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Robin Hood

New Build...Axle Ratio and GVWR opions requested

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Posted (edited)

^^^^ I’d like to challenge you to come up with a scenario towing a typical 16000 lb RV where a 6.7 powered Ford 10 speed SRW with 3.55 gears will out perform the same truck with 3.31 gears. Then think about the number of times you might encounter those conditions. I believe the 3.55 gears are more suited once you get into towing trailers heavy enough to  require duals.

Edited by 4x4ord

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Considering the original poster was talking about towing 18k which is what we are talking about which is also near max towing I would take the 3.55. No I am not going to engage in arguing about what scenario you have dreamt up. I have read your posts on the other forum. No need for you to preach about what I need or someone else needs. There are 2 options and we can get what ever we choose is best for us. 

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^^^^ it’s not a big deal.... 3.55s will do just fine and if you’re willing to pay a little extra at the pump each time you fill up to gain the warm fuzzies you get knowing that you have 3.55 gears that’s your business. I think most of us are not willing to sacrifice mileage to gain nothing.

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Posted (edited)

Seeing as the OP is looking at getting 2 trucks maybe he will get one of each gear sets, it would be a great comparison. I’m looking forward to pulling my trailer in a couple weeks, it’s a lot cheaper to run than my gas truck was. I hope you get to do the same with yours. 

Edited by Ramrod79

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Great points and good conversation! The two trucks will be used for totally different purposes and will have different towing loads, so it won't be a great comparison. I have already ordered the first truck and went with the 3.55 and 11,400 GVWR. Personally, I don't monitor my fuel mileage that close and I don't drive in a way that maximizes fuel milage anyways. With that said, if the computers and transmission control is that good, I'm still not convinced that a 3.31 will be better overall unless you are driving at 80 plus MPH. The truck I ordered will be used mostly around town.

 

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For me it all depends on what's being towed and where. Trailers with very little frontal area. 3.31 would be fine. Enclosed trailer, campers and such with huge frontal area and poor aerodynamics. 3.55's if not lower. The best way to decide which way to go, is talk to people who tow the same trailer with the vehicle you plan on.

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Posted (edited)

I think it would be interesting to ask people who have 3.31 gears how often they use tenth gear. My guess is that for most, 10th will be one of the most used gears. When it comes right down to it a 3.55 equipped truck is very similar to a 3.31 with 10th locked out.

 

With 3.31 gears I find I lock out 10th and occasionally even 9th while towing in certain conditions..... conditions where I’m towing heavy enough to be getting 6 mpg

Edited by 4x4ord

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I did a little digging to help me understand the differences between the 6 speed and ratios I currently have, verse the 10 speed now available. Am I reading and understanding this correctly? With the new 10 speed, the final drive is actually a little lower than the previous 6 speed?. I would have thought it would have been higher with the extra 4 gears. The final ratio with a 3.31 is 2.22 for the 6 speed verse 2.27 with the 10 speed and the final ratio with a 3.55 is 2.38 with the 6 speed verse 2.44 with the 10 speed.

 

This would lead me to believe that what currently bothers me about my 3.31, may not be an issue with the 10 speed.

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Either gear set will do the job Robin Hood,  the 3.55 just gives you a little more mechanical advantage when towing that big fifth wheel you have. 

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With the 10 speed you don't need to worry about which gearing you have on F250/350 SRW.

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Posted (edited)
19 hours ago, Robin Hood said:

I did a little digging to help me understand the differences between the 6 speed and ratios I currently have, verse the 10 speed now available. Am I reading and understanding this correctly? With the new 10 speed, the final drive is actually a little lower than the previous 6 speed?. I would have thought it would have been higher with the extra 4 gears. The final ratio with a 3.31 is 2.22 for the 6 speed verse 2.27 with the 10 speed and the final ratio with a 3.55 is 2.38 with the 6 speed verse 2.44 with the 10 speed.

 

This would lead me to believe that what currently bothers me about my 3.31, may not be an issue with the 10 speed.

I think you might have a wrong number there. 
3.31 ten speed overall drive ratio in 10th is 3.31 x .632 = 2.092

six speed is 3.31 x .674 = 2.231

 

But comparing the 2021 Powestroke to the 2019 is a little more involved:

 

The 2021 makes 1050 lbft peak torque at 1600 rpm .... 320 hp @ 1600 rpm.

 

The 2019 makes 935 lb ft peak torque at 1800 rpm. ... 320 hp @ 1800 rpm.

 

So, even though the six speed is geared lower in high gear than the ten speed is consider this: 

 

At 77 mph a 3.31 equipped 2021 Powerstroke would be running at 1600 rpm and able to produce 320 hp

At 76 mph a 3.55 equipped 2019 Powerstroke would be running at 1800 rpm and able to produce 320 hp. 
So even though the ten speed has a higher high gear ratio than the six speed it still takes 3.55 gears with a six speed to compete with 3.31 gears in a 2021. 

 

Also, just because you have 10 gears doesn’t mean you always have to use high gear. There is nothing wrong with locking out tenth gear on occasion if conditions warrant the practice.
 

 

Edit: And I think it’s worth mentioning again that it would take 4.30 gears behind a 2019 / six speed for first gear to compete with first gear and 3.31 gears behind a 2021 / ten speed. (And 5.00 or even 5.50 rear end behind a 2019 to compete with a 2021 in reverse)

 

Edited by 4x4ord
Add a bit of info

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Robin Hood/4x4ford, your calculations got me interested in the complete spread of the 10 vs 6spd gear ratio so I did these calculations for a comparison. The comparison of the 4.10 vs the 4.30 is very close as well. That reverse gear ratio would sure be nice. Sadly I have a few more years with my 19 before I upgrade. 

2E6D88F7-3E45-48A4-9EE8-B7B8713C07A6.jpeg

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My opinion, the main reason for the two different ratios comes down to tire size. And it's so slight, Ford doesn't even force one over the other. If they did it would be 3.31 ratio with 18"  & 3.55 ratio with 20". In tenth gear with 18" & 3.31 ratio at 65mph you're at 1423 rpm. 20" & 3.55 ratio at 65mph you're at 1428. 18" And 3.55 it's 1526 rpm. 20" & 3.31 it"s 1332 rpm.

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t

1 hour ago, ttwn0324 said:

My opinion, the main reason for the two different ratios comes down to tire size. And it's so slight, Ford doesn't even force one over the other. If they did it would be 3.31 ratio with 18"  & 3.55 ratio with 20". In tenth gear with 18" & 3.31 ratio at 65mph you're at 1423 rpm. 20" & 3.55 ratio at 65mph you're at 1428. 18" And 3.55 it's 1526 rpm. 20" & 3.31 it"s 1332 rpm.

twn0324, have you done the calculations with the 17” tires?  I like those calculations it really shows depending on which wheel size you went with it could increase or decrease the gap between the 2 gear sets.   

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On 5/2/2021 at 7:42 PM, Ramrod79 said:

twn0324, have you done the calculations with the 17” tires?  I like those calculations it really shows depending on which wheel size you went with it could increase or decrease the gap between the 2 gear sets.

No, I haven't. I think the tire circumference for 17" rims are 31.5" that Ford lists. 18" are 32.1". The 17" tires would be like 25-30 rpm's higher then the 18" non Tremor tires. The Tires on the Tremor are like 34.8" compared to 34.1" for 20'" rims. The Tremor Tires would run 28-35 rpm's lower then the 20" tires. 

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Posted (edited)

I don’t think the Tremor is available with 3.31 gears. 

Edited by 4x4ord

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3 hours ago, 4x4ord said:

don’t think the Tremor is available with 3.31 gears. 

It's not. 3.55 ratio for 6.7l and 4.30 ratio for the 7.3l. 

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