I would suspect ( my disclaimer) that since the 20" tires have 110lbs higher load rating than the 18" wheels, that if you let a little air out and run slightly softer, basically at the same load capacity as the 18" tires, the difference in the sidewall won't be that noticeable. i.e the 275/70r18 at 80psi = 3640 lbs vs the 275/65r20 @ 80 psi= 3750 lbs

But yes at the exact same pressure, the larger sidewall would give slightly better flex.

I have the 20" and have driven a lot of washboard BLM and Forest Service roads in Utah and Wyoming and don't consider it a bad ride. It's a truck and I usually have 13,000lbs of GN horse trailer behind me.

 

The 18's can lead you to think that they ride smoother but the same smoothness can probably be had with tire pressure experiments.

Maybe drive both?

I think the 18 May ride smoother and perform better with heavy weight on them but not so much as to convince me to get them. I fell victim to thinking the 20" wheel styles look better and the 20" look on the truck is nicer, vein I know. If ford had an 18" wheel that looks just like the 20" wheel style/design I'd be a lot more interested in them. Makes me feel stupid but it's the honest truth.

 

The ride is going to suck just as much on 20s vs 18s in those road conditions.

 

The blue one has 20's, the red truck has 18's. I drive both, tow with both, no noticeable difference..... Actually the red one is more fun drive, but that has to do with the lost of some unnecessary weight, not tire size

 

Those wheels make may sixteens look really small. Man, I can hardly wait to get my new truck. Going with the twenties all the way.

 

As Painted Horse pointed out the 20's have a higher carrying capacity. A few other things to consider, 20's cost a little more ($40 ea), 20's will cover a mile in 610 revolutions, where as 18's = 627. 20's diameter is 0.8 inch more. I hope this helps you out. JG

 

I have 20" on my truck and have been very pleased with the ride on our crappy Vermont roads, dirt and paved (paved is charitable - mostly potholed with asphalt between the holes). My reasoning for the 20's was I tow an 18,000 lb toy hauler in my sig. I was looking for a shorter sidewall and less flex and I thought the 20 would give me that. That said, I'm in the market for a set of take off 18" to mount snow tires on. Twenty inch snows are hard to come by - not a lot of choices. If you go to 18" the options open way up and are cheaper.

Best way to improve the ride is found in replacing the stock shocks with Bilstein or real Ranchos. The stockers are crap (IMHO).

Good luck with your decision. Lots of good advice here.

 

I went from 20 to 24 and didn't notice any difference in ride. Properly inflated the tires don't flex much at all anyway unless you hit a huge bump. Underinflated tires flex and then they get hot and blow. Suspension is what dictates the ride. Springs and shocks. You can't even feel the minimal flex in that small of a difference. You might feel it a little with 15 inch rims running 35s vs 28s with low profile tires, but from 18 to 20s you might gain about 1/16th of an inch more rubber flex, lol

 

I ordered mine with 18's because of replacement tire cost. I like the way the 20's look, but unless you put them side by side it is hard for me to tell the difference.

 

when I bought my truck it had the ugly a$$ chrome plated plstic 18" wheels and continental tires. I hated them enough to buy different wheels. I ended up with a set of used 20" wheels from a super duty platinum. put on a set of firestone destiantion a/t tires and it looks and handles awesome. the truck is black and with the black inset in the aluminum wheel it got rid of just enough of the shiny stuff to look great. the tires are dead quiet on the highway and have a nice aggressive tread. the speedo changed though. now instead of going slower than the speedo says, you are going a little faster than the speedo reads (gps). the mpg changed on the dash, but that is a result mostly of the odometer no longer being accurate. actual mpg is not noticeably different. I'm going to use the old wheels for dedicated snow tires next winter (unless I sell them first).

 

I'm like a pendulum swinging backwards and forewords with my decision on if I should get the 18" or the 20" on my new F350 SRW.

After spending most of last week on the 18" side I spike to a guy this weekend who convinced me to go 20"

From one I'm getting, it seems that there is actually very little difference in the two.

- With 20" we are NOT talking Low Pro tires.. in fact the fall is only about 0.5" shorter

- Width is the same

I have until Wednesday at the latest to make up my mind and place the order for the truck. (I have a time constraint)

If I went 20" would anyone shout NO DON'T DO IT!!!!!

 

Have driven the same truck 20,000 miles before and 4000 after switch to 20. Didn't notice any ride difference. No one ever said anything about wheels before. After installing 20 inch wheels I have gotten compliments on how nice the wheels look

 

I've been asking this question all over the place. The conclusion that I'm coming to is that THEORETICALLY the 18" has more side wall so should give a sorter ride.

However I'm coming to the conclusion that this increase in sidewall is so little that it in really won't feel any different.

The differences being:
- 20" are $50 each more
- 20" looks better

 

If you go with 20's and it sounds like you are, I like the 20" Premium Cast Aluminum Wheels for just a little more $$$ than the 20" Chrome Clad Aluminum Wheels. The 20" Chrome Clad Aluminum Wheels have a fancy plastic coating. It's not much more for the Cast Aluminum Wheels.

 

It doesn't matter. You'll be fine with both. You have a wider choice of tires and sizes for an 18" wheel, and they're cheaper per tire as well. But it's mostly a question of aesthetics.

PS People, a 20" wheel has 2" more diameter than an 18" wheel. When you're referring to wheels, you're referring to diameter. And honestly most of the time it's not a question of the WHEELS "filling out the wheel well" so much as it is the TIRES wrapped around those wheels. Running 37's on 18" wheels will be very different than 34's on 20's.