Date: Fri, 9 Jun 2000 16:18:14 -0400
Reply-To: Dave Katsuki <katsuki@MAK.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dave Katsuki <katsuki@MAK.COM>
Subject: Re: tire pressure
Content-Type: text/plain; charset="us-ascii"; format=flowed
Unca Joel,
Full agreement, especially with the intellectual power of the tire changers!
Just recently, I caught one trying to jack the rear of my van up with one
jack under the engine. (Hey, it was metal, right?)
Another way to evaluate the inflation pressure (assuming you've got tires that
have load ratings higher than the weight at each corner of the van), is to
observe
wear difference between the outer edges of the tires and the middles.
If the pressure is right for the width of tire and the weight of the van,
the tread wear
across the width of the tire will be even. If the pressure is too high
for the weight
of van, the middle will wear faster, and conversely if too low, the edges
will wear faster, especially with stiff sidewalls.
(Imagine a really light car with super wide tires, inflated to max tire
pressure,
and you can easily see that only the middle of the tire would contact the
road.)
Not the fastest test, though, and if your toe-in is wrong, wear
differential caused by tire pressure will be
confused by more rapid wear at outer or inner edges caused by wrong toe in.
Other tradeoffs - for a heavy tall van like ours, you really want stiff
sidewalls, which
means lots of pressure , which means a narrower than 205R tire might be
better.
6 or 8 ply sidewalls are probably always better. A lower aspect ratio
tire (e.g. 70 series)
is probably stiffer for a given pressure, so 205-70R14 is probably better
than 205R14,
given the same ply side walls. I bet a 205-60R15 would be great if
someone made it in the right load
range.
Dave
90 Westy
At 12:28 PM 6/8/00 -0500, Joel Walker wrote:
> As for the possiblity of the tire pressure on the door jamb being somehow
> outdated because the Van is 10 years old... it seems to me that VW
engineers
> considered both the weight of the Van and the tire before recommending a
> tire pressure.
very true .. for the tires that came on the bus from the factory. for ANY
other tires, we just don't know ... except from the tire make themselves. vw
did NOT put ALL tires that will fit or function on that sticker. and they
couldn't possibly have known what tires would be designed and built ten
years later nor what the capabilities or recommended pressures of those
tires would be.
so my point is: the sticker is valid ONLY for the tires (or exact
replacements) that came on the van. for any other tire size or brand or
model, you should (in my opinion) go by the tire itself.
trouble is, the tire folks aren't always the smartest workers in the world,
and they'll try to sell you 'passenger car' tires cause they fit. but the
Max Load or Load Index is not sufficient for good handling on the vanagon.
so listening to tire sellers is like listening to sellers of any product:
you have to take what they say with a grain of salt ... and always always
remember that they are trying to SELL you something. and that they do NOT
have to drive the bus after the tires are on it.
The way that the tire variability is controlled for over the
> years is by load index... the recommended pressure on the door jamb
assumes
> you are using a tire that meets the recommended load index.
how so? where is the Load Index even mentioned on the sticker? and are you
sure the government hasn't changed the specs in the last ten years? :)
> the tire side wall profile looks.... but if I want to go below the
recommed
> pressures on the door jamb, I will consult with the tire dealer who can
> provide minimum pressures (for the weight of the vehicle) from the tire
> manufacturer. Establishing a minimum pressure this way may be more
accurate
> than your 80% guideline.
then either you have smarter tire dealers where you live, or you trust your
tire dealers a lot more than i trust these kindergarten-dropouts around
here. my experience and stupidity in the past has come up with the 80
percent guideline, in addition to talking to the one tire dealer in
birmingham that i do trust. it works for me. each of us has to find the
solution that works for them ... your solution is to ask tire dealers. mine
is otherwise. and i still say the sticker isn't supposed to be information
for anything other than the tires that came on the bus. but everyone has to
make up their own minds.
joel
driving buses since 1970, and vw's since 1958.
