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  #1  
Old 03-12-2008, 02:50 AM
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Going from 3.73 to 4.10??? Tow guys help!

Hello everyone and thanks for reading. My truck '05 Scab 4x4 5.4 8200GVWR and has stock 4.10's and stock 245/70/17's. I did some research and basically when I upgrade my wheel/tire combo to either a 285 or 295/70/17 I will effectively reduce my gearing from 4.10 to 3.81 (285's) or 3.74 (295's) - I will in the future be towing a 6500lb(loaded) toy hauler with sway bars/WD/airbags/BKcontroller and I wanted to hear from guys who tow with either

1) 3.73's stock (how does it do) or
2) upgraded from a 3.73 to a 4.10 (how much improvement did you gain).
3) Do you see a lightly tuned (exhaust/troyer tune) 5.4 w/ 3.73's and proper towing gear having problems with this trailer for trips up to say 300-400 miles one way?
4) How about weights up to say 7k (loaded)

Thanks and have a great day!

Alex

Last edited by 7lug; 03-12-2008 at 03:38 AM.
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  #2  
Old 03-12-2008, 08:53 AM
APT APT is offline
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No one would change gears from 3.73 to 4.10. Not worth it, especially on a 4x4 where gears cost $1000-1500. 3.73 to 4.56, yes!

I'd say either keep near stock tire size/weight or prepare to get 4.88 gears.
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  #3  
Old 03-12-2008, 09:25 AM
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Quote:
Originally Posted by APT
No one would change gears from 3.73 to 4.10. Not worth it, especially on a 4x4 where gears cost $1000-1500. 3.73 to 4.56, yes!

I'd say either keep near stock tire size/weight or prepare to get 4.88 gears.
One of the cheapest ways to upgrade gear ratio (for 2wd guys and me in the past) is to get a used rearend from the wrecking yard with a better ratio - considering that F series trucks have been on top of the sales charts forever, that makes alot of wrecking yard parts available.

And for just a 285 or 295/70/17 - a 4.56 gear will put you over the stock ratio of 4.10's with 245's... that 4.88 is better left to guys with 35's and up IMO
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  #4  
Old 03-12-2008, 11:51 AM
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APT, I think he already has 4.10's. He's saying that when he gets the larger tires, his 'effective' gear ratio will be in the 3.73 range.

7lug, I tow a #5000 TT and have 3.55's and LT265/75/16 tires! About the same height as the 'optional' 265/70/17 tire that was available for my rig in 1997.

I tow fine and I'm pulling around 2300-2500 rpms in third gear going 60-65 mph. My engine seems to like that rpm range. Your '05 is the 3v, so it kinda likes the higher rpms for it's peak numbers, so you might need to let it rev if you want the peak numbers...

If you are looking to tow in OD, then get 4.56's with the new tire size IMO.. But, towing in OD (even with 4.56's) is not going to net you anymore MPG's while towing, just lower your rpms for that time... If you are able to hold OD while towing a #7000 brick for hours on end, then maybe a mpg or two, but not anything you will be able to calculate for a 1000 mile trip (unless it's all done in OD one way, and you go third the other..)

If it was my rig, I'd get the 285's. Keep the stock 4.10's. Tow my #7000 TT in third gear which should put your rpms around 2500-2700 going 60-65 mph. Your 3v should love that rpm range with that load on it...

I get 16 mpg in OD running empty. I get 10 mpg towing my trailer in third. I get 10 mpg if I let it go into OD every now and then... $1500 will buy a lot of gas, even at $4.00 gallon for when you are towing, so....

Good luck!

Mitch
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2013 F150 XLT 4x4 SuperCab EgoBoost Max Tow 3.73 gears OEM 20" wheels.

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  #5  
Old 03-12-2008, 12:10 PM
APT APT is offline
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Quote:
Originally Posted by 7lug
One of the cheapest ways to upgrade gear ratio (for 2wd guys and me in the past) is to get a used rearend from the wrecking yard with a better ratio - considering that F series trucks have been on top of the sales charts forever, that makes alot of wrecking yard parts available.
2 points. You have 4wd and You already have the shortest gear in your F-150 than was offered, so those "cheap upgrades are not gonn happen. 4WD gear changes = front and rear differentials. More than twice the cost of 2WD rear only and more than twice the labor if you don't do it yourself.

Quote:
And for just a 285 or 295/70/17 - a 4.56 gear will put you over the stock ratio of 4.10's with 245's... that 4.88 is better left to guys with 35's and up IMO
People with stock 3.73 gears and 32" tires (think most 4WD Supercrews) that upgrade tires to 35" benefit by going to 4.56 gears. Every account of people who did it increase acceleration as well as fuel economy. That's a 22% gear reduction to compensate for only a 6% tire size increase. That's because those 35" tires (and most 33" tires) are heavy, like 55-60 pounds vs. 40-42. Increased tire/wheel weight takes more to move than throwing 100 pounds in your truck bed. Since you already have 4.10 gears with relatively tiny tires (30.5"), you need more than the 11% gearing improvement (4.10->4.56) to recover from the 7-9% larger tires you are talking about getting. That is, to at least keep near stock acceleration, towing or not.

I have heavy 33" tires and 3.73 gears and would love 4.56 gears instead. I currently use my truck for commuting 65 miles a day and get 12mpg average. While I have towed well over my ratings, my typical trailer weighs 2500 pounds and keeping overdrive locked up is difficult on anything but flat highways.

But hey, some people on hear with 25" tires and 6000# vehicles tow 7000 pounds and don't complain. Everyone's performance expectations are different.
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  #6  
Old 03-12-2008, 02:02 PM
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Quote:
Originally Posted by MitchF150
APT, I think he already has 4.10's. He's saying that when he gets the larger tires, his 'effective' gear ratio will be in the 3.73 range.

7lug, I tow a #5000 TT and have 3.55's and LT265/75/16 tires! About the same height as the 'optional' 265/70/17 tire that was available for my rig in 1997.

I tow fine and I'm pulling around 2300-2500 rpms in third gear going 60-65 mph. My engine seems to like that rpm range. Your '05 is the 3v, so it kinda likes the higher rpms for it's peak numbers, so you might need to let it rev if you want the peak numbers...

If you are looking to tow in OD, then get 4.56's with the new tire size IMO.. But, towing in OD (even with 4.56's) is not going to net you anymore MPG's while towing, just lower your rpms for that time... If you are able to hold OD while towing a #7000 brick for hours on end, then maybe a mpg or two, but not anything you will be able to calculate for a 1000 mile trip (unless it's all done in OD one way, and you go third the other..)

If it was my rig, I'd get the 285's. Keep the stock 4.10's. Tow my #7000 TT in third gear which should put your rpms around 2500-2700 going 60-65 mph. Your 3v should love that rpm range with that load on it...

I get 16 mpg in OD running empty. I get 10 mpg towing my trailer in third. I get 10 mpg if I let it go into OD every now and then... $1500 will buy a lot of gas, even at $4.00 gallon for when you are towing, so....

Good luck!

Mitch
Thanks Mitch - The more I think about it the more I am leaning towards the 285's as you mentioned, I just want to make sure the truck doesn't look like it's missing too much tire. With a 163" WB, hardcore wheeling isn't in my future anyways so again, 285's will work well, and again...I appreciate your feedback

Last edited by 7lug; 03-12-2008 at 02:14 PM.
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  #7  
Old 03-12-2008, 02:14 PM
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Quote:
Originally Posted by APT
2 points. You have 4wd and You already have the shortest gear in your F-150 than was offered, so those "cheap upgrades are not gonn happen. 4WD gear changes = front and rear differentials. More than twice the cost of 2WD rear only and more than twice the labor if you don't do it yourself.



People with stock 3.73 gears and 32" tires (think most 4WD Supercrews) that upgrade tires to 35" benefit by going to 4.56 gears. Every account of people who did it increase acceleration as well as fuel economy. That's a 22% gear reduction to compensate for only a 6% tire size increase. That's because those 35" tires (and most 33" tires) are heavy, like 55-60 pounds vs. 40-42. Increased tire/wheel weight takes more to move than throwing 100 pounds in your truck bed. Since you already have 4.10 gears with relatively tiny tires (30.5"), you need more than the 11% gearing improvement (4.10->4.56) to recover from the 7-9% larger tires you are talking about getting. That is, to at least keep near stock acceleration, towing or not.

I have heavy 33" tires and 3.73 gears and would love 4.56 gears instead. I currently use my truck for commuting 65 miles a day and get 12mpg average. While I have towed well over my ratings, my typical trailer weighs 2500 pounds and keeping overdrive locked up is difficult on anything but flat highways.

But hey, some people on hear with 25" tires and 6000# vehicles tow 7000 pounds and don't complain. Everyone's performance expectations are different.
Apt - Thank you for your feedback, I was only referencing the 2wd analogy as it may apply to members in our forum who own 2wd's and have done the rear-end swap I have mentioned and how it affected their performance. I myself did it on my 2wd F150 many years ago when Twin I-Beam suspension ruled the world...

I very much so understand the concept of unsprung weight and it's affect on performance in every aspect from acceleration to braking (both distance and wear) to handling etc, and you're right. I failed to take that into consideration when simply calculating ratios for performance, so thanks for reminding me. Again, I will probably go with the 285's for both gearing and weight issues when upgrading as I do not want to regear the diffs just to tow my trailer less than 6-8x a year. Thanks again bud...

Last edited by 7lug; 03-12-2008 at 02:17 PM.
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  #8  
Old 03-12-2008, 10:50 PM
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I have an 05 Screw with 5.4, 3.73. I tow a 6000 lb 32 foot lightweight hardside trailer. Tires are 285/65R18 6 ply (C) Goodyear ATS. When towing I normally have bikes, firewood, kids, dog, spouse and any thing else that we forgot to pack into the trailer aboard the truck. The truck does fine. I can leave it in OD on flat highways, it never seems overworked. Those tires are 32" by the way. I think your pulling power will be fine. Just set up your anti sway and trailer tongue weight correctly and you'll be good. I work in the auto repair business and I don't do engine mods, so my truck is stock except for some gauges and better fluids.
BTW I am against air bags because they defeat the purpose of weight distributing hitches, with bags you can hang a lot of weight off the back end of your truck and potentially create a fulcrum at the rear axle, not good to take weight off the steering axle. WD, is best. Read about it in www.rv.net in the hitch setup posts. A properly set anti sway hitch is very satisfying going down the highway on a weekend in traffic.

Last edited by NHguy; 03-12-2008 at 11:00 PM.
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Old 03-12-2008, 10:50 PM


 
 
 
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