# tire pressures again??



## wilf (Oct 2, 2009)

i just found the tag behind the drivers seat for tire pressures on my mh  it says front 5300   8r 19.5 d 65 psi cold, the same for the rears althought the gvr states 10,000 for the rear 

when i weighed the rv it was  4700 front and 7780 rear the tire itself says max load 3300 and 110 psi there is 95 psi in them all right now  anyone know why the tag says 65 psi and the tire says 110 psi thats a big difference ? 
also the actual tire says its 8r 19.5 F  the tag says tires 8r 19.5 D whats the difference between F and D ?

 its pretty confusing its my first MH and i am going on my first long trip this weekend, (well a few hundred miles) and i am concerned about having the correct pressures anyone help??


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## Triple E (Oct 3, 2009)

RE: tire pressures again??

Are these the same tires that were on your MH when it was new?  Just to be safe, take you rig to your nearest tire dealer and have them explain what all of those letters mean and what the best tire pressure is.  My tire shop recommends 100 psig.  Have a safe trip.


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## wilf (Oct 3, 2009)

RE: tire pressures again??

the tire shop said 95 the next time they said they usually put in 10 psi less than the tire says which would be 100 psi but the door tag says 65 psi ? the motorhome is a 93 model the tires on the front are 3 yrs old and 5yrs on the rear ?


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## brodavid (Oct 3, 2009)

Re: tire pressures again??

need to get ready to change out your tires getting old. mostly the rear


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## Kirk (Oct 3, 2009)

Re: tire pressures again??

What make are the tires? The manufacturer of the tires should provide an inflation table that will give the proper inflation for the tires based upon the weight that is riding on them. The proper pressure is to use the one from the chart, plus 10%. If your tires are from either Goodyear or Michelin, both of them have inflation tables for their tires on their internet site and they can be down-loaded. You should never put different air pressures in two tires on the same axle, so you take the weight of the higher loaded tire and use it in both tires. If you only have weights by axle, I would assume that the weight is split at 40% one side and 60% on the other when selecting the proper inflation pressure, just for safety. Very few RVs are properly balanced from side to side.

As to what it says on the sticker, remember that the sticker was made up in 1993, when there were different tires for sale than there are today. The information should have been based upon max. loading of the tires that came on the RV.  

The F and the D are load ranges that are set by a federal highway standard. A load range F tire is to ratings higher than one of D. That is no doubt part of the difference in inflation numbers. As you increase the carrying capacity of any tire the air pressure in it has to increase. Remember that if you have 2000# of weight on a specific tire, then that 2000# must be distributed over the number of square inches of tire that touch the road. In other words, if you had ten square inches of tire carrying that 2000# it would require at least 200# of air pressure to carry it. 

Since your RV tires are probably around 6" or so wide and probably close to 6" of length are on the ground, that means that you have 36 square inches of tire to carry the load. It would thus mean that the tire could lift 3600# of weight if inflated to 100#/sq. inch. The tire ratings usually are designed to be significantly above the minimum inflation to life the rated weight, but have to be at least that much. As you go up in load rating, the tires are of heavier construction and are designed to be inflated above the minimum for design reasons but different newly constructed tires hve different load ratings and each has it's own ideal inflation pressure. 

You must base it upon the make and model of tire that you have, as well as it's load range.


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## DL Rupper (Oct 3, 2009)

Re: tire pressures again??

To cut to the chase, use the psi that's on the tire sidewall until you get to a reputable tire dealer that can check the tires out.  

Your tires are good for 7 years of wear and tear.  If you keep tires on longer, regardless of the tread depth and looks of the tires, you are asking for blowouts.  The sun (UV) and weather wear the side walls of the tires out.


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