark keller wrote:
>..... I feel that the short wheel base, 95 inches might
>contribute to your reporting a  differnt feeling with respect to cornering
>on the Westy chassis vs your Wolfsburg chassis. This short distance from
>the tire to the polar axis, the rear wheels, requires the front tire
>sidwall to be stiffer, more ply or a lower profile, 60 series, than a tire
>on a 10 or 15 inch longer chassis.
>
> Do they make an air shock for the vanagon? Again another article spoke
>about increasing the spring rate on the rear by torqing a ratchet type
>device, but I think it was a pre vanagon article.  Does the vanagon have
>the same type of gizmo?

No - this refers to earlier VWs which use torsion bar springs rather than
coil springs.

>
>In your response  to me you said
>
>"On smaller/stiffer sidewall tires in the front only - this can cause very
>>bad handling.   Reason is that  the slip angles of the front and rear tires
>>will then be different, and this will cause one one end or the other to
>>grip and start lateral force sooner in the initiation of a turn than the
>>other end.
>>This effect is most pronounced when the front end tires have a larger slip
>>angle than the rear (as when I put on snow tires in the winter),  but I've
>>also experienced very vague handling with the reverse condition also.
>>With an extreme mismatch it feels like balancing a broomstick.   The
>>extreme example that is always cited is putting on radials in the front and
>>bias-ply in the rear (makes the car undrivable)."
>
>       I don't completly understand your explantion. I wanted to ask what a
>slip slip angle is? I talked with a mechanic friend who said that it is the
>Attitude of the body on the suspension. Ie one end of the vehicle higher or
>lower than the other.  He offered to get a copy of the information to me so
>I have not seen it yet?
>
 . . .