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Help with tire pressure?

taxreliever

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My 37's on the 79 F250 show 65lbs Max Load when cold on the tire and I cannot find another reading anywhere else on either side of the tire......it just seems like a lot of pressure, especially in the summer. How do I know how much to put in?

Thanks for any help.
 

taxreliever

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Hi Ken,
I inflate to 75% of the rating on the tire, cold and not carrying a heavy load. Any more and it's like driving with solid tires :(

Thanks Roy.....but doesn't 65 seem high? My 36" super swampers on my 77 say 35 and I actually inflate them to that and it feels fine...not too hard.
 
Given what you use the truck for and the weight of it Ken I'd run it between 40 and 45psi - if you run less you'll find the sidewalls will flex a lot more on the corners and tyre wear will become excessive on the outside edges conversely if you run too high a pressure you'll find your tyres wearing excessively in the centre.

Her's a link to a tyre wear chart that will explain it better than i can - http://www.procarcare.com/includes/content/resourcecenter/encyclopedia/ch25/25readtirewear.html
 

taxreliever

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65 under Max Load, but if you're never carrying heavy loads, you can go to 48-50psi. The tires on mine say 80psi! cold, Max Load. I run at 60psi.

Dang....then why are my super swampers so low at 35?

Given what you use the truck for and the weight of it Ken I'd run it between 40 and 45psi - if you run less you'll find the sidewalls will flex a lot more on the corners and tyre wear will become excessive on the outside edges conversely if you run too high a pressure you'll find your tyres wearing excessively in the centre.

Her's a link to a tyre wear chart that will explain it better than i can - http://www.procarcare.com/includes/content/resourcecenter/encyclopedia/ch25/25readtirewear.html

Thanks Mark! I knew about the wear of under and over inflating, but like you said, I don't use it as a DD, don't haul with it, and the total mileage for the year is very low.....so I like the 40-45 number. These tires are so big and expensive, that I want them to last as long as possible.....reminds me of the trick I learned on here last year (from Ben or Austin) about armoralling the inside of the tires as well to make them last longer.
 
Last edited:

smokey

Hitech hillbilly
Staff member
I normally ran 50psi in the f250 the tires were rated 65 max load. They wore great and the ride was better than at 65. I did air up when hauling heavy loads.
 

taxreliever

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I normally ran 50psi in the f250 the tires were rated 65 max load. They wore great and the ride was better than at 65. I did air up when hauling heavy loads.

Thanks Randy.....I just checked the pressure expecting to put some air in the tires even though they didn't look like they needed much if any and all four tires read 65lbs.....that amazes me because when I took the 77 out a week or two ago (posted on the forum somewhere), the rear two tires only had 17lbs in them.
 

taxreliever

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Ken, it can't hurt to send an email the the manufacturer asking them. Tell them what your running the tires on and how often its driven. Give them the trucks weight too.

Thanks Mark....you mean the tire mfg? I drove this baby from SC with the exact 65lbs of pressure that's in them today and it drove just fine in town and on the highway.....a little bumpy on rough roads, but I just chalked that up to being the F250....maybe I should let some air out.
 

SuperCab

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The difference in pressure specs could just be different load ratings.

Any 8 ply rating light truck tire runs at 65 psi for max load capacity.

10 ply tires run at a whopping 80psi for max capacity, as has been said.

Your other tires are probably a 6 ply or less, therefore requiring less pressure.
 

taxreliever

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The difference in pressure specs could just be different load ratings.

Any 8 ply rating light truck tire runs at 65 psi for max load capacity.

10 ply tires run at a whopping 80psi for max capacity, as has been said.

Your other tires are probably a 6 ply or less, therefore requiring less pressure.

Ahhh...thanks for the clarity....didn't think there would be that much difference between the Interco Super Swampers and the Nitto Mud Grapplers, but I guess there is.
 

taxreliever

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Hi Ken,
so you can see by the replies that you're good to run anywhere between 15-20psi Below the Max Load rating. You don't use your beautiful trucks to haul , do you... :wavey:

The only hauling this thing does is me and my boys! :wavey:

So do I let some air out? Or just leave it alone at 65?
 

LEB Ben

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Running max psi without a load will cause it to bounce like an over full basketball. PSI is a correlation to load index and sidewall/ply construction...ie bias/radial, nylon/Kevlar/steel, ply count, etc. Intent of a TSL is to be able to flex (even the radials), and 65psi doesn't promote that...they'll have a softer rubber compound as well that will allow more flex. I'd assume at 65lbs is a load range D tire and the Swampers are probably a C. Typically, I like my tires to be 10-15% less than max psi...but I suppose technically you need to get a weight at each corner and figure what percentage that is of the max load capacity of the tire, then multiply that percentage by the max psi. But no one does that, they either back off a certain percentage or fill that baby right up to the max psi.
 

taxreliever

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Running max psi without a load will cause it to bounce like an over full basketball. PSI is a correlation to load index and sidewall/ply construction...ie bias/radial, nylon/Kevlar/steel, ply count, etc. Intent of a TSL is to be able to flex (even the radials), and 65psi doesn't promote that...they'll have a softer rubber compound as well that will allow more flex. I'd assume at 65lbs is a load range D tire and the Swampers are probably a C. Typically, I like my tires to be 10-15% less than max psi...but I suppose technically you need to get a weight at each corner and figure what percentage that is of the max load capacity of the tire, then multiply that percentage by the max psi. But no one does that, they either back off a certain percentage or fill that baby right up to the max psi.

Ok, going to let some air out for sure now....thanks Ben....and thanks everyone else.....always learning with vehicles...love it!
 

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