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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.
True...but it is not 100 rpm difference at any speed as he claimed. The 3.55's will be 5% lower, period. At 2,000 rpm, sure, it's 100 rpm difference. At 3,000 rpm, it is a 150 rpm difference. I guess, given the curve, the torque differential probably stays close to the same even as the rpm gap grows though...
As for the ratings. Here is one for you: 2011-14 SCrew, 145" wb, 4x2. GCVWR's are: 13,500# (3.31), 13,500# (3.55) and 15,100 (3.73). Based on the curves and differences in mechanical advantage provided by the gears, there is no way the 3.31's and 3.55's should carry the same rating.
FWIW, it is similar with the same configuration (except 4x4) for the 2015's going from 3.31's to 3.55's gains you 100#, going from 3.55's to 3.73's gains you 1800#. Oddly enough, with a SCrew 4x2 you gain 1000# going from 3.31's to 3.55's and 3.73's are not available.
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.
You'll be overloaded over the payload capacity of your F-150. You'll run out of payload capacity long before you run out of tow rating.
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.
To change gear ratio in the differential, all you change is the ring gear and pinion. If the truck is a 4x4, you have to change the ring gear and pinion in both front and rear differentials, but based on your tow rating yours is a SuperCrew 4x2 so there is no front differential.
Or if you can find a wrecked F-150 in a bone yard that has 3.73 ratio, you can swap out the entire third member for probably less money than changing only the ring gear and pinion. Any decent shade-tree mechanic can swap out the third member, but it requires an expert technician to tear into a differential and change the ring gear and pinion, and put it together exactly right so there is no vibration or other ill effects of a poor job of installing the new gears.
The same truck with 3.73 rear end can pull 9400lbs according to the towing guide.
Don't misinterpret those tow ratings. Notice that word "maximum". In order to tow a TT that grosses 9,400 pounds, the wet and loaded F-150 SuperCrew 4x2 with driver, passenger(s), tools, full tank of gas, and WD hitch head mounted in the receiver would have to weigh only (14,900 GCWR minus 9,400 trailer weight = ) 5,500 pounds. Weigh your truck and you'll see that it weighs a lot more than 5,500 with full tank of gas, driver, any passengers you plan to haul when towing, tools and a jack, and the WD hitch head.
Because your limiter as to trailer weight you can tow without being overloaded is the GVWR and payload capacity of your F-150, and not the GCWR and tow rating, in order to determine the max trailer weight you can tow without being overloaded you need to weigh the wet and loaded F-150.
Load it with everyone and everything that will be in it when towing, including tools, jack and jack base for changing a trailer tire. Drive to a truck stop that has a CAT scale, fill up with gas and weigh the wet and loaded tow vehicle. Subtract the weight of the tow vehicle from the GVWR of the tow vehicle. The answer is the maximum unused payload capacity available for hitch weight.
Divide that maximum unused payload capacity available for hitch weight by 0.13 and the answer is the maximum GVWR of any tandem-axle travel trailer you want to consider. Guaranteed, it will be a lot less than 8,000 pounds, regardless of your axle ratio.
So you don't need to change the gear ratio in your F-150. You need to either buy a lot lighter trailer, or else trade for more tow vehicle that has adequate payload capacity for the hitch weight of your trailer. If you travel with very little weight in the F-150, then I'd guess your max trailer weight without being overloaded would be a TT with not more than 6,000 pounds GVWR.
My F-150 Lariat SuperCrew is similar to yours, with 1,566 payload capacity. My TT has GVWR of 5,600 pounds, and it actually weighs 4,870 including 650 pounds of tongue weight when wet and loaded for the road. My tow rating is 8,400 pounds, but I'm overloaded over the GVWR with that 650 pounds of tongue weight. So forgetabout that 8,400 tow rating and realize my real-world tow rating is less than 5,000 pounds.
And don't be surprised if your real-world tow rating is a lot less than 7,000 pounds, and probably less than 6,000 pounds.
Last edited by smokeywren; 02-18-2016 at 09:56 AM.
Not everybody will carry 900lbs of stuff in their truck though. my family and stuff weights about 500lbs. everything else goes in the trailer.
The main thing you should do is make an informed decision. if the GVWR of the trailer is already over your tow rating, it's probably too much trailer for you. I would recommend looking at a lighter one.
02-17-2016, 04:20 PM
