Date:         Sat, 29 Oct 2005 13:12:45 -0400
Reply-To:     The Bus Depot <vanagon@BUSDEPOT.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         The Bus Depot <vanagon@BUSDEPOT.COM>
Subject:      Re: Oh Boy! Tire Thread! (was RE: Michelin LTX/MS 215/75R15
              tires...)
In-Reply-To:  <6da579340510271230g693fe4aay134c5bdc8a43524c@mail.gmail.com>
Content-Type: text/plain; charset="us-ascii"

>  But if you're on 16x7.5 rims, for which your
> "silver sticker" has no tire recommendation, what 
> specs do you use? The ratings are obviously 
> going to be conservative, but there's no real way 
> to know HOW conservative. Lucas at GoWesty is
> confident that the HydroEdge tires he sells are 
> well within the "engineering hedge"


But we DO know what specs to use if the tire is other than the silver
sticker size, thanks to Larry's research.  We do not have to guess.

We know that the the GAWR (gross axle weight rating) on the Vanagon is 2866
lbs, or 1433 lbs per tire (a bit more for a Syncro). We also know that U.S.
D.O.T. safety requirements call for the tire to have a 6% safety margin
above this if it is an LT rated tire. If it is a passenger car tire is must
first be de-rated by 9.09% (load capacity divided by 1.1) and then the 6%
margin applied to the resulting value. All this is as per government safety
guidelines, and is irrespective of tire size. If you do the math, this means
that an LT rated tire must have a load capacity of 1520 lbs, or a passenger
car (P-rated) tire must be rated at 1670 lbs, to be considered by the D.O.T.
to be safe to use on your Vanagon.  (VW, who of course knows the most about
their own vehicles, goes even further. On late model Eurovans, which have
16" tires and a similar GAWR to a Vanagon,  they recommend a 100 load index,
which is 1764 lbs.)  

Therefore, a 1510 lb capacity passenger car tire such as the one on the
GoWesty site is substantially below all published safety guidelines for the
Vanagon. Of course Lucas feels that it is safe anyway. So it comes down to
choosing whether to follow Lucas's opinion or the more stringent U.S.
government and VW safety guidelines.  Given that tires are available that DO
meet the published safety standards, I personally can't see any logic in
taking chances with a tire that doesn't.  But then I'm pretty cautious when
it comes to safety and am also the type to never drive without my seatbelt.
Others may make different personal decisions. 

- Ron Salmon
  The Bus Depot, Inc.
  www.busdepot.com
  (215)  234-VWVW

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