Woodalls Open Roads Forum: Tow Vehicles: 3.55 vs 3.73 rear end question
Open Roads Forum Already a member? Login here.   If not, Register Today!  |  Help

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

Search:   Advanced Search

Search only in Tow Vehicles

Open Roads Forum  >  Tow Vehicles

 > 3.55 vs 3.73 rear end question

This Topic Is Closed  |  Print Topic  |  Post New Topic  | 
Page of 5  
Next
ezgoin

Sunny Arizona

Senior Member

Joined: 07/09/2003

View Profile



Good Sam RV Club Member


Posted: 01/11/11 09:48pm Link  |  Print  |  Notify Moderator

Ok, I'm not much of a car guy so I have a pretty basic question. I see all this info about the 3.73 axle being best for towing, but I was doing a build price on Ford's web site and you can't get the 3.73 in the 4x2 SuperCab 145" wheelbase (6 1/2' bed)..... only the 3.55 axle. So how much difference is the pulling ability between the two? What would be the difference in performance?

You can get the 3.73 in the Regular cab 145" wheelbase (8' bed). I would need the 145" wheelbase so it would fit in my garage.

Thanks,
Bill

PS I was pricing the 5.0 V8 (maybe 3.5L EcoBoost)

* This post was edited 01/11/11 10:32pm by an administrator/moderator *


Bill & Terry
Plus our canine kids, Skippy & Peanut
2014 Fleetwood Bounder Classic 30T
2013 Ford Fiesta in tow
Blue Ox base plate
Blue Ox Alpha tow bar
SMI Stay-in-Play aux. brake


ricatic

Home

Senior Member

Joined: 06/25/2009

View Profile


Offline
Posted: 01/11/11 10:18pm Link  |  Print  |  Notify Moderator

What engine are you looking at? The 2011 Ford 6.7 diesel SRW trucks are not available with axle ratio's above 3.55. They do not need higher ratios either. Diesel dually's start at 3.73 gearing. SRW gas powered trucks with the 6.2 can be had with 4.10 or 4.30 gears.

Regards


Ricatic
Debbie and Savannah the Wonderdachsund
2009 Big Horn 3055RL
2006 Chevrolet Silverado 3500 Dually LTX with the Gold Standard LBZ Engine and Allison Transmission
2011 F350 Lariat SRW CC SB 4WD 6.7 Diesel POS Gone Bye Bye

blt2ski

Kirkland, Wa

Moderator

Joined: 03/15/2001

View Profile


Offline
Posted: 01/11/11 10:41pm Link  |  Print  |  Notify Moderator

Reality is, with the newer 6sp transmissions, a 3.55 will be better than 4sp autos with 4.10's! So get the lowest AR you can. Reality is, 3.55 to a 3.73 is not enough to worry about. You could change the 3.55 setup to an effective 3.73 by buying tires that are an inch in diam smaller than stock! Unless you have a really small hp/torque motor, not enough to notice in most cases from experience.

Ricatic, from the engine choices posted after your post, appears to be looking at F150's.

Marty


92 Navistar dump truck, 7.3L 7 sp, 4.33 gears with a Detroit no spin
00 Chev C2500, V5700, 4L80E, 4.10, base truck, no options!
92 Red-e-haul 12K equipment trailer

Check RV.Net Blogs at: blog.rv.net

Fordlover

Spring, Texas

Senior Member

Joined: 12/27/2005

View Profile


Offline
Posted: 01/11/11 10:55pm Link  |  Print  |  Notify Moderator

B&TA wrote:

I see all this info about the 3.73 axle being best for towing, but...




I believe Ford is offering 3.15, 3.31, 3.55, 3.73 on the F-150. The 3.73's are only available on the Max Tow package. The Max Tow package is not availabe on the 5.0 engine, you must order the Ecoboost engine or the 6.2 liter for the Max tow, which has the 11,000+ tow rating. I believe the tow rating on the 5.0 liter tops out just under 10,000 lbs.


02 Ford Explorer 4.6 V8 4x4, prodigy and equalizer
07 Crossroads Sunset Trail ST19CK
07 Infiniti G35 Sport 6 speed, Hauls @$$
and no payments

BenK

SF BayArea

Senior Member

Joined: 04/18/2002

View Profile



Posted: 01/11/11 11:00pm Link  |  Print  |  Notify Moderator

First here are the basics or laws of physics on gear ratio

It has to do with the ring gear (larger and being driven) and the pinion
(small and driver of the ring gear). So the pinion turns 3.55 times to
one turn of the ring gear for a 3.55 gear ratio and 3.73 times to one
turn for the 3.73 ratio and 4.1 times for the 4.1 ratio and so on.

Then for discussions stake, use 100 ft/lbs of torque on the drive shaft,
which turns the pinion gear, which then drives the ring gear (both
inside the diff pumpkin).

With a 3.55 gear ratio, that 100 ft/lbs become 355 ft/lbs of torque and
with a 3.73 gear ratio, that then becomes 373 ft/lbs and with a 4.1 gear
ratio that then becomes 410 ft/lbs and so on

Moving the TV and the trailer takes power. The faster you wish to
accelerate, the more power needed. The faster you wish to go the more
power is needed.

The transmission also has gears and ratios that go along with it. So
there is torque multiplication there too. It is between the engine and
differential, so it's ratios factor the engine torque, which then is
factored by the differential ratio.

A 3.55 vs 3.73 is just 0.18 difference and is small to most setups
unless you are at the hairy edge and that makes the difference. If so,
they you also have other issues to deal with.


-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...

SoCalDesertRider

Arizona desert

Senior Member

Joined: 12/14/2003

View Profile



Posted: 01/11/11 11:53pm Link  |  Print  |  Notify Moderator

Ford's witholding gear ratios for stupid reasons is a real pisser. What the heck does wheel base length have to do with axle ratio? Nothing at all.

Buy the truck you want then take it to the driveline shop and have them change the axle ratio to whatever one works best for your intended use.


05E350 6.0PSD
97F350DRW 7.3PSD 4x4 4.10 11' flatbed
98Ranger
69Bronco ATC250R CR500
20' BigTex flatbed carhauler
Callen Camper

92F350 CrewCab 4x4 351/C6
B&W TurnoverBall, Curt Magnum V
HD Springs Bilsteins,
285/75-16E BFG AT on 16x8 Stocktons
4.56's & LockRite rear

brianjw

Here and There

Senior Member

Joined: 10/25/2009

View Profile



Posted: 01/12/11 12:37am Link  |  Print  |  Notify Moderator

I agree that 3.55s should be very capable with smaller tires on the 2wd truck, and the six speed transmissions.

However, it would be nice if they offered all options on all trucks. Ford is infamous for screwing up their ordering system with "packages" and options that can only be ordered on some models. Fortunately for you, re-gearing a truck with only one axle is not that expensive. Plus it gives you a great opportunity to get a good limited slip or locking differential.


2006 F150 SuperCrew FX4 - Bilsteins, Hellwig sway bar, Firestone air bags, BFG KM2s, 4.56 gears, F&R lockers, Torklifts w/ Fastguns
2011 Travel Lite 700


TXiceman

Full Time RVer

Senior Member

Joined: 11/17/2000

View Profile



Good Sam RV Club Member

Offline
Posted: 01/12/11 06:21am Link  |  Print  |  Notify Moderator

The lower gears on the new 6 speeds are not much if any lower. The extra two gears are generally double over drives. Point is I would still want 3.73 or 4.10 gears for towing. You want to let the rar axle handle the torque amplification, not the transmission.

They are pushing the 3.55 axles to get the mileage numbers up, never mind the towing.


Amateur Radio Operator.
2013 HitchHiker 38RLRSB Champagne, toted with a 2012, F350, 6.7L PSD, Crewcab, dually. 3.73 axle, Full Time RVer.
Travel with a standard schnauzer and a Timneh African Gray parrot

APT

SE Michigan

Senior Member

Joined: 06/09/2010

View Profile



Posted: 01/12/11 06:22am Link  |  Print  |  Notify Moderator

The axle ratio is not exclusively important. You need to know the transmission gear ratios too. The F-150 6-spd with 3.55 axle ration would be better than the previous 4-spd and 4.56 gears. GM only offers 3.42 axle ratio with similar transmission gearing with its 5.3L. 3.55 is fine. That said, I highly recommend 3.73 and if you want an FX4 with 20" wheels, might as well get the 4.10. Higher is better in almost every gas engined truck I can think of. Fuel economy difference between 3.55 and 3.73 is unmeasurable. May examples have I heard of people going to shorter axles and getting better fuel economy, especially towing.

A little expansion on what Fordlover wrote. The max tow package gets you the 3.73 axle, but forces you to get the EB or 6.2L, depending on trim level. That package is worth every penny for TT owners as it gets 300-400 pounds more payload with a higher GVWR. Highly recommend it for the F-150. It also includes the big, expanding mirrors, brake controller, and upgraded trans cooler, Selectshift trans control for like $600. The EB is also worth researching and driving when they hit the lots probably next month. Better than diesel torque curve (at least 380lb-ft 1700-5000rpm), perfect for towing.

Now that I look at it, I can build and price a 2WD XLT Supercab 6.5' bed 5.0L non max tow package truck with the 3.73LS axle. But I still recommend the EB and max tow package.

ricatic

Home

Senior Member

Joined: 06/25/2009

View Profile


Offline
Posted: 01/12/11 06:36am Link  |  Print  |  Notify Moderator

brianjw wrote:

I agree that 3.55s should be very capable with smaller tires on the 2wd truck, and the six speed transmissions.

However, it would be nice if they offered all options on all trucks. Ford is infamous for screwing up their ordering system with "packages" and options that can only be ordered on some models. Fortunately for you, re-gearing a truck with only one axle is not that expensive. Plus it gives you a great opportunity to get a good limited slip or locking differential.


What has Ford screwed up here? Just listen to the owners of the new Ford drive lines and you will soon understand that these axle ratios work perfectly with the engine/transmission combination's now available. No one is running out and buying smaller tires to raise ratio's or spending money on different ring and pinion setups. The electronic rear lockers have been very effective. You will not need to run out and get a better one. The new power trains have made better fuel economy and heavier tow ratings possible. Old thinking dies hard but the new trucks have proven to perform as designed. Just ask someone who actually owns one...

Regards

This Topic Is Closed  |  Print Topic  |  Post New Topic  | 
Page of 5  
Next

Open Roads Forum  >  Tow Vehicles

 > 3.55 vs 3.73 rear end question
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:

© 2014 Woodalls | Terms & Conditions | PRIVACY POLICY | YOUR PRIVACY RIGHTS