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 > Tire Pressures

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dnix@ra.rockwell

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Posted: 05/25/02 12:46pm Link  |  Print  |  Notify Moderator

OK, I have a 9 ton MH on a P30 chassis. The tires are Goodyear G159 Unisteel, 8R19.5’s. The tire states that maximum pressure should be no greater than 110 psi but recommends no low limit. What are those of you with similar setups running? And are you running different pressures front to back?


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Norm Payne

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Posted: 05/25/02 01:41pm Link  |  Print  |  Notify Moderator

The tires have different rating whether mounted single (front axle) or dual (rear axle). There is only one way to know how much pressure to run on each axle. With your motorhome loaded the way you travel, fluids, people and stuff aboard, weigh each axle. Then use a Goodyear tire inflation guide and adjust the pressures according to what Goodyear recommends.


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dsouthw524

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Posted: 05/26/02 06:24am Link  |  Print  |  Notify Moderator

The only thing that was missing on the previous answer was - get the coach weighed! No one can tell you what pressure to put in accurately until you have at least the front wheel weight and back axel load. Then the tables will tell you what air pressure you need.


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Dale3

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Posted: 05/26/02 08:29am Link  |  Print  |  Notify Moderator

I was under the impression that the max. inflation pressure listed on these tires IS the minimum to carry the specified load. I've read many previous posts on this forum, and articles in both Highways and Motorhome magazines that state for safety purposes, until you have the axle weights, the best bet is to inflate 10 pounds over the PSI stated on the tires. Have I misinterpreted??


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hwybnb

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Posted: 05/26/02 12:15pm Link  |  Print  |  Notify Moderator

As many times that this topic has been discussed here I am amazed that there is still so much confusion and misinformation on it. Here it is once again:

The only correct way to determine proper inflation pressures is to (1) weigh the rig and (2) consult the tire manufacturers load/ pressure charts to find the right value. The correct pressures will normally be different front vs. rear. When weighing you should as a minimum get seperate weights for each axle. Seperate weights for each wheel or wheel pair is better.

Until you get the weighing done inflate to the maximum pressure marked on the sidewall. That is just what is says it is. It is the maximum, not minimum, and must be measured when the tires are cold. The other interium option is to go by the pressures recommended by the coach manufacturer, if available.

Some "experts" advise inflating to 10 psi over the chart value as a safety margin. I don't buy that argument because the recommended inflation pressures already include a safety margin and going beyond that is over-inflation.


R2

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Posted: 05/26/02 12:22pm Link  |  Print  |  Notify Moderator

M. Dean Nix

I have the same tyres and wrote Goodyear for their load chart. Here is their reply and the chart they sent me.

I would suspect that you have load range F 245/70R19.5 tires on your vehicle, while the 265/70R19.5 is a load range G size. The difference is close to 1000 lb extra carrying capacity per tire, which would explain the discrepancy in inflation pressures between these two dimensionally similar tires.

You can definitely run your tires at an inflation pressure less than 85 psi if you are not loaded to the maximum capacity. You can use the chart
below to determine your optimum inflation pressure. We do not recommend going below 70 psi with this tire, however.



|----------+--------+--------+--------+--------+--------+--------+--------|
> |psi |70 |75 |80 |85 |90 |95 |100
|
>
|----------+--------+--------+--------+--------+--------+--------+--------|
> |dual load |3415 |3515 |3655 |3875(F) |3940 |4075 |4375(G)
|
> |lbs | | | | | | |
|
>
|----------+--------+--------+--------+--------+--------+--------+--------|
> |single |3640 |3740 |3890 |4080(F) |4190 |4335 |4545(G)
|
> |load lbs | | | | | | |
|
>
|----------+--------+--------+--------+--------+--------+--------+--------|
>
>
>
We suggest having your loaded RV weighed at a location with the capability to determine the actual max loading on each axle position. Then inflate all tires on that axle to the inflation pressure needed for that max loading. Many recreational vehicles are designed with a weight
bias front-back or side-to-side that may put unequal loading on one or more tires.

Please feel free to contact me with any additional questions you may
have.

Regards,
Janice Consolacion
Product Manager, Commercial Tires
The Goodyear Tire & Rubber Company
---------------------- Forwarded by Janice Consolacion/NA/GDYR on


*This Message was edited on 26-May-02 12:25 PM by R2*



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Pirate

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Posted: 05/26/02 09:30pm Link  |  Print  |  Notify Moderator

Amen. And don't trust your local mechanic or the place where you bought tires. Use the tire charts from the manufacturer.

WinneChief

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Posted: 05/27/02 10:11pm Link  |  Print  |  Notify Moderator

Ah, Dave, but the PSI indicated on the sidewall of truck/RV tires IS the MINIMUM inflation pressure to carry the MAXIMUM load on that tire.

If you do not carry the maximum rated load on the tire, you may reduce the pressure according to the manufacturer's tables, which also indicate a minimum pressure required to carry a given load. Still confused, Dean?


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