Thanks, As I recall, our '92 Aerostar owner's manual limits trailer weight to 2000 lbs. I wonder why the older Aerostar has a better tow weight rating. I wouldn't think the LSD could be the difference.

 

TallPaul, the wind resistance increases with the square of the speed increase. Double the speed, resistance increases 4 fold. (2 squared is 4) A ten percent increase in speed increases resistance 21% (1.1 squared is 1.21, the 1.1 represents 110% of the original speed you're comparing to, the 1.21 represents 121% of the original resistance) This also applies to any other types of resistance as well. ie. frictional losses in the engine and driveline. This is why slowing an engine down helps with fuel economy. Engine frictional losses account for 12-15% of the fuel burned. (only 25% of it actually produces power) And when you slow the engine down, the front pump in the trans turns a little slower too. (I'm sure frictional losses through the overdrive planetary will offset this some)

 

WOW! Thanks. My calculations show that wind resistance at 70 is about double that at 50. Anyway, that has got to be the killer for high speed trailer towing. I wonder if anybody makes an aerodynamic nosepiece that can be bolted onto the upper half of the front of a travel trailer?

 

I have seen aerodynamic nose pieces on the front of cube vans, so I'm sure there is something out there that will work. I tapered the front of my box trailer to the width of the towing vehicle. It seemed to help some. Also, any gap over 3 or so feet between the tow vehicle and trailer will add drag too. When I modified the front, I closed the gap 2 feet. Your calculations are correct. A 41% increase in speed will double resistance.

 

The 1992 Aerostar sales booklet says that a properly equiped short version can tow up to 4800lb including passengers and cargo in the van.
The extended version a couple hundred pounds less.
This would require the 3.73 gears with the 3.0L and the 3.55 with the 4.0 L but not the tow package which really only throws in LSD and wiring for class III towing. 2000lbs is for the standard rear gears.

 

 

Thanks TurboBill. I will keep the less than 3 ft rule in mind, though now I am towing the trailer with an F150.

Mark P: Wow! My wife's 92 3.0 with 3.73 gear has a rating of 2000 lb and no more frontal area than the van has. I got this from the owners manual. I don't have a sales brochure.
I will note that I had trouble maintaining 65 mph a lot of the time and the chk engine light was on a lot and there was a burny rubbery or oily smell in the cab while on the highway. I suppose you could tow 4800 lbs, but probably not over 55 mph.

 

Turbobill: Now I am curious though about how trailer weight impacts towing as speed increases. I suspect that wind resistance is the major factor and weight, up to a point, is minor. (I still am considering the aerodynamic nosecone for the trailer with the F150 towing it.)

 

How sure are you that you have the 3:73?
Could it have been miss tagged?
Have you chaulked the drive shaft and a tire and counted the turns? 3:73 turns of the drive shaft for every one of the tire? Also are you using the stock tire size? I always tow with overdrive off and have had no problems.
A head wind does effect the power to pull but even driving up pretty good hills into the wind the trailer with the Honda CRX on it in the earlier picture several postings up was never a problem overheating or transmission wise for my 3.0L automatic. I sometimes exceeded 5500lb trailer/tools/car and a passenger and it still never caused a problem even in 90 degree weather on hills. Don't know what to make of your's inability to tow such small loads.

 

>How sure are you that you
>have the 3:73?
Only by the door tag. I guess I should do your method to be sure. I believe it is stock tire size. I also towed with OD off. I do know that my trailer frontal area was too large by the owner's manual. I think you towed better because your rig has less frontal area, thus less wind resistance. I will let you know what I learn about the true rear ratio.

 

MarkP: I checked and the drive shaft turned 3 and 3/4 times for one tire revolution. The tires are exactly the same spec as on the door tag, I believe 215,70,14. Now here is what I don't understand. In the chart in the owner's manual for this think they have two listings for my situation (auto tranny and 3.73 rear): the one with 5,500 GCWR allows towing up to 2,000 lb with no more frontal area than the van; the one with a 7,500 GCWR allows towing up to 5,000 lb with 50 sq ft frontal area; but nowhere does it tell me whether our van is the 5,500 or the 7,500 GCWR. I suspect the 7,500 GCWR would have heavier springs and thus figured I have the 5,500 GCWR since I have the following on the door plate: 5020 GVWR, 2465 front GAWR, 2630 rear GAWR, front axle reserve capacity 0000, and total axle reserve capactiy of TO118. But if the difference in GCWR is only springs and axle strength, then the van should pull the 5,000 lb trailer, except then it makes no sense to limit the 5,500 GCWR version to a smaller frontal area. What gives? I should be able to understand this (after all, I have a Masters Degree :7), but I don't!

 

It has nothing to do with how your van is equiped as long as it has the 3.73 axle.
If the trailer has the same frontal area as the van or larger, you are limited to the lower 2000lbs limit on trailer size.
If the trailer has a smaller frontal area you can go up to the higher 5000lbs on the trailer. But in either case don't go over the 7500lbs. combined weight.

My van has a gvwr of 5120lbs abd gcwr of 8000lbs with the 3.73 and also the 50sqft limit. My trailer as you can see in the picture I posted earlier, had less frontal area then the van.
A small house trailer could be pulled but slower speeds should be observed. Ford doesn't get into that in their trailering guides but General Motors on their trucks and cars does.

I have copies of the 1988, 1991, and 1996 Ford trailering guides and the wording is essentially the same in all three. And my 88 owners guide reads the same as yours. It's all in the axle ratio and frontal area. Small heavy trailers ok. Large frontal area, heavy trailers not ok.

I hope this clears things up a bit.

Mark





>MarkP: I checked and the
>drive shaft turned 3 and
>3/4 times for one tire
>revolution. The tires are
>exactly the same spec as
>on the door tag, I
>believe 215,70,14. Now here
>is what I don't understand.
> In the chart in
>the owner's manual for this
>think they have two listings
>for my situation (auto tranny
>and 3.73 rear): the one
>with 5,500 GCWR allows towing
>up to 2,000 lb with
>no more frontal area than
>the van; the one with
>a 7,500 GCWR allows towing
>up to 5,000 lb with
>50 sq ft frontal area;
>but nowhere does it tell
>me whether our van is
>the 5,500 or the 7,500
>GCWR. I suspect the
>7,500 GCWR would have heavier
>springs and thus figured I
>have the 5,500 GCWR since
>I have the following on
>the door plate: 5020 GVWR,
>2465 front GAWR, 2630 rear
>GAWR, front axle reserve capacity
>0000, and total axle reserve
>capactiy of TO118. But
>if the difference in GCWR
>is only springs and axle
>strength, then the van should
>pull the 5,000 lb trailer,
>except then it makes no
>sense to limit the 5,500
>GCWR version to a smaller
>frontal area. What gives?
> I should be able
>to understand this (after all,
>I have a Masters Degree
>:7), but I don't!

 

If the trailer has the same
>frontal area as the van
>or larger, you are limited
>to the lower 2000lbs limit
>on trailer size.
>If the trailer has a smaller
>frontal area you can go
>up to the higher 5000lbs
>on the trailer. But in
>either case don't go over
>the 7500lbs. combined weight.

That makes perfect sense. I think the van has about 40 sq ft frontal area, whereas my trailer is closer to 50. I guess if I want to always be able to tow at 70+ MPH no matter the wind or hills, then I should get a 460 V8, but if and until then, the Aerostar and 4.9L F150 will tow fine if compensation is made for wind and hills--a small price to pay for better daily driving fuel economy.

 

Aerodynamics is the largest factor in power needed to go down the road.(at highway speeds) I have towed many different trailers with many different types of vehicles and aerodynamics plays the largest role in power needed. It also greatly affects fuel economy. You've probably noticed that the tractor trailers have become much more aerodynamic over the last 15 yrs. Prior to that time, 50% of the fuel burned at 60MPH was to overcome drag. Todays trucks (semis) get 50% better fuel mileage with nearly twice the horsepower. Weight affects acceleration and hillclimbing the greatest. Once up to speed on a level road, it takes little additional power to pull the weigh along.