Correct Tire Pressure?

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From: Tony_In_Lake_Elsinore (Original Message)
Sent: 4/24/2005 10:09 AM

Hello all,

I have a '74 Brave.  Still have to post pictures...  She's an awesome beast.

My tires are at 59.5 psi.  I know, that's really low (she's been sittin' all winter).  The printing on the sides says they should be at 85 psi at max load.  That seems high.  Recommendations?




From: denison Sent: 4/24/2005 8:10 PM
It would be safe to run them at the max pressure figure, or probably within 10% to 15% below it, depending on how close to the tires maximum load rating your RV adds up to.
The sidewalls on mine say a max of 90 psi cold, when running as a single (on the front axle): And a max of 80 psi cold when running as dual tires on the rear axle. I run 75 psi front and 70 in the back.
I also check my tire temperatures Every time we stop on our vacation drive, at rest areas, service stations, eateries, etc. I want the tires to all be equally warm.
Did Lake Elsinore overflow its shores after all the rains? 




From: cooneytunes Sent: 4/24/2005 11:24 PM
Tony,
You can go to the max cold inflation....I have 8R x 19.5  12 ply with an F raring tires on my rig. The max cold pressure is 110psi.....I run 95psi in the fronts....and 90psi in the duals....seems to do OK...I can't run too much more due to my rims are rated at 100 psi max cold... Also weigh your rig. Toal weight and per axel. Loaded with all stuff you take with you on a trip, and tanks full, ie: water, LP, and fuel....This will let you know if you are exceeding the GVAW....also not overloading the tires... Also, if you run too under inflated the tires will heat up extremly fast, and that could be dangerous at 60 mph on the highway.
Hope this helps...
Timmy
   
 


From: ClydesdaleKevinSent: 4/24/2005 11:35 PM
I haven't even checked my tire pressure yet.  Tire pressures are THAT HIGH?  I'm used to high pressure in bicycle tires, but on the RV?

My Ford F-150 takes about 35 psi.  Are you saying that my RV tires should be 75psi in the front, and 70psi in the back?  Just checking so I make sure I have the right pressures for the trip.

Kev

   

From: OldEdBrady Sent: 4/25/2005 1:04 AM
My tires--which are old and in need of replacement--call for 80 psi.  They're 17.5s
 







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From: cooneytunes Sent: 4/26/2005 12:50 AM
What size are your tires?   

From: <NOBR>DaveVa78Chieftain</NOBR> Sent: 4/26/2005 2:40 PM

As you can see from the different responses, there are different values for tire pressures.  The tire chart above is for the bias-ply tires that originally came on these rigs.  Each tire mfg has their own set (single/dual) inflation charts therefore you should use the ones from the mfg of the tires you have installed.   In many cases though, they may no longer be available.  In that case you are left with using a best guess based on the information printed on the tire.  You can build a tire pressure chart that should closely fit yours by bassing it on percentages of the posted chart.  For example; The 8-17.5 (6-C) one has max single capacity of 2075 at 45 lbs air pressure.  At 40lbs air pressure it is rated at 1940 lbs which is 93% of max.  At 35 is 86% and 30 is 79%.  So if you have a tire that says max pressure of 80lbs at 2455 then 93% (75lbs pressure) of 2455 is 2283.  86% (70lbs) is 2111 and 79% (65lbs) is 1939.  While this is a ballpark is is better than nothing when the charts are no longer available for the tire you have.   Works the same for duals but you would use the computed values for a dual example.

Dave


 

From: cooneytunes Sent: 4/26/2005 8:18 PM
Dave, that's some great calculating...I could be wrong, but looking on the side of my new(radial) tires, the bias and radials that came off my rig fromPO (7 different brands, 5 different plys... 8 brands including my new ones)   ....the chart is from the 1977 Service Manual and is still pretty close, both in pressure and weight rating according to ply and letter rating.
The area in which the air fills is still the same, only the materials and componds around the air have change thus pressure and weight ratings are very very close if not the same...But, always get all the info you can from the manufaturer specific to your tires you'll be using...the chart is a good guide line.
Timmy