Tires: Motorhome tires, stock tire size, motorhome tires

Question
I have more details about my motorhome tires.  I own an 1988 Airstream 325, three axles, eight tires, GVW 16,500 lbs.  Stock tire size is 8R19.5 load range F.  The tire is rated to hold 3,500 lbs @ 110 psi.  The factory recommendation is to inflate to 70 psi.  I would like to use a wider tire.  The rim width is 6".  What wider tire size can I upgrade to and get a load range F tire?  Thanks

Answer
Glen,

A 225/70R19.5 will fit (barely) on a 6" wheel.  It's 8.90" wide - 0.90" wider than what you have now.  However, it is smaller in diameter - 31.93 vs 33.82 - so it will lower the trailer about an inch.  And you will need to check your clearance.  Don't forget about suspension travel and the fact the tires flex, especially when going around corners.

What you should be interested in is load carrying capacity - not load range.

At 70 psi the 8R19.5 only needed to be a D load range, and carried 2540 #.  A 225/70R19.5 only needs 58 psi to carry that load, again a load range D, however, I would recommend you use 65 psi as a minimum, which gives you a capacity of 2755#.  

BTW I would recommend you have the vehicle weighed axle by axle, and if poosible wheel position by wheel position.  Load it up for the worst case - everything you think you could possibly put in it, graywater, black water, completely full.  Trailerl manufacturers are known for putting the smallest possible tire on, sometimes too small - although this doesn't appear to be the case here.

Knowing the weights involved will help you know what the worse case is and that you will never overload the tires.  I'd also recommend a minimum of 10% reserve capacity (15% would be better).  Reserve capacity is unused capacity.  So if the tire is carrying 1000#, inflate it to carry 1150 #.  If you need help determining what the inflation pressure should be, I'd be glad to answer that question, once I know the weights involved.

One last thought:  You'll need to check your dual spacing.  The 225/70R19.5's require a 10" minimum (centerline to centerline.  Your 8R19.5's only required 9.1"  If the duals touch under load, the carcass gets distorted and all kinds of strange failures can happen.

Hope this helps.