Date: Fri, 13 Mar 2009 18:33:24 -0400
Reply-To: Mike S <mikes@FLATSURFACE.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike S <mikes@FLATSURFACE.COM>
Subject: Re: Tires - Why oh why NOT?
In-Reply-To: <5ebe10a0903131223k1d6bfbabwf75ecd511ec79185@mail.gmail.com >
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At 03:23 PM 3/13/2009, Chris S wrote...
>A 1990 Mercedes 560 SEC weighs about 4000lbs. It rides on 205/60 R15
>tires. The tires are not reinforced.
Incomplete info. What's the load rating of the tire you're talking
about? More importantly, what did M-B spec?
>My answer is that our tiny concrete-filled 14'' donuts need to be
>reinforced because nothing else in that size can handle 4000lbs of van
>and furniture, and the 15'' Mercedes tires and wheels are just fine.
First, neither is "4000 lbs." Both Vanagon and M-B 560 have a GVWR of
over 5000 lbs. So start there. Ignoring F/R imbalance, you need a tire
rated at for at least 1250 lbs.
When you actually consider the individual axles, a Vanagon has a GAWR
(rear) of 2866 lbs. So for rear tires, make that a 1433 lb weight
rating, static. I think the 560 is closer to 2600 GAWR, so that's a
100+ lb lower load rating which the MB needs, right there.
But, in addition to considering just the static weight of the vehicle,
you must consider weight transfer during cornering, when the outside
tires carry significantly more weight.
One difference between a van and a sedan is weight transfer during
cornering. The higher center of gravity and consequently greater weight
transfer is part of the reason passenger tires must be derated when
used for truck duty:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=70
VW spec was 185R14C (6PR) (that C means light truck), or optionally,
185SR14 reinforced. This is the same as bay buses, and there's a good
article here: http://www.ratwell.com/technical/Tires.html
Reinforced tires are only necessary if you're using a passenger car
tire, not needed for a light truck tire, see the comment above on the
difference.
There's a Vanagon oriented article here:
http://www.roadhaus.com/tires/guideline.html
Which happens to point to a list of the tires chose as OE:
http://www.roadhaus.com/tires/VW%20Vanagon%20Original%20Equipment%20Tires%201984%20-%201991.html
All of those tires have a load rating of 97 or higher (1580 lbs). Doing
a search on tirerack.com for 1990 560SEL tires, the lowest load rating
shown is a 92 (1389 lbs). Of that difference of 191 lbs, at least 100
is due to the axle imbalance in the Vanagon (VAWR), and the rest can
reasonably be assumed to be there to accommodate the greater weight
transfer experienced by a van vs. sedan.
