Cooper H tire inflation

[orbsah]

Hi all - I'm kinda confused on the correct tire pressure I should be using. Tires are Cooper Roadmaster RM170 215/75R17.5. During my PDI, the dealer said inflate to 110psi. Now checking the Roadmaster website and I'm seeing some conflicting info. I realize I should have each tire weighed separately to know the true weight at each position, but for this discussion let's simplify it and say the MAX load on any one tire would be half of the 7K axle rating = 3500lb. Again, ignoring the pin weight for this discussion. . . .

I found a chart online that says for these tires, the MAX load for dual tires is 4540 @125psi (obviously not loading these tires that much):


Then I found another chart that indicates for 3500lb load, the pressure should be 90psi:


Knowing that I should be loading each tire well below the 3500, doesn't this indicate that even 90psi is too much?

Thanks for the help!

[geotex1]

What does the sticker say on the side of your trailer?

[orbsah]

Well now it's getting more confusing. . . .

The sticker on the side of the trailer says 110psi BUT for ST235/80R16 tires which is not what I have.


And I just checked the pressure in these tires (they're cold) and they're actually inflated to ~120-125psi contrary to what my dealer said.

[andrewssteve]

The sticker on the side of the trailer says 110psi BUT for ST235/80R16 tires which is not what I have.

Wow. I would think the incorrect sticker violates some reg/rule/law. Seems to me GD has goofed up badly here.

-Steve

[Second Chance]

You highlighted the dual application number. The tires on our trailers are not used dual - that's where wheels are mounted in pairs like on the rear axle of our trucks. You should use the "Single" numbers. That said, I would probably stick with the 110 PSI on the trailer sticker as mentioned by @geotex1 .

Rob

[geotex1]

My recommendation is that you call GD. The tire pressure placard is NHTSA-mandated and promulgated in the CFR. However, I don't know the intricacies of its application to RVs or repercussion for OEM mismatch. Obviously consumers can deviate after the sale.

[orbsah]

Thanks everyone - I really appreciate your feedback! I sent messages to GD, my dealer, and Roadmaster Tire. I don't expect any quick replies due to the holiday - I'll start calling on Monday. 110psi seems to make the most sense.

[Grammy&Grandad]

Your setup is different than mine (I have the Dexter 8k axles with the 215/75R17.5 Cooper H Roadmasters and my GVWR is 18,000), but for what it’s worth, my sticker specifies 125 psi cold and that is what we are running. No problems so far. TST TPMS tells me that Solitude tires are all running right at 140 psi when warmed up. All good, and rides very well.

[orbsah]

To make a long story short, the GD rep in our area advised on the direction of the production manager that I should be running 120psi since that's probably what the rims are good for. Where do I find the rim pressure rating? Do I need to remove the wheel and look at the back side? Thanks!

[USA in a Chevrolet]

There is no need to run 125 psi unless your tires are carrying the maximum of 4805 lbs per tire. Use the Cooper Roadmaster tire inflation chart to determine how high your pressure should be. To determine your axle weights go to a Cat scale & weigh each axle. As an example my 345 GK front axle is 6420lbs & rear axle is 6340lbs. If each tire on the axle is carrying the same amount of weight the tires on my front axle are each carrying 3210lbs. Using the chart I only need to run 75 psi. I want an extra safety margin so I’m running 90 psi. I’ve attempted to attach the chart but if it’s not there you can google the chart for Roadmaster 170 M tires. The tire is listed as a pickup & delivery tire and trailer tire. If the attachment did not load I would appreciate a quick tutorial on attachments to posts. Overinflating your tires makes the trailer bounce a lot more & potentially wears the center of the tire quicker.