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Old 05-10-2014, 10:48 AM   #1
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Another tire question

I went through the search function for this answer and only got more confused.

I replaced my BFG AT's (285/75/16 E rated) with the same size Michelin LTX AT's.

When I first got the BFG's, they were inflated to 80psi, the max allowed on the sidewall. The ride was just awful, so I reduced them to 65 psi all around which helped.

Now that I have my new (expensive) Michelin's, the sidewall says max pressure is 80psi. But with that comes the same riding on rocks level of comfort. I don't have onboard air, so I don't have the luxury of airing down on bad roads.

The Van weighs in at just under 10k pounds, with me, a full load of fuel, gear and bourbon.

Any help on tire pressure would be appreciated.

thanks..

Tom
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Old 05-10-2014, 02:42 PM   #2
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Re: Another tire question

Might help if you can weigh the axles or even each tire. I doubt you have to run full pressure.
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Old 05-10-2014, 09:09 PM   #3
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Re: Another tire question

There are several threads about proper tire pressures. I run my toyo M/T's (80 psi max) at 65. It is rare that you will run a tire at its max psi. However, I do plan on bumping it up a bit, maybe just in the rear for long highway hauls to ~70. I go down to 35-40 when off road. It sounds like you had better results running at 65. Something else to consider are your shocks, how old? Brand? Springs....
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Old 05-10-2014, 09:46 PM   #4
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Re: Another tire question

When I first bought Michelins for my van, they were inflated to that psi as well. It felt like riding on ball bearings, with about as much directional stability as ball bearings. So, I called the tire guy and he said reduce the tire pressure down to, I believe, what REF said. I think it may even be a little less in the front... Anyway, thereafter my wife and I drove all through So.BC with new Michelins and loved them. From Sacto. to Shasta though it was weird, not good at all until in Shasta we reduced the tire pressure as recommended. Talk to your tire guy.
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Old 05-11-2014, 09:39 AM   #5
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Re: Another tire question

This is a pretty complex problem given that the bourbon will begin the trip but be lost little by little, basically making it impossible to balance the load properly for the entire trip. I suggest starting on the bourbon now so that thinking through the problem is easier. Best of luck.

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Old 05-11-2014, 11:31 AM   #6
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Re: Another tire question

Thanks all, for your responses. I think the bourbon may be the variable here, but there's no way to keep it constant. Unless I don't drink it, and what fun is that?
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Old 05-12-2014, 08:53 AM   #7
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Re: Another tire question

I'll give you the short answer since your van is the same as mine and tire size is the same.
55 front
60 rear.
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Old 05-12-2014, 09:45 AM   #8
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Re: Another tire question

Thanks ANZAC, maybe a dumb question, but why have less air in the front tires, when the front has more weight?

Tom
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Old 05-12-2014, 01:16 PM   #9
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Re: Another tire question

Quote:
Originally Posted by flyfisher
Thanks ANZAC, maybe a dumb question, but why have less air in the front tires, when the front has more weight?

Tom
My van has more weight in the back... 3740 front, 5420 rear.

The pressures for the stock tire sizes are higher in the back too, it assumes you will be carrying a big load there, but with a built out SMB, you already have quite a load in the back. I wouldn't worry too much about what your actual weight us, you just want to get to the right pressures for the larger tire size.

If you're interested in the process to get from the stock size pressures to those pressures I can point you at the thread. Sometimes I run 50 at the front, it is a little more comfortable.
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Old 05-12-2014, 02:11 PM   #10
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Re: Another tire question

Quote:
Originally Posted by flyfisher
Thanks ANZAC, maybe a dumb question, but why have less air in the front tires, when the front has more weight?

Tom
Tire pressure is probably most important as it affects the load carrying capacity without tires overheating, which can lead to catastrophic failure. For that reason I agree with Daveb that it's a good idea to weigh your van (or trailer, motorhome, etc....) in order to know how close you are operating to tire limits.

The vehicle manufacturer labels recommended tire pressure front and back (usually on driver door area) not only based on the van's Gross Vehicle Weight Rating but also that of each axle independently. As an example, my van's rear axle is rated just above 6000 pounds which requires the stock tires to be inflated to 80 PSI. The front axle is only rated just above 3500 pounds so front tires don't need as much air pressure to keep from overheating.

However, air pressure not only affects tire load capacity but it also affects rolling resistance and more importantly it affects handling. In my case the recommended front air pressure is much higher than necessary for the load according to Michelin data. But the right pressure is required to make the van handle properly otherwise it would oversteer (or at least under steer less than Ford wants).

I'd start by weighing the van, then looking up the Michelin load table for your tires, and then determine the minimum required pressure to keep them from overheating. I would then experiment with pressures above that to see when ride becomes unacceptable, keeping in mind Ford's approximate front-to-rear pressure bias to ensure right amount of under steer.
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