acdii

I keep forgetting about the 10 speed tranny. It is a real game changer when it comes to towing and hauling. So used to the 6 speed after driving with it for 3 years and two different trucks. Wishing I had found a 17 that fit my needs when I got the 16.

I tried searching for that truck I saw, but it must have been sold, it was in Kansas.

8100hd

Less sidewall doesn’t necessarily mean less flex. LT tires will have a stronger 3 ply+ sidewall and P rated tires have 1 or 2. NHTSA tests show LT tires can take twice the sidewall force of a similar sized P tire though it will flex more before rupturing. I doubt there much difference in flex between a P275\55R20 and a LT275\65R18C running at max rated pressures. You will probably see the P rated tire weigh in at 5-10 lbs less then the LT in those sizes.

acdii

LT vs 20" I have had both on my 16, the Wrangler LT and Bridgestone Duellers. The Duellers on 20 wheels had a much firmer ride empty and towing, the LT you can really tell the sidewalls are taller. I found no benefit running the factory LT tires when towing with my trailer, but of course YMMV.

8100hd

The sidewall height difference between a lt275\65R18 and a 275\55R20 is one inch, so it’s not really all that much.

acdii

7.04 vs 5.95 to be exact. Overall circumference though is 100.78 vs 100.22, so the 20's are slightly smaller in diameter and height.

smokeywren

Read it again.


For 2018 F-150, HDPP includes 3.73 E-Locker. Max tow includes 3.55 e-Locker BUT axle is changed to 3.73 e-locker if max tow is ordered with HDPP.

atwowheelguy

The ten speed makes a difference. 4.69 first gear instead of 4.17 on the six speed. 4.69/4.17 = 1.125

So the old 3.55 performance now feels like a 3.99 six speed would.
The old 3.73 now feels like a 4.20 six speed would.

On the other end, top gear is 0.63 instead of 0.69. 0.63/0.69 = 0.913
So the old 3.55 now revs like a 3.24 six speed would.
The old 3.73 now revs like a 3.41 six speed would.

I have a '13 3.5 EB 3.55 with a GCWR of 15,300.
The new '18 3.5 EB 3.15 has a GCWR of 15,800.

When trade time comes, I'm going with the 3.15 ten speed to replace my 3.55 six speed.

8100hd

The tire height for the 20’s is 31.91 inches vs 32.07 inches on the 18’s. The reason the HDPP trucks get the LTs is because of the increased load capacity. There’s nothing special about those 20’s from a load carrying and towing point of view, you can put them in the “just enough to get by” category.

Gladehound

The 10-speed certainly does make a difference. The flexibility of the 10-speed makes rear end gearing selection less critical than it was with the 6-speed.

Back in the days when we only had 3 gears to select from and big thirsty 400+ cube engines, picking the proper rear end was serious business! Good highway MPG and good low speed towing performance were hard to get in one package.

Now, with the 10-speed and small forced induction engines, it's a much less critical decision. If you live in a state with 80 mph speed limits and you run a lot of empty highway the 3.15 is probably a good choice. If you tow all the time the 3.73 will make life easiest on the transmission. But that 10-speed will allow either set up to do the others designated job surprisingly well. Keep in mind that small forced induction engines often get better MPG with a few extra revs and a little less boost. With a triple OD on the 10-speed, the 3.15 might not always get the best highway MPG. And differences in towing performance and MPG due to rear gear ratio selection are smaller now than ever before.

acdii

I pointed out in a previous post where I found the documentation and stood corrected, so no need to rehash my oversight on the gearing! :P

I can tell you from experience that the 3.15, with a 6 speed, got better MPG at highway speeds than 3.55 with a 6 speed. It ran at a lower RPM before boost, where the 3.55 runs at a higher RPM in boost. Makes a 3 MPG difference. Since I have not driven the 10 speed, I would like to see what the differences are. I would much rather have the 3.31 in my current truck than the 3.55, split the difference between the 3.15 and 3.55 for better MPG in my daily drive and have decent towing capabilities for my summer trips. Towing with the 3.15 was OK, but the drone of driving at 60 MPH in 4th was wearing on the senses.