Date: Thu, 24 Apr 2003 18:21:16 -0700
Reply-To: Todd Last <rubatoguy@MINDSPRING.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Todd Last <rubatoguy@MINDSPRING.COM>
Subject: Re: Max Load Rating Calculation
Content-Type: text/plain; charset=646
Don't know if it is correct or not, but here is how I would figure it out.
Take the higher GAWR and divide by two. (3042/2 = 1521) This is your maximum load per tire at maximum axle load. You want to make sure that your tire can carry this load at maximum inflation at a minimum. 1521 equates to a load index of 95. (Assuming you are running at max inflation pressure)
So I would say that a load index of 95 would be a bare minimum. Or 102 for a P-metric tire - P-metric have to be de-rated by 9%)
According to NTSA, "FMVSS 110 requires that the vehicle’s normal load on each tire must not exceed 88% of the tire’s maximum load rating as marked on the sidewall of the tire."
Being very conservative, if you take the GAWR as your normal load, that would mean that you would need a tire with a maximum load rating of 1728 (1521 being 88% of 1728) to be in compliance with FMVSS 110.
This equates to a load index of 100.
So, depending on your preference of a saftey factor, picking a tire with a load index of between 95-100 sounds like the way to go - If you run at maximum inflation pressure. (For P-metric fans that would be 102-109)
I'm not sure where the 97 index came from, but my guess it is the GAWR (95 load index) with the load adjusted for the standard inflation pressures for the Vanagon. (Bumping it up to 97)
Since the maximum load a tire can carry is proportional to the tire pressure, you need to adjust your load rating of the tire according to the inflation pressure you run.)
That's my take on it, anyway.
Todd
'88 Westy
-------Original Message-------
From: Larry Chase <lchase@ATTGLOBAL.NET>
Sent: 04/24/03 07:07 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Max Load Rating Calculation
>
> Volks,
I'd like to better understand how we get to the Maximum Load Rating Tire
recommendations for our Vanagon.
Example, the generally agreed upon Vanagon Tire specification is: Load
Index: 97 (1609-1652 lbs.) or Higher
Exactly how do we get from GVWR or GAWR to the Load spec of
1609-1652lbs.
I know there is a safety margin figured in, but I'd like to know
specifically how to do the actual math.
My 1990 Syncro Westfalia has the following load specifications.
GVWR LB 5512
GAWR LB Front 2866 / Rear 3042
GVWR (Gross Vehicle Weight Rating):
The Maximum permissible weight of the unit, including
the Unloaded Vehicle Weight plus all fluids, cargo,
optional equipment and accessories. For safety and
product performance, do not exceed the GVWR.
GAWR (Gross Axle Weight Rating):
The total weight each front/rear axle, suspension
and tire system is designed to carry. When loading
the unit, care should be taken to balance cargo
weight in consideration of the GAWRs.
Thanks,
Larry Chase
Email: RoadGuy@RoadHaus.com
Web: <a target=_blank href="http://www.RoadHaus.com">www.RoadHaus.com</a>
What: North American Road Trip
How: RoadHaus - 1990 VW Westfalia Syncro
Today: Denver, CO
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