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Old 10-07-2011, 09:31 AM   #1
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Tire pressures

Continental tire-HSR225 70R 19.5 load range G. Tire is rated for 110psi cold inflation temp. From the IRV2forum back in July,2010 pairajays submitted a Universal Tire Pressure Chart. Per this chart I will be filling my tires at a temperature of 75ish degrees meaning I will inflate tires to 113psi per this chart. Puts me over the 110 rating. Is this an issue or is this a compensation for either rising/falling ambient temperatures thereby providing a safe range of operation/ Thanks for your comments.
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Old 10-07-2011, 09:53 AM   #2
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Use the tire pressure chart from Continental for that tire.
Per your 4 corner weight of your RV. Only way to know the PSI you should be using.

You probably will only need a lot less then the sidewall rating.
And will get a better ride for it.

No adjustment needed from Ambient temperatures. Just put in the PSI for your weight that Continental's chart says. Usually in the morning is the best time to do it.

Download this PDF from Continental and Page 28 has your PSI per weights

A Universal chart may not know what pressure your rims are rated for.
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Old 10-07-2011, 11:27 AM   #3
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Originally Posted by ToledoCharli View Post
Continental tire-HSR225 70R 19.5 load range G. Tire is rated for 110psi cold inflation temp. From the IRV2forum back in July,2010 pairajays submitted a Universal Tire Pressure Chart. Per this chart I will be filling my tires at a temperature of 75ish degrees meaning I will inflate tires to 113psi per this chart. Puts me over the 110 rating. Is this an issue or is this a compensation for either rising/falling ambient temperatures thereby providing a safe range of operation/ Thanks for your comments.
I apologize for posting that chart. I have since learned that is not the way to set your tire pressure. All the tire manufacturers publish a load inflation table for their tires. The correct pressure depends on the tire and load it is supporting. The pressure indicated in those tables is the minimum pressure when the tire is "cold". The key is "cold", just what is "cold? A tire is cold after it has rested for at least 2 or 3 hours and has reached ambient temperature. That means out of the direct sunlight.

So, your tire pressure should be set according to the manufacturer's load inflation tables when the tire is cold. As an RV'r, the most logical time to do that is first thing in the morning before getting under way. An example, if the load inflation table specifies your pressure should be 100 lbs and the ambient temperature is 65 degrees, then the pressure should be set to 100 lbs. Same is true if the ambient temperature is 80 degrees, tire pressure should be set to 100 lbs. So it does not matter what the actual ambient temperature is because that is "cold".

It seems most RV's add about 5 lbs more than required as a safety factor. So this attention to tire pressure detail seems to be a mute point. I, personally, don't think it makes a nickel's worth of difference what your pressure actually is as long as it is at or above the minimum as specified on the manufacturer's load inflation table and does not exceed the wheel spec. If someone is picky about ride comfort, then the lowest pressure allowed is probably the way to go. Personally, I have never been able to detect any difference in ride quality attributed to tire pressure.

That's my story and i'm sticking to it.

Jim E
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Old 10-09-2011, 07:52 AM   #4
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Excellent advice, Jim!
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Old 10-09-2011, 03:02 PM   #5
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Parajays - You said it was a "mute point". Did you mean "moot point"? Or maybe I should just be mute.
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Old 10-09-2011, 03:57 PM   #6
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I learned the hard way on running max tire pressure on my first RV. Too high a pressure was one of the two leading causes of throwing the thread off of the Bridgestone I had on a Toyato Dolphin. I've copied the pressure chart to file on the tires that are on my 37DB.
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Old 10-10-2011, 08:56 AM   #7
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Parajays - You said it was a "mute point". Did you mean "moot point"? Or maybe I should just be mute.
I flunked spelling in grade school.

Jim E
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Old 10-10-2011, 09:00 AM   #8
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Originally Posted by mustang652 View Post
I learned the hard way on running max tire pressure on my first RV. Too high a pressure was one of the two leading causes of throwing the thread off of the Bridgestone I had on a Toyato Dolphin. I've copied the pressure chart to file on the tires that are on my 37DB.
There is a max pressure on every tire. Did you exceed that? If not, it must have been a faulty tire.

Jim E
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Old 10-27-2011, 02:04 PM   #9
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Just a note about LT and truck tire pressures. Passenger car tires (prefixed with a P before the section width as in P235/etc) show the maximum pressure the tire can safely contain and how much weight that pressure can support. LT or truck tires show the minimum pressure required to support the maximum load a tire can support. This is from the Michelin truck tire PDF file on their web site.

While it is never adviseable to exceed the maximum weight rating of any tire, it is only P class tires that have a maximum pressure moulded into the sidewall. Truck tires will not support more than the stated maximum weight even with additional pressure but they may run a little cooler when carrying the weight limit.

The rim is usually well matched to the OEM tire by the chassis manufacturer so the lower of the rim or tire max pressure is the limit of the combination. Aftermarket tires already installed may be a higher load range than the rims so if yours is a used rig it is worthwhile examining the rims closely to read the load and pressure limits stamped on teh lip of the rims.

One other note. Running higher than needed presures reduce the ability of a tire to absorb road shocks and can result in tire damage including tread seperation and internal sidewall damage. In bias ply tires (does anyone stilll use these?) additional pressure may result in a smaller tread contact patch which may affect steering and braking especially in the wet.

Personally, I run 5psi over table values on the RV and 3 over factory recommendations on the Acura and GoldWing.

My .02 worth.
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Old 10-27-2011, 02:12 PM   #10
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Quote:
Originally Posted by Bobog View Post
Just a note about LT and truck tire pressures. Passenger car tires (prefixed with a P before the section width as in P235/etc) show the maximum pressure the tire can safely contain and how much weight that pressure can support. LT or truck tires show the minimum pressure required to support the maximum load a tire can support. This is from the Michelin truck tire PDF file on their web site.

While it is never adviseable to exceed the maximum weight rating of any tire, it is only P class tires that have a maximum pressure moulded into the sidewall. Truck tires will not support more than the stated maximum weight even with additional pressure but they may run a little cooler when carrying the weight limit.

The rim is usually well matched to the OEM tire by the chassis manufacturer so the lower of the rim or tire max pressure is the limit of the combination. Aftermarket tires already installed may be a higher load range than the rims so if yours is a used rig it is worthwhile examining the rims closely to read the load and pressure limits stamped on teh lip of the rims.

One other note. Running higher than needed presures reduce the ability of a tire to absorb road shocks and can result in tire damage including tread seperation and internal sidewall damage. In bias ply tires (does anyone stilll use these?) additional pressure may result in a smaller tread contact patch which may affect steering and braking especially in the wet.

Personally, I run 5psi over table values on the RV and 3 over factory recommendations on the Acura and GoldWing.

My .02 worth.
I have posted pretty much the same numerous times on this and other forums and there is always someone that argues the point and says I'm wrong When in fact it's in the tire manuals and I include the link to them!
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Old 10-28-2011, 07:37 PM   #11
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If you do not know the weight of the coach, either a 4 corner weight or front and rear axle weights, there is no way to establish the correct tire pressure.

If you do not know any of the above, then the only pressure to use is the max tire pressure which in your case is 110 pounds.
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