Tires: rv tire difference, tire difference, rim width

Question
i have a 1976 argosy p-30 made by airstream the question i have is concerning the tires . currently on it now is the 8r-19.5 should i put those back on it or can i go with the 225/70/19.5? what would be the best tire for a comfortable ride and pulling a 25 foot boat? any help would be appreciated also if you could recommend a tire dealer that sells the tire very affordable? thanks for any info .

Answer
Billy,

First you need to find out what load range (or ply rating) the old tires are.  (There might be a placard that will indicate what the original tires were and what pressure to use.)

An 8R19.5 Load Range E (10 ply rating) carries 3195# at 95 psi.  The allowable rim width is 6.25" to 6.75" with a section width of 8.0" and a diameter of 33.8"

A 225/70R225 Load Range F (12 ply rating) carries 3640# at 95 psi.  The allowable rim width is 6" to 6.75" with a section width of 8.9" and a diameter of 31.9"

This means :

1)  If the current rims are 5.25" you can not do this change.

2)  If there is currently less than 1½" side clearance between the tire and the body in the worst condition (suspension fully turned AND fully compressed), you can not do this.

3)  If there is current less than 2" vertical clearance between the tire and the vehicle in the worst condition (suspension fully turned AND fully compressed), than you can not do this.

4)  If lowering the ride height of the vehicle 1" causes a problem, you can not do this.

However, if all these things work out, you can use 10 psi less pressure and get the same load carrying capacity - and that ought to improve the ride.

BTW, ride quality is more related to inflation pressure than differences in tires.  Put another way, different brands has only a minor effect on ride quality.

Also, these are honest to goodness truck tires, and you'll not likely find regular tire stores capable of handling these.  Call around to find out who will service these types of tires, particularly guys doing truck and commercial tires.  These are not inexpensive tires and you are not a buyer that buys in large quantity (like a truck fleet), so don't expect to get much of a bargain.