F150 3.15 axle 10 speed equals 3.55 axle 6 speed

blackgrizz550 wrote:

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I towed my camper with it for the first time last weekend. It did decide to kick down to second gearing while braking down a hill. 5,500 RPM's seemed a little excessive. Other than that, it worked fine. It likes 7th gear mostly while towing.

Would manually run my 2011 (6spd, 3.73) that high in 2nd down some steep Appalachian trails to get enough engine braking. But I didn't like it either. The Ecoboost is a great engine other than it's weak engine braking.

TurnThePage wrote:
I'm interested in more real time reviews of that 10 speed transmission. Everything I've read/heard so far doesn't make it sound all that awesome. Maybe just some fine tune programming...

We have almost 4,000 miles on ours. It does shift funny when everything is cold. Once the engine/transmission are warm it shifts fine.

I towed my camper with it for the first time last weekend. It did decide to kick down to second gearing while braking down a hill. 5,500 RPM's seemed a little excessive. Other than that, it worked fine. It likes 7th gear mostly while towing.

time2roll wrote:
Anyone have a 2017 EPA number for 3.15 vs 3.55?
I cannot seem to find much where is ratio is called out.

I believe this is a comparison of the 3.15 (standard) vs. 3.15 with LT tire vs. 3.73 (HDPP).
City: 18 18 17
Hwy: 25 23 22
Combined: 21 20 19
I expect that the 3.55 would be between the 3.15 and the 3.73.

Note the 14% increase in hwy mpg, 22 vs 25, 3.73 vs 3.15.

time2roll wrote:
Anyone have a 2017 EPA number for 3.15 vs 3.55?
I cannot seem to find much where is ratio is called out.

I doubt there's any real world difference. The 8 / 10 speeds have such tight ratio spread, the rear axle differences becomes almost negligible.

Here's a fund fact, if you look at the chart in the OP, compare a 10 speed 3.15 truck to a 10 spd 3.73 truck, you'll see an interesting pattern: once past 2nd gear, the ratios are almost identical, if the 3.73 truck is in a higher gear!

In a towing situation, if you need 5th in the 3.15 truck, you'd simply pick 6th in the 3.73 truck, and perform nearly identical.

RAM did the same with their 8 spds, a lower gear in the 3.21 truck is nearly identical with a higher gear in the 3.92 truck. When buying, your only decision is - do you value low hwy RPM or super low crawl ratio?

Once you answer that question, gears 3 - 9 makes no difference.

Anyone have a 2017 EPA number for 3.15 vs 3.55?
I cannot seem to find much where is ratio is called out.

Huntindog wrote:
It is a choice. Do you want better performance when towing? Or better MPGs when empty?
The different rear axle ratios WILL make difference. Neither choice is "wrong" or "right".

The 3.55 will have the effect of making it a close ratio trans... IOW, the motor will operate at it's powerband peak more. This will change the personality (so to speak) of the truck, and it will just make for a better tow, and probably a little better MPGs when towing. At the expense of sacrificing in MPGs when empty.

When deciding, you gotta consider just how much you tow, and how demanding your towing conditions are.. There is more to it than just looking at rpms @ a certain speed. How you get to that speed matters as well.

IOW, if you have two indentical trucks/trailers with only the rear axle ratios different. And drive them both.... One WILL impress you more. In this case, the 3.55 truck.

Unhitch the trailers, and the difference is mainly gonna show up as better economy for the 3.15 truck.

Your money. Your choice.

Yes. That's the whole point of this post. I have already discovered with 8,000 miles of towing that the 3.5 EB with the 6 speed 3.55 with the 14.80 first gear ratio does a fine job of towing my 6600 lb. camper. It is "good enough". In fact, it's great. I don't need a lower first gear. I see no reason why the new 3.5 EB with the 10 speed 3.15 with the nearly identical 14.77 first gear ratio will not do an equally fine job. But the 10 speed gives the advantage of lowering the engine speed in the top gear by 19% by lowering the gear ratio from 2.45 to 1.98. My towing miles are 8,000/105,000 = 7.6% of the truck's total miles so far. The low range gearing power is good enough and I would be sacrificing nothing there with the 3.15 ten speed, and the better mileage would apply to many more miles. I don't see a downside.

time2roll wrote:
So it is not entirely the transmission... Extra 12 percent torque makes a difference too.
3.55 to 4.10 is 15 percent.

Put both behind the same engine and the 4.10 to 3.55 is not as exciting.

That is the whole point. The greater engine torque output and more gears you have, the shorter rear end ratio you are able to run without sacrificing capabilities.

Take my Ram for instance. Since torque output of the Cummins 6.7L has increased from 650 lb-ft in 2010 to 800 lb-ft in 2014, my 2014 with a 3.42 axle ratio is putting down more torque to the rear wheels in every gear than the equivalent 2010 Cummins with a 3.73 rear ratio and the same 6 speed trans. The concept is similar to "downspeeding" that it has been used in the heavy duty on-highway world for years to increase fuel efficiency.

time2roll wrote:

ShinerBock wrote:
So you expect to be able to use all of your gears in any situation when towing? I am not sure what your towing experience is and I am not trying to insult, but most vehicles are not able to use all of their transmission gears in every situation when towing heavy (or even moderate loads for some) regardless if the have a 5, 6, 8, or 10 speed transmission.

Most current 6 speeds have two overdrives which are 5th and 6th gears. With my 2014 Cummins, my 6th is utilized as my overdrive when unloaded and towing light loads for better fuel economy. I lock out 6th and use 5th as my overdrive when towing moderate to heavy loads on the highway. Again, for better fuel economy and to keep the EGT's in check.

Just because you have all those gears, doesn't mean you have to use them in every situation. They are there to keep the engine in its power band and have enough torque multiplication to keep the vehicle moving forward. Heck, even tractor/trailers with 13 or 18 speeds are not able to use all gears in every situation when towing.

The top gears for fuel economy are not a big concern to me. But to lose 4 of your gears all at the top seems poorly balanced. I would rather be in the middle 6 ratios for normal conditions. For economy I would have 2 more at the top, and for an unexpected steep condition have two more at the bottom. A lower 4.10/4.56 would present this flexibility. I would worry more about getting started on a 15+ percent incline more than a bit of economy.

I understand those tractor/trailers don't always use the lowest gear to get moving. Or do they?

4.1/4.56 does not gain flexibility. It eliminates it. Now you have a vehicle set up for one purpose. At that point purchase the big truck and be done with it.

So it is not entirely the transmission... Extra 12 percent torque makes a difference too.
3.55 to 4.10 is 15 percent.

Put both behind the same engine and the 4.10 to 3.55 is not as exciting.

time2roll wrote:
The top gears for fuel economy are not a big concern to me. But to lose 4 of your gears all at the top seems poorly balanced. I would rather be in the middle 6 ratios for normal conditions. For economy I would have 2 more at the top, and for an unexpected steep condition have two more at the bottom. A lower 4.10/4.56 would present this flexibility. I would worry more about getting started on a 15+ percent incline more than a bit of economy.

I don't see how you would say that you would lose 4 gears at the top? If you look at the pictures posted by the OP of the 3.73 ratio in both the 6 and 10 speeds, you will see that the 6 speed 6th gear is close to 10 speeds 9th gear. The 6 speeds 5th gear is close to the 10 speeds 8th gear. The 6 speeds 4th gear is the 10 speeds 6th gear and so on.

I know with towing close to 10k in my old 2011 F150 3.5L Ecoboost with 3.73 gears, it would easily hold 5th towing that much which means that the 10 speed would easily hold 8th gear since those two gears are similar. In fact, if you factor in the 50 lb-ft of added peak torque in the new gen 2 Ecoboost, the 6 speeds 5th gear is putting 1,348 lb-ft to the wheels and the 10 speeds 8th gear is putting more at 1,489 lb-ft to the wheels.

And if you compare a 6 speed 4.10 to a 10 speed 3.55 on how much lb-ft each are putting to the wheels factoring the added peak torque of the new EB, you will see that a 10 speed 3.55 will easily go tow to tow(pun intend) with the 6 speed 4.10.

420 lb-ft Gen 1 EB 6 speed w/4.10
1st: 7,182 lb-ft
2nd: 4,028 lb-ft
3rd: 2,617 lb-ft
4th: 1,961 lb-ft
5th: 1,482 lb-ft
6th: 1,189 lb-ft

470 lb-ft Gen 2 EB w/3.55
1st: 7,826 lb-ft
2nd: 4,973 lb-ft
3rd: 3,572 lb-ft
4th: 2,938 lb-ft
5th: 2,538 lb-ft
6th: 2,120 lb-ft
7th: 1,669 lb-ft
8th: 1,419 lb-ft
9th: 1,133 lb-ft
10th: 1,053 lb-ft

There is also the factor that high rpm turbocharged engines benefit more from taller gears due to being able to utilize there low end torque and broader power band. Basically you are staying in lower gears with its torque multiplication longer. It is mainly N/A engines that benefit more from shorter gearing since their power is higher in the rpm.

time2roll wrote:
I understand those tractor/trailers don't always use the lowest gear to get moving. Or do they?

Not when unloaded. You can start in 3rd of 4th when unloaded. Heck, you can even bypass gears going from 3rd to 6th just like I heard this Ford 10 speed does.