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Old 05-05-2013, 05:27 PM   #1
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Tire pressure conundrum

Regarding a new-to-us 1993 HR Imperial 36 DSP...

The placard specifies size 8R19.5, GAWR 6340 front and 13500 rear (duals). It also says 70psi front and 65psi rear. (??)

Stickers over the wheel wells say to use the pressure on the tire sidewall; for the ancient Michelins that was 90psi.

For our new Toyos the tire guy says to use 95psi. The dealer handles lots of truck tires so I believe they have a clue. However, according to the Toyo chart 95psi is proper for the fronts and the rears would take 105psi. Also the rims don't have any max pressure inscribed.

I know getting weighed is the thing to do but a scale is a ways away and it's not really feasible to go there yet.

So....suggestions? Thanks.
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Old 05-05-2013, 05:29 PM   #2
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For lack of any better information inflate to the maximum listed on the side walls. Duals usually have a lower number than singles BTW.
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Old 05-05-2013, 07:44 PM   #3
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That is just not right to inflate a tire to the max pressure on the sidewall. So what if the tire only requires 70 psi and the max is 125 psi on the sidewall. You would have a rough riding mh plus wear out the tire center plus have less traction in the rain because you are just riding on the center plus the mh is going to be real sensitive to steering and will be jittery. With your mh full of fuel, propane and water go to the closest truck stop with scales and weigh it so you have total weight on the front axle and total weight on the rear axle then look at Toyo's Load/inflation table for those tires which you can get from the dealer that sold you the tires, or search the Internet or somebody here can give it to you. Compute out the weight on each tire and look on the table and add 5% and that is your cold inflation first thing in the morning before you drive it
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Old 05-05-2013, 08:14 PM   #4
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Old 05-05-2013, 08:59 PM   #5
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According to the Toyo pressure chart, 95 in the fronts will carry the max rated axle load. 110, the max for that tire, in the rears will fall 300 lbs short of the max axle rating. The chart that I used was found at: RV Tire Care | Toyo Tires
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Old 05-05-2013, 11:11 PM   #6
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Quote:
Originally Posted by Mike Canter View Post
That is just not right to inflate a tire to the max pressure on the sidewall. So what if the tire only requires 70 psi and the max is 125 psi on the sidewall. You would have a rough riding mh plus wear out the tire center plus have less traction in the rain because you are just riding on the center plus the mh is going to be real sensitive to steering and will be jittery. With your mh full of fuel, propane and water go to the closest truck stop with scales and weigh it so you have total weight on the front axle and total weight on the rear axle then look at Toyo's Load/inflation table for those tires which you can get from the dealer that sold you the tires, or search the Internet or somebody here can give it to you. Compute out the weight on each tire and look on the table and add 5% and that is your cold inflation first thing in the morning before you drive it
The problem is not being able to weigh each tire, or dual set, individually. there is no way to know what the weight distribution is across the axle. If one side is considerably higher in weight than the other side, then one side will be under-inflated and the other side overinflated.

It then becomes necessary to inflate to the sidewall pressure for max load until it can be determined what the actual load for each tire is. In my opinion I consider this the "safe rule."

One can also use the "Chalk line" method to determine under inflation or over inflation. In a parking lot, draw a chalk line across the tread of the tire. Drive the vehicle several feet and then check the chalk line. If the center of the line is worn the tire is over inflated, if the outer edges of the chalk line are worn, the tire is under inflated.

Never exceed the sidewall max load pressure, and always check when the tires are cold.
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Old 05-05-2013, 11:17 PM   #7
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Most motorhomes are designed do that they are pretty close to equal weight from one side to another so that by increasing the load/inflation table recommendation by 5% it should cover far more accurately than what the OP has now. I do realize that the best way is to weigh each corner but that is sometimes hard to get done if not impossible.
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Old 05-06-2013, 09:14 PM   #8
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Thanks guys. Look like the best thing to do is to run 95/front and 110/rear until I can get it weighed. In our old class C we were several thousand pounds under max weight so I think we'll be ok.
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