Wheel size and towing?

jmtandem wrote:

What are the thoughts on the effect of wheel size on towing, payload capacity, and gas mileage? Take the Ford F250 and F350 for example.

The XL and XLT models come with 17" wheels standard
The Lariat and King Ranch come with 18" wheels standard
The Platinum comes with 20" wheels standard.

After a bit of googling I have discovered that tires for 20" rims are significantly more expensive than for the smaller rims. But I haven't found a clear answer on which size wheels are most ideal for trailering and 5th wheels. Or for that matter, which are most efficient in terms of gas mileage.

If one is buying the truck primarily to haul a 5th wheel, is there any particular reason to prefer one wheel size over the other? Inquiring minds would like to know.

It also depends on the axle ratios. If the ratio is compensated for the 20 inch wheels and would be essentially the same as the 17 inch wheels with its ratio the towing differences should be moot. There may be slight differences in handling depending on the aspect ratio of the tire in corners but for most travel trailer and fifth wheel folks that differenece is probably not a priority. If the axle ratio and engines/transmissions are the same then the larger the tire the less rpm's per mile, less rpm's at any given traveling speed and less effective power. But, all that is blurred with transmissions and the ability to use gears to compensate. Some like 19 inch tires to With modern diesels it is hard to think that anybody would run out of power so get the wheels/tires you like and enjoy the trip.

I understand that one can replicate more or less the same outside tire diameter by using higher or lower profile tires. My question is more along the lines of which is preferred for payload and towing? Higher profile tires with smaller rims or lower profile tires with larger rims? And is there a preferred rim size that will make it easiest to find replacement tires on the road should I experience a blown tire in some backwater town? I'd hate to be stuck in the middle of nowhere and find out "sorry...we can't help you, you should have gotten the 18" rims"