Date: Mon, 16 Mar 2009 10:21:28 -0400
Reply-To: Mike S <mikes@FLATSURFACE.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike S <mikes@FLATSURFACE.COM>
Subject: Re: Reinforced tires - what about other vans?
In-Reply-To: <aeea9b480903160622u133e4jfad749780cd8a500@mail.gmail.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed
At 09:22 AM 3/16/2009, Tony Collins wrote...
>DO the General tire Atimax RT below do the job? They are XL rated
>tires
>
> *205/70R14
>**Load Index 98* = 1653lbs (750kg) per tire
>*Speed Rating "T"* = 118mph (190kph)
>98T<http://www.tirerack.com/tires/Spec.jsp?make=General&model=Altimax+RT&tirePageLocQty=#>
>XL
Those are fine, because they are load rated at 98. This is all easier
than it seems.
VW considers the Vanagon a light truck. When they originally spec'd
tires, light truck tires were rated by ply ratings (6PR, 8PR, etc.)
and/or letter load ranges (A, B, C, etc.). The spec'd a 185/14 6PR/load
range C.
For passenger car tires, they spec'd a reinforced tire. "Reinforced"
(the term "Extra Load" is also used) in this context only means that
the tire is specified to have a significantly greater load handling
capacity than a standard passenger car tire of the same size.
All of those ratings, PR, letter load range, and "reinforced" (or
"extra load") modify the load rating of _the base tire size_. That is,
a 6PR rated tire of one size might have a different load carrying
ability than a 6PR rated tire of a different size. Those ratings still
appear on tires only for backward compatibility with older
specifications. (i.e. for someone looking for a 185R14C 6PR light truck
tire or a 185R14 reinforced passenger car tire)
The more modern system uses numeric codes to indicate the actual load a
tire can carry, _irregardless of the size_. A 97 (1609 lb) rating can
occur on tires of different sizes. This makes things MUCH simpler,
especially if changing tire sizes. When using this system, the PRx,
reinforced, etc. ratings aren't needed.
Passenger car tires need to be derated 9% when used for a light truck
application (because light trucks have a higher center of gravity, are
expected to be loaded near capacity more often, etc.).
Reference: http://www.tirerack.com/tires/tiretech/tirespecskey.jsp
For use on a Vanagon, a passenger car tire must be load rated 97 (1609
lbs). And that is exactly what VW used when they provided passenger car
tires as original equipment on the Vanagon, toward the end of its life.
When derated by 9%, that 1609 lbs becomes 1464 lbs. That is the closest
match to the GAWR-rear (2866 lbs.), without going under. The next step
down, a 96 (1565 lb.) rating, would derate to 1424 lbs., too low for
the Vanagon's actual weight rating.
If VW were spec'ing tires today, they would say use a light truck tire
of load range 93 (1433 lbs) or greater. That exactly matches the
GAWR-rear (maximum rear axle load) rating of 2866 lbs. Or, use a
passenger car tire of load rating 97 or higher, which when derated
properly, is as close as you can get without going under.