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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