RV.Net Open Roads Forum: Fifth-Wheels: Axle Ratio, new truck

RV Blog

  |  

RV Sales

  |  

Campgrounds

  |  

RV Parks

  |  

RV Club

  |  

RV Buyers Guide

  |  

Roadside Assistance

  |  

Extended Service Plan

  |  

RV Travel Assistance

  |  

RV Credit Card

  |  

RV Loans

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 Fifth-Wheels

Open Roads Forum  >  Fifth-Wheels

 > Axle Ratio, new truck

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 5  
Prev  |  Next
Sponsored By:
wowens79

Georgia

Senior Member

Joined: 01/05/2015

View Profile


Offline
Posted: 11/04/20 05:20am Link  |  Quote  |  Print  |  Notify Moderator

Reading the gas mileage reports people are posting online, I think driving style has more affect than gear ratio.

Also with the 10spd I don’t think gas mileage around town would be affected. Only when you get on the interstate in 10th would it make any difference.


2002 Chevy Silverado 1500HD 6.0l 241k miles and climbing
2016 Heritage Glen 29BH
2003 Flagstaff 228D Pop Up

dodge guy

Bartlett IL

Senior Member

Joined: 03/23/2004

View Profile


Offline
Posted: 11/04/20 06:06am Link  |  Quote  |  Print  |  Notify Moderator

What people fail to understand is that with a 10 speed trans the trans is rarely in 8, 9 or 10th gear even on the highway. So with 3.73's you will be running in 7th, maybe 8 on flat ground with no head wind. With the 4.30 you will use at least 9th. So the lower gearing (numerically higher) you will be better off especially when towing.

As far as mileage. Towing mileage will increase with the 4.30'
S but may be .5 lower on the highway non towing as compared to 3.73's.

When towing heavy always go with the lower gearing. You and he truck will be happier.


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!


BurbMan

Islip, Long Island

Senior Member

Joined: 09/20/2001

View Profile



Good Sam RV Club Member


Posted: 11/04/20 06:52am Link  |  Quote  |  Print  |  Notify Moderator

I would get the 4.30's. The 10-speed trans will give you decent mileage when not towing, but there's no substitute for that mechanical advantage of lower gearing to get the load moving when you are towing. The 4.30 gears will make it easier for the trans to do its job and will likely help it last longer before it needs a rebuild. The 4.30s will really help when you need it most, like backing into a site...

FWIW, a good axle shop can re-gear a 4x4 for about $2k. Might be worth finding a used one with the 3.73s, then if you don't like how it tows, have it re-geared to 4.30s. I wouldn't sell everything to buy a new truck just to get 4.30s.


2015 Ram 3500 SRW 4x4 Laramie Crew Cab Long Box, Cummins diesel
2002 Lance 811 Slide-In Camper
SOLD: 2008 Terry 34' TT
SOLD: 2001 K2500LT 8.1L Suburban

Lance 811 Renovation Story!
Project Complete!
Maiden Voyage!


valhalla360

No paticular place.

Senior Member

Joined: 08/19/2009

View Profile



Good Sam RV Club Member


Posted: 11/04/20 07:44am Link  |  Quote  |  Print  |  Notify Moderator

dodge guy wrote:

What people fail to understand is that with a 10 speed trans the trans is rarely in 8, 9 or 10th gear even on the highway. So with 3.73's you will be running in 7th, maybe 8 on flat ground with no head wind. With the 4.30 you will use at least 9th. So the lower gearing (numerically higher) you will be better off especially when towing.

As far as mileage. Towing mileage will increase with the 4.30'
S but may be .5 lower on the highway non towing as compared to 3.73's.

When towing heavy always go with the lower gearing. You and he truck will be happier.


The numerical gear of the transmission is largely irrelevant with the new transmissions, with a couple exceptions.

The overall gear ratio from crank shaft to wheel is what counts. Looking up the gear ratios:
- the 4.30 in 8th gear has an overall ratio of 3.66
- the 3.73 in 7th gear has an overall ratio of 3.76

That's within 3% in terms of RPM to maintain the same speed (around 60rpm if in the vicinity of 2000rpm in the gas engine...45RPM if running a diesel at around 1500rpm). So you run in 7th rather than 8th while towing but the engine doesn't know the difference (at least it's close enough not to matter)

Towing mileage isn't going to change as the engine will hold at roughly the same near ideal RPM for the engine.

Non-towing...9th and 10th with the 3.73 is a higher gear (lower numerically) compared to 10th with the 4.30. So when it does get up into those top gears running empty, the higher gears improve efficiency by allowing the engine to keep in the ideal RPM range at higher speeds.

What you describe was true of the older 3-4 speed transmissions where there were big gaps in overall gear ratio between the limited number of transmission gears. It was difficult to get an axle ratio that kept the engine in the ideal RPM range both towing and empty.


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


valhalla360

No paticular place.

Senior Member

Joined: 08/19/2009

View Profile



Good Sam RV Club Member


Posted: 11/04/20 07:50am Link  |  Quote  |  Print  |  Notify Moderator

BurbMan wrote:

I would get the 4.30's. The 10-speed trans will give you decent mileage when not towing, but there's no substitute for that mechanical advantage of lower gearing to get the load moving when you are towing. The 4.30 gears will make it easier for the trans to do its job and will likely help it last longer before it needs a rebuild. The 4.30s will really help when you need it most, like backing into a site...

FWIW, a good axle shop can re-gear a 4x4 for about $2k. Might be worth finding a used one with the 3.73s, then if you don't like how it tows, have it re-geared to 4.30s. I wouldn't sell everything to buy a new truck just to get 4.30s.


If you have a 4x4 and are having difficulty backing into a site...drop it into 4-Lo and you will have far more torque than the 4.30 gives in 2-High. But really, that's a pretty rare issue. Most people towing 15k 5th wheels aren't backing up 20deg inclines.

Accelerating from a stop is simply not an issue with modern drivetrains. The 10 speed will often skip gears because it doesn't need them while accelerating.

Terryallan

Foothills NC

Senior Member

Joined: 06/28/2004

View Profile


Offline
Posted: 11/04/20 04:10pm Link  |  Quote  |  Print  |  Notify Moderator

bucky wrote:

How much does your GCVWR impact your tax and registration costs? With a 10 speed trans the old opinions regarding axle ratios no longer apply.




There really is a reason that lower gears are rated to tow higher weights. Something to do with physics


Terry & Shay
Coachman Apex 288BH.
2013 F150 XLT Off Road
5.0, 3.73
Lazy Campers


Crespro

SoCal

Senior Member

Joined: 07/23/2004

View Profile



Posted: 11/04/20 04:56pm Link  |  Quote  |  Print  |  Notify Moderator

I have the F-250 with 7.3 gas and 4.30 axle. When I am not towing, it runs right at 2,000 rpm at 65 in 10th gear. If you order, by all means get the 4.30.


Crespro 2021 Grand Design 310GK-R, 2020 F250LB, 7.3L, 4.30, Reese 27K

valhalla360

No paticular place.

Senior Member

Joined: 08/19/2009

View Profile



Good Sam RV Club Member


Posted: 11/04/20 05:44pm Link  |  Quote  |  Print  |  Notify Moderator

Terryallan wrote:

There really is a reason that lower gears are rated to tow higher weights. Something to do with physics


Explain the physics for us when both options are well within tow ratings.

BurbMan

Islip, Long Island

Senior Member

Joined: 09/20/2001

View Profile



Good Sam RV Club Member


Posted: 11/04/20 08:00pm Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:

Terryallan wrote:

There really is a reason that lower gears are rated to tow higher weights. Something to do with physics


Explain the physics for us when both options are well within tow ratings.


That's easy...when you operate at a lower % of the rating, you place less stress on the machinery.

valhalla360 wrote:

If you have a 4x4 and are having difficulty backing into a site...drop it into 4-Lo and you will have far more torque than the 4.30 gives in 2-High. But really, that's a pretty rare issue. Most people towing 15k 5th wheels aren't backing up 20deg inclines.


4-lo is Ok sometimes, but not when you have to steer on pavement. What about bumper to bumper traffic when you are caught on the uphill going over a bridge at 5 mph? Taller gears like the 4.30's mean less strain on the transmission. What gears do you have in your F250?

wowens79

Georgia

Senior Member

Joined: 01/05/2015

View Profile


Offline
Posted: 11/04/20 09:16pm Link  |  Quote  |  Print  |  Notify Moderator

Here is how they come up with the tow ratings. They use the SAE J2807 specification.
http://www.trucktrend.com/how-to/towing/1502-sae-j2807-tow-tests-the-standard.

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

Open Roads Forum  >  Fifth-Wheels

 > Axle Ratio, new truck
Search:   Advanced Search

Search only in Fifth-Wheels


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.