Date:         Thu, 17 Mar 2005 05:30:21 +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 -
Content-Type: text/plain; format=flowed

Larry said -

Chris,

Actually ... This looks like a pretty decent tire.

But not sure if I agree on the "2 ply" equals reinforced sidewall.

But not sure I disagee either.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Larry -

Reinforced is the confusing one, but here is the definition from General
Tire's web site

"Reinforced or XL (extra load) tires are specially reinforced tires. They
can carry higher loads than a tire of the same size.
Reinforced tires are designated on the Sidewall by the letters "RF", extra
load tires with the letters "XL".
Reinforced and XL tires require need higher inflation pressures compared to
standard tires."

The key is in the last sentance "higher inflation pressures".

I sort of grew up in the tire business.  My dad sold tires for years, and I
was in high school when he started selling bias-belted as the premium tire
(mid 60's), and then true radials.  After college I sold tires for Sears
before moving on to other things.  As others have said, the number of plies
is a holdover from 50 years ago before belted and radial tires.  Back then,
the standard (4-ply) passenger tire had a maximum inflation pressure of 35
psi.  Truck tires would go to 50 for C rated (6-ply) and 60 or more for D
rated (8-ply).

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.
Why drop the pressure?  Handling, comfort, tire wear or some combination of
those three.  Too high a pressure on the wider tire could wear the center
more then the edges.  Full pressure with a normal load would make the tires
stiffer, so they might not handle as well as the same tire at lower
pressure.  Like everything else it's a balancing act.

The Michelin mentioned in other posts, and the Guardsman in this one, are
newer designs.  They specify 44 psi maximum, and can handle heavier loads,
so they have a reinforced sidewall by General Tire's definition.  Both have
sufficient load ratings for a Vanagon.

If they handle well at 44 psi, I wouldn't be worried about the durability.
If you run at lower pressures, you will lose some of the load capacity and
the sidewalls will be more vulnerable because they protrude more.  That's
more of a problem for people who drive off road, or have to deal with
potholes.

My standard for the Vanagon is a minimum LR 93 IF you are going to run them
close to max pressure.  If you want to be able to adjust pressure down to
find the best handling and comfort level, you need to go to a higher load
range.  I'm more comfortable with a tire you can run at 48-50 psi on the
rear, because it needs to be more stiff than the front, but 44 is darn
close.  If you always run with a heavy load or tow a trailer, you should go
with a heavier tire.

The Firestone's that had all the problems on the Ford Explorer were being
run at something like 26 psi.

Confusing, no?  Truck drivers often adjust the tire pressure they are
running to match the load carried.

The folks who really have problems are running P metric tires with 35 psi
max pressure.  The only thing saving them is the fact that engineers are
conservative and all tires have excess capacity built in.

Your mileage may vary, I'm not a tire engineer nor do I play one on TV.

- Mike

Mike Finkbiner
'87 Westy (wearing Haaka CQs in 185R14)
Moscow, Idaho
mike_l_f@hotmail.com

"No man shall ever be debarred the use of arms. The strongest reason for the
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    -- Thomas Jefferson