Good Sam Club Open Roads Forum: Tow Vehicles: How critical is axle ratio?
Open Roads Forum Already a member? Login here.   If not, Register Today!  |  Help

Newest  |  Active  |  Popular  |  RVing FAQ Forum Rules  |  Forum Posting Help and Support  |  Contact  

Search:   Advanced Search

Search only in Tow Vehicles

Open Roads Forum  >  Tow Vehicles

 > How critical is axle ratio?

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 5  
Prev  |  Next
jaycocamprs

Ringgold Georgia

Senior Member

Joined: 03/28/2004

View Profile





Offline
Posted: 06/14/21 06:48pm Link  |  Quote  |  Print  |  Notify Moderator

And all that goes right out the window as soon as you back up. Only the lower rear gear helps in reverse.


2018 Silverado 3500 DRW
2011 Montana Mountaineer 285RLD


Huntindog

Phoenix AZ

Senior Member

Joined: 04/08/2002

View Profile



Posted: 06/14/21 08:02pm Link  |  Quote  |  Print  |  Notify Moderator

jaycocamprs wrote:

And all that goes right out the window as soon as you back up. Only the lower rear gear helps in reverse.
That is what low range is for.[emoticon]


Huntindog
100% boondocking
2021 Grand Design Momentum 398M
2 bathrooms, no waiting
104 gal grey, 104 black,158 fresh
FullBodyPaint, 3,8Kaxles, DiscBrakes
17.5LRH commercial tires
1380watts solar,800 AH Battleborn batterys
2020 Silverado HighCountryC CD/A 4X4 DRW



time2roll

Southern California

Senior Member

Joined: 03/21/2005

View Profile



Good Sam RV Club Member


Posted: 06/14/21 10:28pm Link  |  Quote  |  Print  |  Notify Moderator

I still have my four speeder. Three when towing. I can only imagine how much better 6, 8, 10+ speeds must be. Not just for the additional ratio width but for the reduced spacing when shifts are made. Swapping my 3.55 to 4.10 made a world of difference towing all these years. I agree with the OP, final drive ratio is not as important anymore. Don't forget the more power also makes a difference as you pass me going just 62 mph with my 260 hp truck. [emoticon]


2001 F150 SuperCrew
2006 Keystone Springdale 249FWBHLS
675w Solar pictures back up

dodge guy

Bartlett IL

Senior Member

Joined: 03/23/2004

View Profile


Offline
Posted: 06/15/21 05:51am Link  |  Quote  |  Print  |  Notify Moderator

Huntindog wrote:

Groover wrote:

Bottom line is that drive shaft RPM is irrelevant. What really matters is whether the engine is in its power band when you need it to be. Back when truck transmissions only had a 2.5 to 1 spread between high and low axle rations where much more important than they are with the newer transmissions that have a 7 or 8 to 1 spread.

The op is correct, unless you find yourself in first gear wishing that you had a deeper gear or in 10th gear wishing that you had a higher gear you get the same effect by simply changing gears.

I do suspect though that axles built with higher ratios may also be built to handle higher torque to the wheels, at least in some cases.
We have a winner. Rather than write all of this again, here is the readers digest version.
GM was late to the party of increasing their HD lines tow ratings. Ford and Ram were first, and they required higher (numericially) ratios to do it. When GM tried this approach, the Pinion gears would not live behind the Dmax. For those that do not know: as the rear end gears increase numericially, the pinion gear engages less of the ring gear, and thus is weaker.
So though the Dmax was more than capable of a higher tow rating, the gear set to make the performance acceptable was out of reach.
Enter GMs new Allison 10 speed. With lower gears available in the tranny, the rear gearset could actually be changed in the direction that would make it stronger. So that is what they did, and for good measure they increased the size of the ring gear on the duallys as well.


What I get out of that is that GM’s axles are weak. No other manuf had that issue with lower gears.


Wife Kim
Son Brandon 17yrs
Daughter Marissa 16yrs
Dog Bailey

12 Forest River Georgetown 350TS Hellwig sway bars, BlueOx TrueCenter stabilizer

13 Ford Explorer Roadmaster Stowmaster 5000, VIP Tow>
A bad day camping is
better than a good day at work!


Hemling

Miami, FL

Full Member

Joined: 06/05/2016

View Profile


Offline
Posted: 06/15/21 06:44am Link  |  Quote  |  Print  |  Notify Moderator

It's like what happened in the 80's when 4 speed overdrive automatic transmissions came out. Before that, you needed a 2.56-3.08 rear to cruise on the highway because of no overdrive, but then automakers started using deeper axle ratios as overdrives became more popular. You could accomplish the same thing with a 2.73 rear and wide ratio 4-speed, but saying 'it's got a 4.10 rear' sounds like it must be much faster. The new automatics have such ungodly low first gears I can't imagine needing a 4.xx anything axle ratio. You must be in first gear for all of half a second (especially when unloaded). I suppose it's all about perspective. Twenty years ago having 500 ft lbs was king, nowadays minivans have 300 horsepower.

Groover

Pulaski, TN

Senior Member

Joined: 10/17/2007

View Profile


Offline
Posted: 06/15/21 06:47am Link  |  Quote  |  Print  |  Notify Moderator

Huntindog wrote:

jaycocamprs wrote:

And all that goes right out the window as soon as you back up. Only the lower rear gear helps in reverse.
That is what low range is for.[emoticon]


For the transmissions that I have looked up gear ratios for reverse gear ratio roughly follows first gear. So buyers of those transmissions do have a much lower reverse gear than was previously offered with a 4 speed transmission and the lowest axle ratio combination.

valhalla360

No paticular place.

Senior Member

Joined: 08/19/2009

View Profile



Good Sam RV Club Member


Posted: 06/15/21 07:33am Link  |  Quote  |  Print  |  Notify Moderator

Looking at the 2015 F150 6 speed:
1st: 4.17
2nd: 2.34
3rd: 1.52
4th: 1.14
5th: 0.86
6th: 0.69

With a 3.73 in 1st gear, that's an overall ratio of 15.55.

Ford 2017 10 speed:
1st: 4.69
2nd: 2.98
3rd: 2.14
4th: 1.76
5th: 1.52
6th: 1.27
7th: 1.00
8th: 0.85
9th: 0.68
10th: 0.63

With a 3.31 rear end in 1st gear, that's an overall ratio of 15.52

That's less than 0.2% lower overall gear ratio in 1st gear. With newer motors being stronger, I would give the edge to the 10speed with the lower (numerical) gear ratio but not much difference.

And as someone mentioned, if you have 4x4, you can drop down into low range and make crazy torque at the wheels regardless for low speed manuvering.

Reverse: The 6 speed is 3.40 (12.68 overall ratio). The 10 speed is 4.86 (16.09 overall ratio)...the 10speed with lower (numerical) rear end ratio, has a significantly deeper overall reverse ratio.

As long as you aren't exceeding the max tow limits, there really isn't an advantage in getting a higher (numerical) rear end. Especially if you only tow a small percentage of overall truck miles.


Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV


kellem

Shenandoah valley,VA

Senior Member

Joined: 05/07/2007

View Profile


Offline
Posted: 06/15/21 07:35am Link  |  Quote  |  Print  |  Notify Moderator

The 10spd transmission does negate some of the downfalls of towing with 3.55 vs 4.30 but at the same time allows 4.30's to run comfortably at highway speeds.

The 4.30 does however have a higher towing spec than 3.55.
Avoid a marginal tow vehicle and it becomes a non issue.

We're towing a 7600# 30ft trailer with a F250 7.3 10spd with 3.55 gears and you are correct, the 10spd is a game changer for sure.

Boomerweps

Hills of PA

Senior Member

Joined: 04/30/2018

View Profile


Offline
Posted: 06/15/21 07:47am Link  |  Quote  |  Print  |  Notify Moderator

Did you note that the previous Ford 6 speed upper two gears were overdrive?
And the current 10 speed (shared with other makers) upper three speeds are overdrives.

The transmission & axel ratio combine to put the engine torque to the wheels. So a decent axle ratio still matters. Towing at speed is one thing but, IMO, it’s the starting energy and loss of energy on hills that gets noticed.


2019 Wolf Pup 16 BHS Limited, axle flipped
2019 F150 4x4 SCrew SB STX 5.0 3.55 factory tow package, 7000#GVWR, 1990 CC Tow mirrors, TBC


valhalla360

No paticular place.

Senior Member

Joined: 08/19/2009

View Profile



Good Sam RV Club Member


Posted: 06/15/21 08:34am Link  |  Quote  |  Print  |  Notify Moderator

kellem wrote:

The 10spd transmission does negate some of the downfalls of towing with 3.55 vs 4.30 but at the same time allows 4.30's to run comfortably at highway speeds.


And empty, the 4.30 will max out in 10th gear then run at higher than needed RPM, so the engine isn't optimized.

So unless a large percentage of miles are towing at the max limits, you don't gain anything.

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 5  
Prev  |  Next

Open Roads Forum  >  Tow Vehicles

 > How critical is axle ratio?
Search:   Advanced Search

Search only in Tow Vehicles


New posts No new posts
Closed, new posts Closed, no new posts
Moved, new posts Moved, no new posts

Adjust text size:




© 2021 CWI, Inc. © 2021 Good Sam Enterprises, LLC. All Rights Reserved.