2011RBLariat

I would like to buy a new Travel Trailer the dry weight of the trailer is 6400lb the gvwr would be about 8400lb of course I would not be pulling with water tanks full. My 2011 ford 150 Lariat max towing is 8000lbs with a 3.55 rear end 5.0l engine 1500lb payload. Can the ratio of the rear end be upgraded to a 3.73 rear end by just changing the gears, are will the whole rear end have to be change. The same truck with 3.73 rear end can pull 9400lbs according to the towing guide.

acadianbob

You would just change the gears but that is a lot of expense. You can accomplish virtually the same thing by towing in 5th.

You should be more concerned about your payload capacity than the overall weight of the trailer and your gearing. You may find that the weight of your passengers (including you), stuff you have in the bed of the truck, and the tongue weight of your trailer exceed the payload capacity of your truck.

Wudwork

Acadianbob has it right, your limitation is the payload. We all have to learn this, some the hard way. The 6500lb trailer will likely put 10% or perhaps 675lbs on the truck back axle (tongue weight). Add to that you and wifie (350lbs?) you are now close to 1000 lbs on the truck payload with a MAX of 500 more to go. Thats tight. We all believe in margins and try our best to stay below the payload limit.

Also, about towing dry; not always. While we never leave home wet, we dry camp quite a bit and sometimes there is no dump station until we drive out maybe 20 miles. Those are 20 miles with WET black and perhaps gray tanks. Those weights cannot be ignored.

Did you weigh the trailer at a local landscaping type place? We were sadly shocked at the true dry weight, it was 350 lbs more than sticker.

Here is something to consider: lets say your trailer "camping ready" is 6800 lbs. You have some weight you can add to trailer axle before it approaches its limit (with margin). That could be weight you don't put in your truck bed. So consider spreading the load over ALL your axles and certainly tow with a Weight Distribution Hitch (WDH) that includes sway control.

11screw50

With a payload of 1500# and 13% tongue weight (and assuming loaded TT weighs in at 1000# more than 'dry weight'), that is almost 1000# gone right from the start. Add 350# for passengers and you're down to 150# available (and that is easy to chew through with just miscellaneous crap in the truck).

I do think it needs to be pointed out that the 10% referenced above with regard to tongue weight is generally considered the lowest you would want to be (not necessarily possible or desirable). The typical range is 10-15% with 13% often being used when the true percentage is not known.

As for your 350# higher than sticker, if you mean the brochure, those are without options and without LP or battery.

Not sure it is worth regearing from 3.55 to 3.73 since even though in theory you gain towing capacity, you won't be able to use it because you will reach payload far before you even reach your current tow capacity. The 3.73's should do better on hills though...

Dirttracker18

Downshifting your transmission to 5th gear is not virtually the same as having deeper rear gears.

The deeper gears put less strain on the drivetrain in front of it. Downshifting does not accomplish the same thing.

acadianbob

What you say is true but is splitting hairs I think. What you say would be true on from the output shaft of the transmission through the rear axle. But the difference between 3.55 and 3.73 is inconsequential; especially since the truck is within its total weight limits. What would happen is that the engine would run at an elevated rpm in 5th that would be fairly equivalent to 6th gear with a deeper rear end.

Since this happens all of the time, I don't think it is a factor. Virtually every manufacturer provides for lockout of higher gears. If it was actually going to be a problem, manufacturers would put in the deeper gears.

Dirttracker18

I never said it was an issue or different gears were needed.

What I did say is that you cannot compared downshifting to deeper gears. They are not performing the same function.

Given your further statement of locking out 6th, the argument becomes moot as a truck with deeper gears would be in 5th either way but the one with deeper gears would have better access to it's power.

Boulevard

It is easier to change out the whole differential not to mention faster and cleaner.

You will not notice any difference between a 3.55 and a 3.73 rear end despite what FORD puts in print. Check your gearing charts to confirm a 100 rpm difference between the 2 gear sets...all gears, any speed. Its just not enough of a change. Please do not ask me why FORD changes is tow ratings so drastically because I am not getting back into that argument.

Changing your gear set will not allow you to legally tow more than rated capacity but it will allow the truck too tow its rated capacity easier (if the gear change is large enough). Either way you really are still stuck with the door sticker. Here is another argument that I do not wish to get back into.

Bottom line..stick with the 3.55's.

I have a 2013 SC with the 5.0, the 3.55 gear set and a 1440 lb payload. I tow a 6000 lb travel trailer with absolutely no problem. I would give your truck a chance to impress you and then start thinking about modifications.

Wudwork

VERY well said. +1 for new sticky.

Dirttracker18

To be specific, 100 rpm does make a difference when towing and that is why there is an increase in ratings.

Note the chart below, during the most critical and normally used RPM area (1500 - 2500) the torque curve is very steep. This means that a 100 RPM difference means a significant jump in usable torque. Make no mistake that 100 RPM difference will be useful when towing or hauling any load. You are talking about a 20 to 30 ft/lb difference in torque in the most useful RPM ranges at all times.




This does not even take into consideration the torque multiplier effect of deeper gears.

Do you NEED deeper gears, no it will work and it will tow reasonably well.

However to say that there is no significant difference is misleading and misunderstood.

Why does FORD and all other manufacturers do that? Simple, math. You cannot argue with the math of where you are in the torque curve and what that means for moving mass. Essentially you are using a longer lever.