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My trailer tires are labelled only with the following:

  • Carlisle made in USA

  • 6.90-9

That's it - there is no max PSI, # of plies, load rating, or any other information at all that I can see.

The actual pressure is ~33 PSI and ~35 PSI and they both seem to hold air fine. (I don't know if these values are meaningful, the last person to inflate them might have guessed.)

The rims are in two halves (inside & outside) which are bolted together. I think therefore this means the tires have inner tubes, if that makes any difference. I don't know if it has any bearing on inflation pressure.

Is there any way to determine what a proper & safe operating pressure would be?

Given the lack of markings, could these not be meant for road use? Or just really old? (Their condition seems OK, FWIW).

Edit: Photo of tread pattern, in case that helps with identification.

enter image description here

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  • This sounds like a daft question, but do they have valves? Could they be solid tires? Often the case with smaller split rim wheels & tires...
    – Solar Mike
    Commented May 17, 2019 at 22:13
  • @SolarMike - These would be air ride tires, but good thought. The size mentioned is a standard trailer tire size here in the States and Carlisle makes a good many of them. To the OP, do one of the treads look familiar on this Carlisle page? On the "Trail" tires, the only 6.90-9 tire is set at 60psi.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented May 17, 2019 at 22:36
  • @SolarMike yes, there are valves.
    – StayOnTarget
    Commented May 18, 2019 at 1:31
  • @Pᴀᴜʟsᴛᴇʀ2 Thanks for the suggestion. I've compared to that page (and added a photo here), none are an exact match. "USA Trail" is the most similar. I looked through their PDF catalog too, still no match that I could see.
    – StayOnTarget
    Commented May 18, 2019 at 19:45

1 Answer 1

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The solution turned out to be: ask the manufacturer.

For my specific tires the details are pasted below. This itself may not help many other people unless you have the exact same tire. But the general approach of checking with the maker seems to be pretty sound. This had the added benefit of discovering the tire load rating, max speed, etc. all of which is valuable information.

Details for my specific tires are as follows:

Inflation and Load Data:

  • Rated Speed 62 mph 99.8 km/h

  • Rated Pressure 60 psi 414 kPa

  • Rated Load 1100 lbs 499 kg

They also included the following other info:

  • Inventory Code 519572

  • Size 6.90-9

  • Tread Pattern USA Trail

  • Load Range LRC

  • Load Index 84

  • Speed Symbol J

Original PDF from Carlisle:

(Including the PDF just for authenticity, but the text above is more searchable)

enter image description here

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  • Usually, the "rated pressure" is not the pressure you want. The pressure you want is a complex combination of tire size, trailer weight, etc. The rated pressure is just the pressure you can never exceed.
    – juhist
    Commented Jun 27, 2019 at 18:37
  • I'd check with the trailer's manufacturer to see if they have tire pressure recommendations, or a table that correlates tire pressure to the weight of the load.
    – smitelli
    Commented Jul 23, 2019 at 14:13
  • @smitelli thanks, that's a good suggestion. In this case the trailer is homemade but the axle appears to be at least 3500 lbs based on the spindle diameter. So the tires could in fact be the limiting factor, but I don't think there would be an even lower max load.
    – StayOnTarget
    Commented Jul 23, 2019 at 14:37

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