Date: Sat, 14 Mar 2009 16:53:51 -0400
Reply-To: pdooley <psdooley@VERIZON.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: pdooley <psdooley@VERIZON.NET>
Subject: Re: Tires - Why oh why NOT?
In-Reply-To: <B979EFADAABF4DE6BEF7B2DCE98AD335@mike2d93581d7f>
Content-type: text/plain; charset=us-ascii
I seem to remember the old bay window buses handle the snow and ice better
due to more weight on the rear as compared to the Vanagon. Add that to
other list members saying the Vanagon is balanced if not heavier on the
front axles, and I made that assumption.
So, has anybody actually weighed a Vanagon with typical fuel and passenger
load and determined the weight per axle in a real world situation?
Regarding the polar moment of inertia, I didn't bother to bring up the axes
of orientation since the terminology is incorrect in the first place.
For your argument I think the term "center of mass" fits better, since we
are still talking about weight distribution and not rigidity.
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Mike
Sent: Saturday, March 14, 2009 3:18 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Tires - Why oh why NOT?
No, it hasn't been shot down, it's been backed up by factory specs.
Regarding the 'polar moment of inertia' , you're only considering rotation
about a single axis, and that's not the axis that I'm referring to here.
There are 3 axis' affecting a moving vehicle; lateral (pitch),
longitudinal (roll or 'torsion') and vertical (yaw).
I'm referring to rotation about the vertical axis, induced by weight
biased more towards on end than the other. Like a pendulum, it's the same
force induced that's been pulling VW Beetles and Porsches off the road
backwards since they first made them.
Our Vanagon suffers the same effect, but not so extremely, as the
rear-weight bias
is not as severe as in those other examples. These vans are heavier
overall, and are also capable of carrying both heavier payloads as well as
the number of passengers. They are, therefore, designed and engineered
accordingly.
They are, in fact, a light truck capable of hauling alot of additional
weight, and do so regularly on the Camper and Syncro/camper versions.
In addition, towing anything would only add to this rear-weight bias and
result in a more pronounced over-steer in a panic situation.
As you can see, the tires need to be very stout in the sidewalls to handle
all of the extremes that the vehicle may be subject to, including during
mishaps like emergency braking and evasive maneuvers, or in the event of a
tire blowing out. TUV standards in Germany set most of these requirements
that follow the vehicle wherever its sold.
I'm sorry, but any passenger tires are woefully inadequate for any Vanagon
(including an empty passenger van with only the driver), and will result in
poor handling and dangerous uncontrollability in a panic situation.
How much value do you put on your family?
Mike B.
----- Original Message -----
From: pdooley
To: vanagon@GERRY.VANAGON.COM
Sent: Saturday, March 14, 2009 2:32 PM
Subject: Re: Tires - Why oh why NOT?
Mike,
Apparently the weight bias issue has been shot down already, so please
explain the polar moment of inertia part.
It's been a long time since my engineering classes, so I looked it up.
From what I found, the polar moment of inertia is a measure of an object's
ability to resist torsion.
You seem to be implying that a weight imbalance will affect the vehicle's
torsional stiffness.
Please clarify.
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Mike
Sent: Saturday, March 14, 2009 10:48 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Tires - Why oh why NOT?
The imbalance by the rear-biased weight, and a resultant high polar
moment
of inertia during evasive maneuvers (or during a tire blow-out), is surely
the main reason for the C-load sidewall requirements, as evidenced by the
tire pressure requirements (high overall and even higher in the rear).
No passenger tire is rated or able to withstand those high pressure
settings. If you inflate a passenger tire to 44 - 48 psi, it will make it
form a different shape, causing the tread to lose total contact with the
pavement, as well as unduly stressing the carcass and ultimately causing
tread seperation and sudden and possibly catastrophic failure. All this
will likely occur at the worst possible moment, like when you've got 8
people in the van and going 75mph down the highway.
If you've never experienced a high-speed tread separation, I can tell
you
it's the most out-of-control feeling you'll ever experience. Rear tire
incidents are much worse than on a front tire, due to being able to move
the
steering wheel to fight a front tire blow-out. A rear tire blow-out
controls you, not vise-versa!
Also, any tire retailer that sells and/or installs the wrong tire for
your
vehicle, can be held liable in court for the damages/ injuries/ deaths
caused by it.
To take it one step further, if your state inspection sticker passes
with
the wrong tire(s) installed, they too could be held liable for not
rejecting
it as a failure.
Mike B.
----- Original Message -----
From: Mike S
To: vanagon@GERRY.VANAGON.COM
Sent: Saturday, March 14, 2009 10:00 AM
Subject: Re: Tires - Why oh why NOT?
At 08:58 AM 3/14/2009, Chris S wrote...
>Now, let's compare some more.
>
>I once had a 1993 Ford Aerostar. Its curb weight was 3400 lbs and it
>could carry 7 passengers. No where did the manufacturer specify
>reinforced tires. The stock 215/70 R14 tires, which fit the Vanagon,
>have a max load rating of 1554 lbs. The tires are NOT reinforced.
That's not a standard load rating:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35
Would that be the 1993 Aerostar talked about here?
http://www.allworldauto.com/comments/1993_ford_aerostar_comments_and_complai
nts_24771.html
Where the following comments have been made:
"Tire blew out on interstate, entire side. was driving at normal speed
in normal conditions."
"Tire blew out, when vehicle stopped tread was seperated from rest of
tire."
"my front left tire suddenly blew out."
"the left rear tire suddenly went flat"
"failed with a tread separation blowout"
"tread coming off tire"
>A 1991 Vanagon GL has its curb weight listed at 3400 lbs. But somehow
>its tires are required to be reinforced.
You're not convincing anyone that you know more than the factory
engineers. Why would you presume to apply Ford specifications to a VW?
It would just as valid (that is, completely invalid, although quite
obviously safer) to go the other way. As has been pointed out, VW never
equipped the Vanagon with tires having a capacity of less than 1609
lbs. (load rating 97), although they could have saved money by doing
so.
Hey, I've got a set of el-cheapo 185R14 passenger car tires, with rims,
which the PO had on. Want to buy them cheap?
