Date:         Fri, 18 Mar 2005 19:01:56 +0000
Reply-To:     Mike Finkbiner <mike_l_f@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Mike Finkbiner <mike_l_f@HOTMAIL.COM>
Subject:      Re: Another Stupid Tire Thread..was Re: 15" Wheel/Tire Report -
In-Reply-To:  <MC10-F39j6iZkxUWZoI0005183f@mc10-f39.hotmail.com>
Content-Type: text/plain; format=flowed

>From: Phil Zimmerman <phil.zimmerman@MAIL.CRCN.NET>
>To: VANAGON@GERRY.VANAGON.COM,              Finkbiner Mike
><mike_l_f@HOTMAIL.COM>
>Subject: Re: Another Stupid Tire Thread..was Re: 15" Wheel/Tire Report -
>Date: Fri, 18 Mar 2005 11:18:40 -0500

>
>On Thu, 17 Mar 2005 05:30:21 +0000, Mike Finkbiner <mike_l_f@HOTMAIL.COM>
>wrote:
>
> >My '87 Westy says 185R 14 C (which only means Commercial rated) at 48 psi
>on
> >the rear OR 215/70R14 LR 97 at 40 psi on the rear (based on my best
> >recollection).  They don't specify a load rating for the 185 because one
> >which is built to handle 50 psi is load range 93, so 48 psi is almost max
> >pressure.
> >
> >Tires can handle the rated load only at maximum inflation pressure, and
>LR
> >93 will carry a Westy, at full pressure.  Drop the pressure, drop the
>load
> >handling capacity.  The 215s at 40 psi would be at 80% pressure, which
>means
> >you couldn't expect them to handle the full load, so they specified LR
>97.
>
> >- Mike
> >
> >Mike Finkbiner
> >'87 Westy (wearing Haaka CQs in 185R14)
> >Moscow, Idaho
> >mike_l_f@hotmail.com
>
>Hi Mike,
>
>Thanks for the informative post on: "another stupid tire thread".
>Your insights filled in a few voids that have persisted in my understanding
>of tires for a Westy.
>
>The word "reinforced" especially. I still remain a bit puzzled as to why
>the silver door sticker
>designates "reinforcement" for the 205:70R X14 tire option. I follow your
>description (and
>surmised  this myself) as to why the 185X14 "C" didn't need to be
>reinforced.... It already was....
>so to speak!
>
>A 205:70R X 14 load rated 97 tire at maximum inflation pressure still needs
>to have a
>"reinforcement" designation but, only if one were to run it at "lower than
>maximum inflation
>pressures".  Is my understanding here correct or still muddled ?
>
>Phil Z.
>'87 Westy
>Campbell River, BC


Phil -

As I see it there are three factors to consider in load capacity: Max
capacity, max pressure and intended pressure.

  (There are lots of other factors like size, tread design, company
reputation, etc. that are important, but not for load)

If you have a tire with Load Rating 93, max pressure  50 psi, it is designed
to carry 1433 lbs at that pressure. A couple of pounds less won't matter,
but if you drop it to 40 psi, it will.  How much less?  Hard to say.  Truck
tires have a load/pressure chart and I imagine the manufacturer could supply
you with one for light truck and passenger tires, but they aren't common.

Take the same tire with a load rating of 97 and it is designed to handle
1609 pounds at max pressure.  If that's 50 and you take it down to 40 I
imagine it's good for 14-1500 at that pressure, so I can see why VW
specified that rating, but I'm sure it varies based on the tire's
construction.  If the max pressure was 60, I would be more cautious, because
40 psi could be too low to handle 1400 lbs.

Based on my understanding of "Reinforcement"  a  205/70R X 14 load rated 97
tire which has a max pressure of more than 35 psi is reinforced.   If the
max pressure is 44, you should be able to reduce it to 40 and still have
plenty of reserve.

However, if the load rating were 93,  you would need to leave it pretty
close to 44 to be able to handle the weight of a Westy (IIRC my rear axle
spec is almost 2800 lbs.  If I were smart I would go look at the data plate,
but it's not here.   The front axle has a lower max load, so you can run LR
93 tires at the  lower pressures they recommend and not be overloading them)

This whole discussion ignores the handling aspect.  Raising and lowering
tire pressures changes their stiffness and will make a big difference in the
way the van handles.  On my '87 Westy, if I drop the pressure on the rear
tires to match the fronts, everything starts feeling squirrily.  Higher load
ratings and higher max pressures allow you to make more adjustments.   Of
course if people report that they are happy with a particular tire, and it
will handle the load at the pressures they are running, that should make you
  more confidant.

Sorry I can't be more clear.  It would be really nice to get someone who is
in the design end of the tire business to talk about this. but they probably
aren't driving Vanagons!

- Mike


Mike Finkbiner
mike_l_f@hotmail.com

"No man shall ever be debarred the use of arms. The strongest reason for the
people to retain the right to keep and bear arms is, as a last resort, to
protect themselves against tyranny in government."

    -- Thomas Jefferson