The 18" rims should be able to support a heavy duty tire, while the 20" 'Bling' rims are not real truck tires, and nobody makes a LT Light Truck tire for them.
If you look at the 1930's style model A tires, they are like motorcycle tires, with very little distance between the road and rim, leaving a very bumpy ride. Also check those 20" 'Bling' tires, they have very little space between the road and rim, so a deep pothole can cause the rim to pinch the tire rubber, and blow out the tire nearly instantly! Also the tire does not have 3" of rubber to eliminate vibration and road bumps nearly as well as say a 235/85R16" rim with 5" of rubber between the road and rim!
I have a friend with a 1970's Charger, and it can take the speed bumps! At say 35 MPH and just float over the speed bumps! Much better than a pickup, or anything else with stiff suspensions. This is in part due to the 'balloon' tires, and their ability to absorb the shock, and not transmit much of it to the car.
I would be looking for a truck without the bling. Tell the dealership that you would buy the (pick your color) but it comes with 20" rims that are not acceptable, and you are going to the other dealership to check truck selection. I am sure that the service department can change 'this truck's 20" rims to that truck's 18" light truck rims in a few minutes, if you wanted that truck. Make sure that they also take that 'extra price' off the list price of the truck you buy. ..
Also if you will be looking at fifth wheels in the next few years, you probably will not want to replace your 2500 pickup with a 3500 pickup then. So check out a few fifth wheels now, and pick up a brochure. Pick the pickup with enough cargo rating to handle 'your' fifth wheel this year, or you might not be able to buy that fifth wheel in a few years, due to needing to upgrade trucks at the same time!
Most 12,000 pound fifth wheels will have a 2,400 pound pin weight, give or take 600 pounds! So a 2500 pickup with a 2,800 pound cargo rating will not do. Of that 2,800 pound rating, you must subtract all the passengers, 100 pounds - 150 pounds for the fifth wheel hitch, and still have 2,400 pounds left to carry the pin weight. That just will not add up.
Check the weight rating of a 3500 pickup too. You should see it rated at around 1,000 pounds more than a 2500 pickup, even if it costs $865 more! But it will save replacing it in a few years, saving thousands!
Good luck,
Fred.
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Porsche or Country Coach!
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