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New Build...Axle Ratio and GVWR opions requested


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I'm looking for opinions on two new builds, regarding axle ratio and GVWR. Both trucks will be F350, SRW, CC, 4X4, diesel, long bed trucks. One will be driven empty around town or towing a 37' 5th wheel, weighing 18K. The other will be driven empty around town or towing bumper pull trailers, weighing 12K to 14k pounds. For the purpose of this discussion, lets assume the use is split 50/50.

 

Both of my current trucks are 11,400 GVWR. I added bags to the truck pulling the 5th wheel and ideally I should add bags to the other truck. Neither one was bad, but didn't sit level. The truck with the bags rides really nice, so I am afraid to over spring the truck with a higher GVWR for around town driving.

 

The truck I use for bumper pull is a 3.31 axle and I hate it. I tend to downshift to 5th around town, even when I am not towing. The truck used with the 5th wheel is a a 3.55 and I like it a lot better. I was planning to order a 3.55 on both new trucks, but I read in another post, that a 3.55 and a 3.73 are so close that there is not reason not to go with the 3.73. So that got me thinking, should both trucks be 3.73 or is that to much gear when I'm not towing.

 

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20 hours ago, Robin Hood said:

I'm looking for opinions on two new builds, regarding axle ratio and GVWR. Both trucks will be F350, SRW, CC, 4X4, diesel, long bed trucks. One will be driven empty around town or towing a 37' 5th wheel, weighing 18K. The other will be driven empty around town or towing bumper pull trailers, weighing 12K to 14k pounds. For the purpose of this discussion, lets assume the use is split 50/50.

 

Both of my current trucks are 11,400 GVWR. I added bags to the truck pulling the 5th wheel and ideally I should add bags to the other truck. Neither one was bad, but didn't sit level. The truck with the bags rides really nice, so I am afraid to over spring the truck with a higher GVWR for around town driving.

 

The truck I use for bumper pull is a 3.31 axle and I hate it. I tend to downshift to 5th around town, even when I am not towing. The truck used with the 5th wheel is a a 3.55 and I like it a lot better. I was planning to order a 3.55 on both new trucks, but I read in another post, that a 3.55 and a 3.73 are so close that there is not reason not to go with the 3.73. So that got me thinking, should both trucks be 3.73 or is that to much gear when I'm not towing.

 

 

With 10 speed transmission you essentially have extra gears.  Are you sure you want SRW with an 18K 5th wheel?  Lots of people end up switching to DRW with that size trailer.

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13 hours ago, Ford truck guy said:

I believe that you cannot ADD 3.73's to a diesel.. adding those will make you drop to the 6.2 gas....  BUT, I may be wrong

 

13 hours ago, akirby said:

 

You are correct.   Diesel only allows 3.31 and 3.55.

 

thanks!...Yep, it showed as an option and it never crossed my mind it wasn't available. That pretty much answers one question.

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1 hour ago, ScottK1 said:

 

 

With 10 speed transmission you essentially have extra gears.  Are you sure you want SRW with an 18K 5th wheel?  Lots of people end up switching to DRW with that size trailer.

Positive about the SRW, but only with a long bed. My current truck pulls the trailer with no issues at all. It's a pleasure to drive and very predictable..

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1 hour ago, road turtle said:

Analysis I saw in RV dot net, the 3.31 is better for towing than 3.55.  I don't recall if you can step up to 4.3(?).

 

18k is going to have a heavy pin weight.  You may be undersized for payload capacity with SRW.

 

If I read the same thing, I'm not sure I agree. It would definitely take some more convincing. Anyone else want to chime in on this?

 

Edited by Robin Hood
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I'll go..  My 2020 Redwood is 17,500# ready to roll....... the difference from my old 2015 F-350 to my 2020 F-350 is truly night and day...   With the new trucks, the new norm for DRW has shifted a bit higher.. Although, I am only a weekend warrior and do not put a ton of miles on, once I go to fulltime, I will be in a DRW.. I have panic stopped with zero issues... I have been in 40 mph cross winds with zero issues.... never have I felt the tail wagging the dog...

 

 

 

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12 hours ago, Ford truck guy said:

Thanks... no Arctic Fox dealers were near us when we ordered our first Redwood back in 2015

 

Did you order or buy off the lot? What gear ratio did you go with and why? What GVWR package is on the truck. It looks like the rear end squats just a little, do you wish you had a higher GVWR or bags? Would you do anything different if you ordered today?

Edited by Robin Hood
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2 hours ago, Robin Hood said:

 

Did you order or buy off the lot? What gear ratio did you go with and why? What GVWR package is on the truck. It looks like the rear end squats just a little, do you wish you had a higher GVWR or bags? Would you do anything different if you ordered today?

 

I special ordered. I wanted the 3.55 and 12,400 GVW.. The 1st picture (in my driveway )  was my first trip with the truck before bags..... I have Firestone Ride Rite bags aired to 35 when towing to level it out. For our camping needs, I wouldn't want anything else right now.

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5 hours ago, Ford truck guy said:

 

I special ordered. I wanted the 3.55 and 12,400 GVW.. The 1st picture (in my driveway )  was my first trip with the truck before bags..... I have Firestone Ride Rite bags aired to 35 when towing to level it out. For our camping needs, I wouldn't want anything else right now.

 

How does the truck ride when empty in the back with the 12,400 GVWR?

 

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2 hours ago, Robin Hood said:

 

How does the truck ride when empty in the back with the 12,400 GVWR?

 

 

Like a dream.... I drop my bags down to 5psi and run it.... With the long bed, the wheelbase allows the truck to glide more over bumps, then choppy like the short Beds.... 

 

This is by far the very best riding truck I have ever driven....Night and Dy better than my 2015 F-350

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  • 3 weeks later...

The new Powerstroke/10 speed can't be compared to the previous generation. I would go 3.31 axle ratio for both trucks. 9nth gear with 3.31 gears is almost identical to 10th gear with 3.55 gears. If  you have 3.31 gears and you find yourself towing in conditions such that 10th is not desired you simply click the minus on the shift lever and 10th is locked out and the engine is revving just slightly higher than what a 3.55 equipped truck would be at in 10th. If you hit a slight hill the transmission will drop to 8th or 7th where the engine will be revving higher than the 3.55 equipped truck would be revving in 9th or 8th. At 62 mph with 3.31 gears you are at 2029 rpm in 7th where as the 3.55 equipped truck will be running at 1850rpm in 8th. If the hill is steep enough to require another shift the 3.31 equipped truck will go to 2591 rpm where it makes peak HP. The 3.55 equipped truck will have a choice between dropping one gear where it would be at 2176 rpm or dropping two gears and revving to 2780 rpm.... neither gear would allow it to keep up to the 3.31 equipped truck. The new Powerstroke will pull an 18000 lb rv up a 6% grade at 62 mph so it is not till you are on steeper grades than 6% with 18000 lbs in tow that the 3.55 gears will keep up with or possibly overtake 3.31 gears.  I find it rare that I lock out 10th and often that I appreciate having 10th gear.Basically if I had 3.55 gears it would be as though I'm giving up 10th gear. Another fact to keep in mind when you are thinking gear ratios with the new 10 speed is that a 3.31 equipped 2021 Powerstroke is capable of putting more torque to its rear axle in 1st gear than what a 2019 F450 with 4.30 gears could put to its rear axle in 1st gear.

Edited by 4x4ord
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13 hours ago, 4x4ord said:

The new Powerstroke/10 speed can't be compared to the previous generation. I would go 3.31 axle ratio for both trucks. 9nth gear with 3.31 gears is almost identical to 10th gear with 3.55 gears. If  you have 3.31 gears and you find yourself towing in conditions such that 10th is not desired you simply click the minus on the shift lever and 10th is locked out and the engine is revving just slightly higher than what a 3.55 equipped truck would be at in 10th. If you hit a slight hill the transmission will drop to 8th or 7th where the engine will be revving higher than the 3.55 equipped truck would be revving in 9th or 8th. At 62 mph with 3.31 gears you are at 2029 rpm in 7th where as the 3.55 equipped truck will be running at 1850rpm in 8th. If the hill is steep enough to require another shift the 3.31 equipped truck will go to 2591 rpm where it makes peak HP. The 3.55 equipped truck will have a choice between dropping one gear where it would be at 2176 rpm or dropping two gears and revving to 2780 rpm.... neither gear would allow it to keep up to the 3.31 equipped truck. The new Powerstroke will pull an 18000 lb rv up a 6% grade at 62 mph so it is not till you are on steeper grades than 6% with 18000 lbs in tow that the 3.55 gears will keep up with or possibly overtake 3.31 gears.  I find it rare that I lock out 10th and often that I appreciate having 10th gear.Basically if I had 3.55 gears it would be as though I'm giving up 10th gear. Another fact to keep in mind when you are thinking gear ratios with the new 10 speed is that a 3.31 equipped 2021 Powerstroke is capable of putting more torque to its rear axle in 1st gear than what a 2019 F450 with 4.30 gears could put to its rear axle in 1st gear.

 

What size tires did you use in your analysis?

 

You use 62 mph as an example, but wouldn't it be true at other speeds the 3.55 would be in the sweat spot of the powerband when the 3.31 is not? I get the fact that you are giving up the highest overdrive gear, but you gain closer ratios throughout the 10 speeds which should lead to quicker acceleration and smoother shifts, not to mention isn't the 3.55 a stronger ring gear? Can you direct me to a link that compares the 6 speed gear ratios to the 10 speed gear ratios?

 

Edited by Robin Hood
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^^^ Yes it is true that at different speeds the math would work out different but at slower speeds the Powerstroke could pull even steeper grades without breaking a sweat. The 3.55s would put the Powerstroke at the rpm where it makes peak Hp at 74 mph in 7th gear. At 74 mph the 3.31 equipped truck would be at about 2422 rpm in 6th gear where the Powerstroke is able to put out 450 Hp. I think 74 mph is a little fast for mountain road towing.

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2 hours ago, 4x4ord said:

^^^ Yes it is true that at different speeds the math would work out different but at slower speeds the Powerstroke could pull even steeper grades without breaking a sweat. The 3.55s would put the Powerstroke at the rpm where it makes peak Hp at 74 mph in 7th gear. At 74 mph the 3.31 equipped truck would be at about 2422 rpm in 6th gear where the Powerstroke is able to put out 450 Hp. I think 74 mph is a little fast for mountain road towing.

 

What size tire are you using to run your calculation?

 

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3.55’s for me, if I was pulling that kind of weight I would want the lower gears. I am only towing about half what you are Robin Hood(I have the 6spd).  I’m sure the newer engine and trans combo would pull just fine with either gear set but I would take the 3.55 for the better off the line and it would be better for reversing with a heavy trailer as well.  

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^^^ Keep in mind that the 2021 3.31/10 speed equipped truck can put more torque to the rear axle in first gear than a 2019 4.30/6 speed equipped truck can.  And in reverse a 2019/6 speed would need 5.0 rear gears to put the level of torque to the rear axle that a 3.31 equipped 10/speed can. 

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1 hour ago, 4x4ord said:

^^^ Keep in mind that the 2021 3.31/10 speed equipped truck can put more torque to the rear axle in first gear than a 2019 4.30/6 speed equipped truck can.  And in reverse a 2019/6 speed would need 5.0 rear gears to put the level of torque to the rear axle that a 3.31 equipped 10/speed can. 

MOAR POWER :)

 

Thank you for the detail breakdown.  I ordered the F350 with 3.31 based on your analysis.  And the fact my new 5er GVWR is 14,300, I should be in awesome shape!

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Fully aware of what the new truck will do but if you are buying a truck for towing why not go with the lower gear set?  The 3.31 gear set would have done just fine with what I am currently towing but when I upgrade my trailer I know the 3.55 will be the right choice for me. 

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