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Old 07-29-2008, 06:03 PM   #11
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Also, here is the direct link to the Goodyear table.

http://goodyear.com/rv/pdf/rv_inflation.pdf

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Old 07-29-2008, 07:04 PM   #12
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And finally, here is a table from TOYO for RVs. Only a couple of tires are close to ours, but the inflation table is quite similar to the others. For example, it shows that you can use 50% of the maximum psi for a tire load that is 61% of the maximum load. So a tire that's rated at 3200 lbs. at 80 psi could be inflated to 40 psi for a load of 1952 pounds per tire. I'm not an expert, but my empty van sure drives a lot nicer inflated to 45 than it did at 65 psi.


http://www.toyo.com/pdf/rv_inflation_tables.pdf
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Van Weight 8,100 pounds, added one rear leaf spring, BFG AT KO LT265/70R17 E Tire press 50psi.
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Old 07-31-2008, 10:57 AM   #13
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I sent a message to Continental asking for a load inflation chart. And here is the reply:

Dear M.,

[Web Inquiry: 080729-000082]

We do not offer a load/inflation chart for passenger, or light truck
applications. If you have a specific load/inflation question, please reply;y
with the details for assistance.


I guess I have to send them specific weight and tire information and they will answer for that weight only.

Mike
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Old 07-31-2008, 04:42 PM   #14
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I called BF Goodrich also and finally talked to a tech person that new what he was talking about. His info pretty much agreed with the RV tables that i posted links for. He was going to send me a table via email, but never did.

Steve
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Old 09-20-2008, 09:58 PM   #15
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The tires that Craig at S K has on my 4X4 build says " LT265/70R17E Toyo open Country A/T tire(31.6 inch OD X 10.6 wide, 3,195 lbs. load rated at 80 PSI each) mounted on 17X8 wheels"

Doing the math: 3195/80=39.9. If I air down to 30psi then each tire will support 1200#. My van is heaver than 4800#. Is that ever a problem? Am I looking at this right? Do I need tires that support more weight such as bigger tires? I had told Craig I did not want huge tires and did not want to be real tall.

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Old 09-22-2008, 09:45 PM   #16
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Angel,

Check out the tires on my van in my gallery.

They are load rated much higher than required. And not too big.
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Old 09-22-2008, 10:41 PM   #17
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j.Whitbread, Your van looks great and the tires look good and not too big. I could live with them. I think your tires are made by Toyo. I looked them up: 285/70/17 Toyo AT max load is 3750 @ 80 PSI. Sounds good to me. Thanks for the info.

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Old 09-24-2008, 09:21 AM   #18
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Airing down (30 psi or below) is for offroad only. My rule of thumb is 30 mph max for short stretches, in general I try to stay in the 20s. (*my experience is with Jeeps which are very much lighter)

The problem with the above is that it generates excess heat and the heat can damage your tires, causing a breakdown later even with correct pressure at speed.

I would guess that the load rating/pressure is the same for highway speeds (e.g. if you run below the rated pressure for the weight at highway speeds you are likely causing heat damage to the tire that will show up then or later in a seperation or blowout) but I'm no expert- which brings me to my questions:

Is there any reason apart from ride quality to not to run max cold pressure?
Is it any safer to run max cold PSI (overkill for safety xx% > 15%)?
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Old 09-24-2008, 12:26 PM   #19
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Quote:
Originally Posted by jage
Is there any reason apart from ride quality to not to run max cold pressure?
Is it any safer to run max cold PSI (overkill for safety xx% > 15%)?
Two more reasons not to run max cold pressure:

- First, at higher than needed pressures, you tend to wear out the middle of the tread. At the ideal tire pressure, the tread lays flat on the road. Higher pressure push the middle out, lower pressures allow the middle of the tread to pull in and then wear the outer edges.

- Second, higher pressure reduce or eliminate the ability of the tire to bend around an obstacle (like a rock). Envision low pressure tires forming around obstacles. Now envision a high pressure tire acting more like a solid - and more likely to be damaged by the obstacle.

The tire gets harder at higher pressures. Less flexing, less heat, less rolling resistance.

Who knows? Maybe the higher tire pressures that wear out the middle of the tire actually increase fuel economy enough to offset the cost of early tire replacement. And the both effects are marginal for small changes in tire pressure.

If we get a dozen SMB's and all weigh the same and have the same tires, we could test various tire pressures for the next 50-100,000 miles and be able to answer some of the questions.

Or we could just run the pressure the tire company suggests for our weights. Or, like I did, calculate a pressure based on max ratings and actual weights.

Mike
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Old 09-24-2008, 05:02 PM   #20
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We have done a lot of research on tire pressure and rolling resistance in our efforts to get max mileage out of our hybrids, and we had to learn quickly to keep our OE Prius tires from wearing incorrectly.

One thing we learned was that pressure that is too low will wear the shoulders of the tires, but now, with steel belted tires, pressure at or below the max cold pressure do not cause adverse or increased wear in the center of the tread. In the past, with non-steel-belted radials as tires went up in pressure they would become "rounder" and that would cause center tread wear.

Higher pressure can decrease the ability of a tire to bend around an object, This may or may not be a problem, depending on the object and the surface the object is on. There are enough variables there that it is hard to decide whether you want the tire to bend around the object, crush the object, or push the object, or which would help avoid tire damage.

We have more than 200k miles on Cooper Discoverer ST tires at max cold pressure on and off road, and never a single tire problem.

We have 46k miles on a set of Goddyear Integrity tires at max cold pressure all on the road, and have had two leaks, but no flats.

The number one reason to adjust tire pressure is for load.
From there you can adjust for ride comfort, traction, and fuel economy.
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