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Old 04-02-2013, 08:59 PM   #1
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Tire Pressure ?

I have BF Goodrich 31570R17 All Terrain T/As. Max tire pressure is 50 on the tire. What are you boys running on these tires?

I have been running 55. I would swear I saw that was the recommended pressure in the documentation I got with the vehicle. However, when I look thru the binders I can not find this number.

When I look on the door label it says 45 front, 50 rear.

Mike
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Old 04-02-2013, 09:46 PM   #2
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Re: Tire Pressure ?

Door labels can misinform you. You might be reading what the pressure is for a stock tire. It's what is on the tire that counts. Then there is a formula depending on how heavy the weight that is on each tire. But there is also a rule of thumb and a few other ways to pick the correct weight. For years I ran a D rated tire that was under the safety rating for my heavy van. I now run an E rated tire. It's also important that the rim itself is rated for the weight on each tire. Each tire manufacture/model can be different. My 285 Toyo's were 70-75 rear, and front 60-65 with a max of 80 for the tire at full weight which escapes me right now. I have a heavy van.
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Old 04-02-2013, 11:19 PM   #3
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Re: Tire Pressure ?

I think that BFG has a load index of 121 and at 50 psi is rated for 3195 lb. That should be plenty, I wouldn't run more than 50 and you could probably get away with a bit less and your ride won't be as harsh.

This has been posted before but use this formula: (max psi/max load)*(real load) + 15% safety margin or whatever your comfortable with. Ideally you should know the weight over each axel.

For example my rig weighs 10,000 pounds and the tires are rated for 3860 at 65psi. So,
(65/3860) x (5,000/2) = 42 psi
42psi + 15% = 48 psi
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Old 04-03-2013, 12:02 AM   #4
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Tire Pressure ?

My bfg a/t triple ply e rated 16" tires show 80psi max cold.

Door jam recommends 60 front/80 rear cold, but probably for the stock 16s.

Am I good to go with 60/80?
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Old 04-03-2013, 12:14 AM   #5
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Re: Tire Pressure ?

Quote:
Originally Posted by Ocsmb
My bfg a/t triple ply e rated 16" tires show 80psi max cold.

Door jam recommends 60 front/80 rear cold, but probably for the stock 16s.

Am I good to go with 60/80?
If those are 285/75s then those tires are rated at 3750lb at 80psi. Figure out how much your van weighs and do the math. Discount Tire and Auto has tire load/inflation tables available if you ask. I can't find them on their website.
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Old 04-03-2013, 12:16 AM   #6
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Re: Tire Pressure ?

Quote:
Originally Posted by silvett1
I have BF Goodrich 31570R17 All Terrain T/As. Max tire pressure is 50 on the tire. What are you boys running on these tires?
I run the exact same tires on my '97 V10 E350 EB SMB 4X4 and on my '05 F250 Crew Cab 6.0L 4X4 (it is on the third set) at typically 45 Psi on all four corners. The truck hold 160 gals of fuel and is often loaded down to where it is well into the stock overload springs and much heavier that the van will ever be - when that loaded I sometimes set them at 50. In the dirt, I air down to 25 Psi often.
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Old 04-03-2013, 12:28 AM   #7
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Re: Tire Pressure ?

I'd certainly back off from anything _over_ the maximum rated pressure listed on the sidewall.

I'm running 275/70R18 BFG Rugged Terrain T/A (max 80 psi), and had them at whatever pressure I calculated from their rated load and my actual load. I found the sidewalls felt a little soft like that, leading to some squirrelly handeling. So I took them up to 78 psi and much prefer them there, no matter how the van is loaded. I'm not seeing any strange wear yet in 10k miles. YMMV
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Old 04-03-2013, 02:30 AM   #8
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Re: Tire Pressure ?

Hello guys,

I'm a little surprised how many of you seem to inflate your tires with several different pressures not always regarding the right weight on each axle.


I worked many years by Michelin here in Europe and I must remember how it's important to run with the right pressure. It's not only a security matter, where low pressure makes the tire warm up with risk of rupture of the tire carcass. If you inflate your tires to much, the breaking distance will increase, the traction will be reduced and your mileage of the tire set will decrease a lot! 10% over pressure will decrease mileage of the set more than 15%, 15% more than 25%!

There is only one way to determine the right inflating pressure: weigh each axle of your loaded van and read load/inflation/speed tables of your tire manufacturer. You will increase your security and save your money...
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Old 04-03-2013, 12:44 PM   #9
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Tire Pressure ?

Quote:
Originally Posted by JoeH
I think that BFG has a load index of 121 and at 50 psi is rated for 3195 lb. That should be plenty, I wouldn't run more than 50 and you could probably get away with a bit less and your ride won't be as harsh.

This has been posted before but use this formula: (max psi/max load)*(real load) + 15% safety margin or whatever your comfortable with. Ideally you should know the weight over each axel.

For example my rig weighs 10,000 pounds and the tires are rated for 3860 at 65psi. So,
(65/3860) x (5,000/2) = 42 psi
42psi + 15% = 48 psi
My bfg a/t e-rated 285/75/16 are 3750 at 80psi
Ford factory sticker inside door column states:
Gawr is 4050lbs front; 6084lbs rear

(80/3750) x (4050/2) = 43.2
43.2 + 15% = 49.68 psi front

(80/3750) x (6084/2) = 64.9
64.9 + 15% = 74.7 psi rear

I suck at math. How's that look?

Also, the ford door column sticker gawr doesn't account for the added smb conversion weight correct?

Finally, would it make a big difference in tire performance to weigh the van loaded like you normally would travel with it and recalculate the correct tire pressure or are we splitting hairs?
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Old 04-03-2013, 01:10 PM   #10
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Re: Tire Pressure ?

Quote:
Originally Posted by Ocsmb
...Finally, would it make a big difference in tire performance to weigh the van loaded like you normally would travel with it and recalculate the correct tire pressure or are we splitting hairs?
i would assume yes on this. i get my alignments in my tl (car has toe in issues) with my fatass in the drivers seat so that everything is at its most perfect setting as it will roll down the road. ill be doing the same with the van when the day comes both with alignment and pressures.
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