Tire Load Index Charts? (1 Viewer)

[srgould41]

I know I read this either here or on Pirate, but after two days of searching I can't find it.

I am trying to find a tire load chart that shows pressure/load for given sizes. So when installing larger tires I want to get an idea of proper tire pressure for highway driving.

Anyone know where to find a generic type chart? I am getting tired of triail and error... I am not worrying about air down pressure, already have that figured, just highway.

Thanks,

Steve

 

[Poser]

Anyone know where to find a generic type chart?

 

[joeyg1973]

OK how do you make the google smilie?

 

[BDSeff1fitty]

Let me google that for you

^^ its a link...

 

[joeyg1973]

Let me google that for you

^^ its a link...

That's fxxxing hilarious.

 

[srgould41]

You guys are so funny.

I have been hunting on Mud and Pirate for 2 days and Google for longer. That page from "Let me Google it for you" is all purple links. Meaning I have already gone to each of those links...

I HAVE found a chart at Goodyear's web site which says I should be running at 15 psi on the street. Um, I don't think so.

So I will I will leave you posers (pun intended Poser) to laugh at me while I continue my search.

 

[BDSeff1fitty]

i think tires usually say this on them dont they?

 

[MoCoNative]

I went through the same stuff, my T-100 has 16 inch tires on it now, but originally came from the factory with 15 inch tires. These guys pointed me towards some calculations and such, but nothing really produced a pressure I liked.

The door plate calls for around 30 PSI or something in the stock 31 inch tires. I felt that was too low in a load range D truck tire, with a max pressure of 65 on the sidewall. When I ran them at max pressure, they were very harsh riding for the stock truck, unloaded, and the tread was crowned pretty good. I have settled on mid 40's for pressure now, and I have been happy. It really is trial and error on this one.

 

[65swb45]

In the end a reference chart is JUST A REFERENCE chart. YMMV

I learned almost 20 years ago that NONE of my trucks would ride properly or wear properly with recommended inflations. I run a good bit less than Rx and have never had an issue.

IMO, a good starting point is to do a 'puddle' contact patch test. It's pretty much a given that virtually no tire will make a full width contact patch at Rx tire pressure. My new 33's on my 40 will not make full width contact at 22psi, so I am still experimenting, incrimentally.

I'm gonna PM a couple of tire guys I know to chime in on this one.

 

[srgould41]

MoCoNative, that is what I have been doing so far. I just pick a pressure and drive it. I don't do much on road driving, just to and from wheeling sites. I just want a safe pressure on the road and I want to limit uneven wear.

So let me start over and ask my question more directly.

I have a stock 40 with 30x10.5x15 Cooper Discoverer M+S tires. The PO put them on before he sold the rig to me. I have no clue what the pressure should be. I can't find any info on the Cooper web site. It basically says to seek advice from a tire expert. Does anyone have similar size tires and have a good working pressure?

 

[wct49]

Remember a couple of things about air pressure.

#1 The tire has now idea what it on.
On my 80 running a LT31575-16 Load Range D, the tire calls for 50 psi for max load carrying capacity.
The 80 with its OE tire wanted 32.

I am running 45 psi in the tires. Keeping my steering response up and with all the fun extras on the truck, it sure weighs more than it did when it came of the boat from Nippon.

#2 Manufactures are all about comfort. We see this alot on trucks and suv. They want it to ride like a car. One way to fix that is with air pressure. The tire may hold max psi of 44 but the manufacture wans the truck to ride like a car so the want 35 psi. Ask Ford about that with the Firestone recall. Ford wanted 30psi in the Firestones for ride and comfort. Great when you are going to work, not so great when you, spouse and three cracker eaters are going to Disney for the week.

Just remember low air pressure kills tires. Mostly because people do not routinely check their psi. The car wants 30psi so thats what they run. Then there is a cold snap or they go 6 months without checking them. Now the 30 psi tire is at 18psi.
Not Good.

 

[MoCoNative]

MoCoNative, that is what I have been doing so far. I just pick a pressure and drive it. I don't do much on road driving, just to and from wheeling sites. I just want a safe pressure on the road and I want to limit uneven wear.

So let me start over and ask my question more directly.

I have a stock 40 with 30x10.5x15 Cooper Discoverer M+S tires. The PO put them on before he sold the rig to me. I have no clue what the pressure should be. I can't find any info on the Cooper web site. It basically says to seek advice from a tire expert. Does anyone have similar size tires and have a good working pressure?

That makes a difference to me. I can say that I have run LT235 75R15 tires on my 40 for years, also on my 60. These are load range C tires. Similar sized tire, similar rating to your Cooper tires I assume. These were daily drivers, and I found that max pressure to 10 pounds below was best for them. I don't think you would go wrong in that window. Only issue would be the contact patch, but you may never get it flat with that wide of a tire, if you are running a narrow rim.

Sure, they rode kind of harshly at high pressure, but my 40 especially, was always very stable at the higher tire pressure on the highway.

 

[srgould41]

I guess I should just air them up to max, jump on the freeway and drive a bit, lower the tires 2 psi, drive some more, etc...

Thanks for all the advice.

Steve

That makes a difference to me. I can say that I have run LT235 75R15 tires on my 40 for years, also on my 60. These are load range C tires. Similar sized tire, similar rating to your Cooper tires I assume. These were daily drivers, and I found that max pressure to 10 pounds below was best for them. I don't think you would go wrong in that window. Only issue would be the contact patch, but you may never get it flat with that wide of a tire, if you are running a narrow rim.

Sure, they rode kind of harshly at high pressure, but my 40 especially, was always very stable at the higher tire pressure on the highway.

 

[Poser]

I have a stock 40 with 30x10.5x15 Cooper Discoverer M+S tires. The PO put them on before he sold the rig to me. I have no clue what the pressure should be. I can't find any info on the Cooper web site.

Have you tried calling Cooper Tire and requested to talk with one of their graduates from Tire College?

 

[srgould41]

Tire College

No, I have not called Cooper. Not a bad idea though. I am beginning to think I am making a mountain out of a mole hill.

Have you tried calling Cooper Tire and requested to talk with one of their graduates from Tire College?

 

[Texican]

Mark's puddle test is purty good however I would choose to err on the high side, almost all of the Firestone/Explorer roll overs were caused from Ford posting too low a pressure on the Explorer to make it ride like the car platformed SUV's instead like what it was .... a truck....higher is better for fuel mileage also...

 

[srgould41]

I looked on the tire sidewall. 30x9.5x15, load range C. 1990 lbs at 50 psi.

I made my own pressure chart. At 1000 lbs per tire the pressure should be 26 psi. Using heavier front and lighter rear maybe 30 psi front and 25 psi rear.

Lots to ponder.

 

[BDSeff1fitty]

I looked on the tire sidewall. 30x9.5x15, load range C. 1990 lbs at 50 psi.

I made my own pressure chart. At 1000 lbs per tire the pressure should be 26 psi. Using heavier front and lighter rear maybe 30 psi front and 25 psi rear.

Lots to ponder.

so yesterday you were clueless and now after just 1 day you have your own pressure chart. i would love to see what you come up with after 7 days.

 

[srgould41]

I would much rather have found an industry one. Who knows if mine is even correct. I just read the load versus pressure and extrapolated. I don't know if that is correct or not, but it seemed about what I would have expected. It's only a starting point anyway.

so yesterday you were clueless and now after just 1 day you have your own pressure chart. i would love to see what you come up with after 7 days.

 

[MoCoNative]

You are over thinking this, seriously, first, a loaded up 40 will be over 4000 pounds. So you are marginal on your 1000 pounds per tire. Put 40 -50 PSI in each tire and you will be fine. Hell pick 45 just for fun. That's an easy number to remeber when airing back up at the end of the day. All will be fine. I usually ran 50 in all of mine through school and such because I was after those elusive MPG's. A 40 will never ride great, they will ride rough no matter what.