Tire pressure?
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Senior User
Joined: Jan 2014
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From: Thousand Oaks, CA
Tire pressure?
So I'm pretty much a noob to big trucks and big tires, so I'm wondering what you guys think. I have my sorta new to me 02 7.3 Ex, and the PO had put Hankook Dynapro 315/75/16 tires on it, and they have a lot of life left in them, and I'd like to keep it that way for as long as I can.
The question I have is this: The door tag says 50/50 psi and the tire's rating is at 50 psi as well. The rears are starting to wear a little more in the middle though. What pressure should I run these at to maximize their lives?
Whaddayathink?
Thanks,
Curt
The question I have is this: The door tag says 50/50 psi and the tire's rating is at 50 psi as well. The rears are starting to wear a little more in the middle though. What pressure should I run these at to maximize their lives?
Whaddayathink?
Thanks,
Curt
Laughing Gas
Joined: Feb 2014
Posts: 965
Likes: 36
From: Greater Seattle area
Over-inflation causes the wear in the middle. The door tag is for factory sized wheel/tire combo. If you do not have factory tires on the rig, you may be over inflating by running at the Max as labeled by the side of the tire. If you aren't towing at high capacities, do not run the tires at max psi. Old rule of thumb I've always heard is to run 3/4 the max PSI (so about 38 in your case) and adjust from there.
Someone feel free to jump in here if the 3/4 rule is not the most recommended.
Someone feel free to jump in here if the 3/4 rule is not the most recommended.
Laughing Gas
Joined: Feb 2014
Posts: 965
Likes: 36
From: Greater Seattle area
From Hankook website:
"Generally, the optimum inflation pressure is about 90% of the maximum level. For high-speed driving, drivers are recommended to use a higher than normal pressure."
45 PSI
Welcome to Hankook Tire
"Generally, the optimum inflation pressure is about 90% of the maximum level. For high-speed driving, drivers are recommended to use a higher than normal pressure."
45 PSI
Welcome to Hankook Tire
Post Fiend
Joined: Mar 2009
Posts: 11,798
Likes: 14
From: Mt. Shasta California
If the tire rating is 50 PSI it sounds like you have C rated or maybe even passenger car tires. In that case you will have to drive with your hands at 10 and 2 o'clock with 2 fingers crossed. Often dealers and PO's will put those on before selling.
Laughing Gas
Joined: Feb 2014
Posts: 965
Likes: 36
From: Greater Seattle area
--T
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Senior User
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From: Thousand Oaks, CA
I'm splitting the suggestions in half, and running 42 psi and we'll see how it goes for a while. 
Also, the tires have a Load Range D marking on them, but I generally drive with both hands anyways. Ya never know what you might encounter on the mean streets of LA.
Thanks for the input everyone.
Curt
Also, the tires have a Load Range D marking on them, but I generally drive with both hands anyways. Ya never know what you might encounter on the mean streets of LA.
Thanks for the input everyone.
Curt
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Post Fiend
Joined: Mar 2009
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From: Mt. Shasta California
That is an 8 ply rating tire with a 121 load index. D rated normally is rated at 65# and C's at 50# but if it says D it should be OK.
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From: Media PA
Good point Brent, and those rule of thumb numbers are accurate for stock sized tires. With wider tires the numbers do change as the footprint of the tire increases, the higher the square inches of contact patch the less pressure is required to support the load. My E rated (3750lb) 305/70R18Es (12.80" wide) meet their max ratings at 65 PSI.
Thread Starter
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Senior User
Joined: Jan 2014
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From: Thousand Oaks, CA
Good point Brent, and those rule of thumb numbers are accurate for stock sized tires. With wider tires the numbers do change as the footprint of the tire increases, the higher the square inches of contact patch the less pressure is required to support the load. My E rated (3750lb) 305/70R18Es (12.80" wide) meet their max ratings at 65 PSI.
The tires on the Boeing 777 that I fly are pretty big, but would probably not look out of place on some of the FTE member trucks. The pressure in them is about 225 psi IIRC. They carry 650,000 lbs... But of course there's 8 of 'em!
Curt
Post Fiend
Joined: Mar 2009
Posts: 11,798
Likes: 14
From: Mt. Shasta California
Good point Brent, and those rule of thumb numbers are accurate for stock sized tires. With wider tires the numbers do change as the footprint of the tire increases, the higher the square inches of contact patch the less pressure is required to support the load. My E rated (3750lb) 305/70R18Es (12.80" wide) meet their max ratings at 65 PSI.
Post Fiend
Joined: Mar 2009
Posts: 11,798
Likes: 14
From: Mt. Shasta California
From Hankook website:
"Generally, the optimum inflation pressure is about 90% of the maximum level. For high-speed driving, drivers are recommended to use a higher than normal pressure."
45 PSI
Welcome to Hankook Tire
"Generally, the optimum inflation pressure is about 90% of the maximum level. For high-speed driving, drivers are recommended to use a higher than normal pressure."
45 PSI
Welcome to Hankook Tire
Moderator
Joined: Jul 2010
Posts: 12,050
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From: Media PA
Ummm, Yeah......
There are other little tricks folks have used over the years to dial in tire pressure. Like covering the tread face (on a 6 to 12" section) with chalk or paint, evenly applied of course and then driving forward slowly in a straight line till the wear pattern shows itself. Then adjust pressure to get the wear to show even across the tread face. Old school for sure, but it works.
Laughing Gas
Joined: Feb 2014
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From: Greater Seattle area
Someone make this happen!
Fleet Mechanic
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From: Danbury, CT
Goodyear, Michelin, Continental? You put chains on 'em in the winter?