Date: Sun, 24 Jul 2005 21:55:49 -0500
Reply-To: John Rodgers <inua@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@CHARTER.NET>
Subject: Re: Calculating Proper Inflation PSI for Tires
In-Reply-To: <00c201c590b2$ff957310$d6834e45@t41>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Larry,
Thanks very much for the detailed explanation. Makes a lot of sense to
me. I'm going to go on your reccomendation of 40 Front, 48 Rear ......
until and if tire wear pattern dictates otherwise.
Thanks again.
John Rodgers
88 GL Driver
Larry Chase wrote:
>John,
>
>You asked for recommendations on the correct air pressures to use for your
>Michelin XCA 205/75/R14C tire on a 1988 GL Vanagon.
>
>Mark and Dennis made suggestions and my calculations are in the same
>ballpark.
>
>Larry Chase
>35-40 front / 45-48 rear
>- - -
>Mark Drillock
>36-40 front 43-48 rear
>- - -
>Dennis Haynes
>36 front / 40-45 rear
>- - -
>
>But I want to show how I did the math.
>
>To calculate proper tire pressure for a non stock size tire we need four
>things:
>
>1) VW Silver Sticker (door jam) tire info
>2) Tire Load Inflation Tables (Weight a specific load range tire carries at
>various psi values)
>3) Max Load Capacity & Max Inflation Pressure for the OE Tires
>4) Max Load Capacity & Max Inflation Pressure for the current tire.
>
>Your starting point is the VW Silver Sticker (on door jam) from which you
>determine the manufacturer's target tire load capacity with safety reserve.
>By looking up the specified load capacity of the OE tire combinations in the
>load inflation tables, you then match the new tire inflation to that value.
>Doing this identifies the safety reserve VW used.
>
>Fortunately I have been able to acquire the "Load Inflation Tables" and
>because of the various tire info suveys folks responded to (Silver Sticker,
>GVWR & OE Tire)I now have the data needed.
>
>Your Vehicle: 1988 GL Vanagon
>
>Original Equipment Tire Option 1 (if we used the other OE Tire Option for
>that year we would get similar results)
>
>Size: 185R14 C 6PR
>Brand: Continental
>Model: Transport RS 771
>Load Index: 99
>Load Capacity: 1710 lbs
>Max Inflation Pressure: 55 psi
>
>The VW Silver Sticker for a 1988 Vanagon = front tire inflation of 39 psi /
>rear inflation of 48 psi for this tire.
>
>Using the "Load Inflation Tables" this tire has the capacity to carry ~1400
>lbs at 39 psi & ~1600 lbs at 48 psi.
>
>BTW ... the vehicle GAWR Capacities 1323 lbs front and 1433 lbs rear per
>tire.
>
>The difference is the safety margin VW determined was needed (1323 vs 1400
>frt & 1433 vs 1600 rear)
>
>So for any tire size other than OE sizes .. we calculate what PSI is needed
>to carry ~1400 lbs & ~1600 lbs.
>
>Example .. your current tire
>
>Michelin XCA
>205/75/R14C
>Max Load Capacity: 2270 Lbs
>Max Inflation: 65 PSI
>
>Consulting the "Load Inflation Tables" we see something that looks like
>this,
>
>Inflation PSI vs Load Capacity in lbs
>
>35 / 40 / 45 / 50 / 55 / 60 / 65 psi
>1415 / 1555 / 1695 / 1835 / 2110 / 2115 / 2270 lbs
>
>Since we need to be able to carry 1400 lbs frt & 1600 lbs rear the correct
>PSI values for this tire are;
>
>Front = 35 psi
>Rear = 45 psi
>
>>From that point you would make minor adjustments for actual load, handling
>and ride.
>
>I'd suggest a range of
>
>Front = 35-40 psi
>Rear = 45-48 psi
>
>Hope this made sense and wasn't too terribly boring.
>
>
>Larry Chase
>
>www.roadhaus.com
>www.roadhaus.com/shops.html
>www.roadhaus.com/tires.html
>
>
>
>
>
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