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01-28-2017, 08:42 AM
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#1
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Member
Join Date: Dec 2016
Posts: 85
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Rear Axle Gear Ratios - Best for Towing
Getting confused about rear axle gear ratios and what is the best for full-time towing a trailer or fifth wheel. 4.10? 3.73?
So, what do you think?
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01-28-2017, 08:45 AM
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#2
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Senior Member
Join Date: Oct 2016
Posts: 351
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Quote:
Originally Posted by CascadeBob
Getting confused about rear axle gear ratios and what is the best for full-time towing a trailer or fifth wheel. 4.10? 3.73?
So, what do you think?
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I am no expert but I pull a 16.5k, 38fter with a 6.7 Ford with 3.55 gears just fine.
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01-28-2017, 10:13 AM
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#3
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Senior Member
Join Date: Oct 2015
Posts: 362
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Not apples to apples, but my observations.
My truck is stock 2013 Cummins 3.42 with 13,500 GVWR bumper pull TH.
My fathers is tuned, deleted, 4.10 DRW with 17k 5th wheel TH.
On the longer and steeper grades letting the transmission in T/H do the shifting and cruise set as I would start to bog down on he would gain on me until my truck downshifted into 5th then I'd start to pull away until his shifted and by the top of the hill our spacing was the same as when we started.
I locked out 6th, and he would be playing catch up.
With these 6 speed trans with double overdrive and massive power from the current diesel offerings the gear ratio isn't as important as in a naturally aspirated gas rig, in which case go as numerically high as you can for best towing performance.
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01-28-2017, 10:30 AM
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#4
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Senior Member
Monaco Owners Club
Join Date: May 2012
Location: DFW, Tex-US
Posts: 6,196
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I think:
Don't overthink it
But towing with what engine and what load ?!?
anything can tow 5k lbs...
just buy the truck you want that will do the job and
don't expend the money to change what the engineers designed it for
our 2012 and 2013 6.7 fords with 3.55's towed heavy, HEAVY 5'ers without a whimper...
But, my truck's were not just full time pullers so that's why the 3.55's worked for me... if yours is never unhooked from 16k+ lbs, then consider shorter gears, but not a show stopper either way.
__________________
'11 Monaco Diplomat 43DFT RR10R pushed by a '14 Jeep Wrangler JKU. History.. 5'ers: 13 Redwood 38gk(junk!), 11 MVP Destiny, Open Range TT, Winn LeSharo, C's, popups, vans, tents...
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01-28-2017, 11:34 AM
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#5
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Member
Join Date: Aug 2011
Location: Florida
Posts: 44
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Rear Axle Gear Ratios - Best for Towing
It largely depends on the truck and the load you plan to pull with it. If you're talking a new diesel with a 6+ speed transmission, then a 3.55 or 3.73 gear truck may be fine, but a gasser with an 8 speed may only need a 3.42, or a 3.73 with a 6 speed. Basically nearly all trucks have different tow capacities depending on what gear and transmission they come equipped with.
Figure out the weight of your trailer and your expected payload, then look at the charts for tow capacities and payloads then pick the truck configuration that is more than what you need, but not way over, unless you're at the top of course. It's always better to have more truck than you need. Though breaking even is possible, it's generally safer to have more truck than trailer.
If you just want a generic answer. Then the truck with the biggest engine, the most transmission gears, and the higher numerical gear ratio is generally going to be the best tow vehicle.
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01-28-2017, 03:34 PM
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#6
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Senior Member
Join Date: Aug 2012
Posts: 1,580
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A diesel engine operates at a much lower RPM than a gas engine, when discussing gear ratios you don't compare diesel and gas.
Since modern transmissions have overdrive in the top gears, you multiply the top gear times the axle gear to get the real result.
Tire diameter is another big factor that needs to be considered.
Just throwing out your favorite numbers is not useful.
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01-28-2017, 04:44 PM
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#7
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Senior Member
Join Date: Aug 2015
Location: Phoenix, Oregon
Posts: 2,207
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Do a search for a rpm-mph calculator. Here is a link to one Engine RPM Calculator There are many of them. Play with numbers until you find a gearing combination that works for you. I have always looked for something that would provide a desired top speed somewhere near the peak torque rpm of the engine.
Best of luck.
Steve
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01-28-2017, 05:22 PM
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#8
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Junior Member
Join Date: Jan 2017
Location: Salfordville
Posts: 16
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It depends on the torque curve of the engine and how the transmission and torque converter are set up. Today's trucks are different. I owned a 2011 F350 6.7 power stroke with 3.55's. I pulled 11k travel trailer- on level ground it pulled veery well. The power stroke has loads of torque down low around 1400 rpms. I was able to keep the trans in 6th (high) as long as I kept going at 70mph cruising. If I hit slightest grade it would go down to 5th. The downside was if I got into traffic or stuck behind slower vehicle and dropped below 65, the trans would be shifting up, down. The 3.55's just weren't good for me towing 11k without the trans doing a lot of shifting. I just got a 2016 F350 dully with power stroke 3.73's, now this is the perfect set up. I can run down to 60mph then back to crushing 65-70 without annoying shifting.
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01-28-2017, 06:55 PM
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#9
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Senior Member
Join Date: Oct 2015
Posts: 362
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Quote:
Originally Posted by engineer78
It depends on the torque curve of the engine and how the transmission and torque converter are set up. Today's trucks are different. I owned a 2011 F350 6.7 power stroke with 3.55's. I pulled 11k travel trailer- on level ground it pulled veery well. The power stroke has loads of torque down low around 1400 rpms. I was able to keep the trans in 6th (high) as long as I kept going at 70mph cruising. If I hit slightest grade it would go down to 5th. The downside was if I got into traffic or stuck behind slower vehicle and dropped below 65, the trans would be shifting up, down. The 3.55's just weren't good for me towing 11k without the trans doing a lot of shifting. I just got a 2016 F350 dully with power stroke 3.73's, now this is the perfect set up. I can run down to 60mph then back to crushing 65-70 without annoying shifting.
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Lock out 6th, problem solved and probably get a little better mpg too.
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01-28-2017, 07:06 PM
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#10
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Senior Member
Join Date: Dec 2012
Location: Oregon
Posts: 6,596
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I have 3.73's and a CTD. Under 60mph I leave it in 5th. If I run up to 65mph then I'll shift it to 6th. I find 6th at 50-60mph wants to shift down often enough that I just stic it in 5th. Last trip we took I left it in 5th probably 70% of the time and noticed no change in mpg. I've got 32" tires and my CTD turns 1800-2000rpm running 50-60mph in 5th. Perfect rpm for hilly and mountainous roads. I'm also towing light at around only 9000lbs.
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01-29-2017, 07:22 AM
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#11
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Member
Join Date: Dec 2016
Posts: 85
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Whew! Yep - complicated. I did purposely post a g3eneric question to avoid the conversation focusing on truck brands or other distractions, but - since many of you ask:
We haven't bought our set up yet, but we're pretty sure we'll set ourselves up in the following:
Towing vehicle: Used Silverado 3500 or maybe Ford 350, 6.6 or 6.4 diesel, crew cab, 6-speed tranny, 4X4, standard (6') bed, between 2008 - 2015 vintage truck.
Fifth Wheel: Northwood Fox Mountain 235RLS, gross vehicle wt (loaded) 11,500 lbs, hitch wt (dry) 1,375 lbs.
A one-ton truck is probably way more than we need for that fifth wheel, but we may trade up fivers in the future and want to stay far below truck towing capacities since we plan to boondock a lot (up those steep, wash-board BLM and Forest Service roads).
Still confused about the actual axle ratios. Is it the smaller the gear-ratio number the more revolutions for the engine? So is a 3.73 rear end geared "lower" to haul more weight, all other things being equal?
And is the downside to lower gears that they spin faster at higher speeds (producing a higher risk of heating up and burning out)?
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01-29-2017, 07:36 AM
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#12
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Senior Member
Join Date: Aug 2012
Posts: 1,580
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Quote:
Originally Posted by CascadeBob
Still confused about the actual axle ratios. Is it the smaller the gear-ratio number the more revolutions for the engine? So is a 3.73 rear end geared "lower" to haul more weight, all other things being equal?
And is the downside to lower gears that they spin faster at higher speeds (producing a higher risk of heating up and burning out)?
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You are correct on the axle ratio question.
Lower gears will allow the engine to spin faster at all times. You are incorrect on the "heating up" question, the opposite is true. The lower gears are better for the transmission as well.
Skip the 6.4, and go to a 6.7 built after March 2011, if you decide on a Ford.
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01-29-2017, 08:07 AM
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#13
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Senior Member
Join Date: Feb 2009
Location: Ca
Posts: 1,076
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Why a 6' bed on a 3500? Just curious.....My 3500 6.7 CTD has 3.73 gears.
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01-29-2017, 08:08 AM
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#14
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Senior Member
Join Date: Oct 2015
Posts: 362
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Quote:
Originally Posted by CascadeBob
...or 6.4 diesel...
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NO. STAY AWAY From 6.4.
Quote:
Still confused about the actual axle ratios. Is it the smaller the gear-ratio number the more revolutions for the engine? So is a 3.73 rear end geared "lower" to haul more weight, all other things being equal?
And is the downside to lower gears that they spin faster at higher speeds (producing a higher risk of heating up and burning out)?
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The higher the numeric number, the lower it is geared. 4.10:1 is lower geared than 3.73:1. 4.10 will tow more with less effort.
The only downside to worry about is more engine revs and burning more fuel at the same speeds.
With the smaller fifth wheel you are looking at a higher geared rig will have no problem towing it.
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