4aSong
Northwest Arizona
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Joined: 10/15/2003
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I recently replace my Goodyear Marathons (4 ply) which had a MAX pressure of 35psi with a different brand (8 ply) that have a MAX pressure of 60psi. Question, will the rim withstand the additional pressure and how can I check this ?
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BurbMan
Long Island, NY
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Joined: 09/20/2001
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Ahhhh, the million dollar question. You no doubt missed the many other tire threads that discussed this. You should check the load and psi rating on your wheels before you go to a heavier tire because the wheels may not be rated for that pressure or load.
There will be a load rating stamped on the wheel. Sometimes it's on the back, and sometimes it's inside the rim so the tire has to be dismounted to see it.
8-ply tires are load range D that have a max capacity of 2540 lbs at 65 psi. Wheels that will handle D-rated tires are typically rated at 2600 lbs. I would definitely check the ratings before you air those tires up all the way.
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kamper00
Meriden, CT
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Joined: 05/24/2004
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I have always wondered what the relationship between the psi and the rim? I know mine are stamped for 50psi and have considered going up a load range which require 65psi....my only thinking would be the bead???
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BurbMan
Long Island, NY
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The rim is only tested to hold the rated psi. More than that and it could bend the bead, separate if it's two piece rim, etc. Sadly, you won't know what the weak point is until it blows up.
Not saying that 51 psi makes it blow off the trailer, but you would be past the safe design specs of the rim.
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Kenneth
Washington, the state
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Just some clarification...
"Standard Load" tires may have the max inflation pressure of 35 psi (some are 44 or 51 psi). They probably have one or two plies of polyester cord. Fifty or sixty or more years ago they would have had four plies of cotton cord.
Load Range D tires carry their max load at a minumum inflation pressure of 65 psi, and need 10 psi more to carry the max load at speeds above 65 mph to 75. Above 75 they need the additional 10 psi plus a reduction of load. Half a century ago tires like this would have needed eight plies of cotton cord. These will have two or three plies of polyester cord.
Many wheels have no rating stamped on them. Make conservative assumptions about what they can carry. There is no need to inflate a higher than original Load Range tire to its max if less pressure will carry the load.
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JJBIRISH
Butler, PA, USA
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Kenneth
I am not sure I agree with you I of speed variation...
if you are using the loading charts for ST tires you have a speed rating of 65 MPH, if you need to go 70 MPH you can raise the PSI by 10 providing it doesn't exceed the maximum PSI for the tire or the rim... if you feel it is necessary to go up to 75 you can decrease the load by 10%, but at no time should those increases exceed the maximum ratings for load OR PSI...
that is my understanding any way from memory, as I haven't read it in a very long time...
the same rules apply for LT tires in trailer use except it is + 10 PSI to go up to 75 and no reduction in load... again maximum psi doesn't change for the tire or the rim... the load has to be sufficiently low to add the extra air based on weighing and the load charts...
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tvman44
Southwest Louisiana
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More than likey not, the manufacturers seldom use anything rated higher than necessary.
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4aSong
Northwest Arizona
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Well now that you all have me worrying, I have decided to take one of the tires back to the dealer to have them remove the tire from the rim and see if there are any marking on the inside of the rim as to the maximum PSI the rim is rated for as there are no markings on the outside of the rim.
Just curious, what if they cannot find any PSI rating ?  How much trouble is it to find replacement rims ?
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Cool Canuck
Winnipeg, MB, Canada
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Joined: 08/18/2003
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Most trailer rims are made by Carlisle. There use to be a sheet with the rims and their max psi, however, I can no longer find it. Here are a couple of sheets which show their max load ratings.
Carlisle Wheel Cat
Trailer Reference
You can use tires that have a higher capacity. Just use the air pressure for the original tire and keep the load down to that. In other words, you can use a Load Range E tire to replace a Load Range D but only air the tire to 65 psi instead of 80 psi and keep the load to the capacity of the "D" Range tire.
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4aSong
Northwest Arizona
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As Cool Canuck mentioned “You can use tires that have a higher capacity. Just use the air pressure for the original tire and keep the load down to that. In other words, you can use a Load Range E tire to replace a Load Range D but only air the tire to 65 psi instead of 80 psi and keep the load to the capacity of the "D" Range tire.”
If I understand Cool Canuck correctly, we should keep the air at 35psi instead of 65 and maintain the load capacity of a “B” rated tire. A few additional questions:
1. Will there be a problem with the tire overheating?
2. Could there uneven tire wear?
3. Excess deflection?
4. Will this weaken the tire structure?
Our trailer is a 19’ Prowler lite with tandem axels, the dry weight is 3300 Lbs and loaded it is rated at 4400Lbs.
The Original tires were Goodyear Marathon ST205/75R14 4 ply load range B (max 35psi) Made in USA.
I recently replaced the tires with Westlake H160 185R14C 8 ply load range D (Max 65psi) Made in China.
The following information was found on the Internet:
Disadvantages of Underinflation
An under inflated tire can't maintain its shape and becomes flatter than intended while in contact with the road. If a vehicle's tires are under inflated by only 6 psi it could weaken the tire's internal structure and eventually lead to tire failure. Lower inflation pressures will allow more deflection as the tire rolls. This will build up more internal heat, increase rolling resistance (causing a reduction in fuel economy of up to 5%) and reduce the tire's tread life by as much as 25% while increasing the probability of irregular tread wear. Drivers would also find a noteworthy loss of steering precision and cornering stability. While 6 psi doesn't seem excessively low, it typically represents about 20% of a passenger car tire's recommended pressure.
Based on the above information, if we keep the air at 35psi instead of 65 and maintain the load capacity of a “B” rated tire. Will we encounter:
1. Tire overheating?
2. Uneven tire wear?
3. Excess deflection?
4. Will this weaken the tire structure?
5. Other concerns I may have overlooked?
Appreciate all the information provided.
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