Towing Formula

Tom Donnelly

Tom Donnelly

New member
I was reading the thread on sway bars and the associated formulas used to calculate projected rates.

Since there are some engineers out there, is there a formula for towing? Looking at wheelbase of the tow vehicle versus length and height of the trailer. Taking into account spring rates of the tow vehicle and other variables. And including proper load distribution.

I was wondering about a more scientific way to discern how much vehicle you need for different trailers.

For example, one trailer place said a 20' enclosed is too much for an f150/1500 series truck. Another said its just right. Athird said with a load leveling hitch and anti sway a 24' could be pulled fine with the long wheelbase.

My Tahoe had hell pulling a 20' enclosed until I figured out a better load distribution and went to tires I could run 55 psi.

Just want to make a better decision this time without just heresay (although experience helps).

Looking at duallys and deisels and such and then enclosed trailers, I really don't want to have 3-4 times as much money in my tow setup as I have in my dang race car. Thats alot of tire money.

Tom
 
There is no substitute for diesel. They come in trucks which, by design, will haul just about anything us amatuer racers can throw at them.

They make even more sense in light of today's gas prices.

Cheers.
 
I am leaning towards a diesel. What I was wondering about is does wheelbase have an effect (ie leverage) and can you calculate that leverage to determine cycling/wagging trailer. The truck I used f150/1500 range didn't have a problem with pulling. It would cycle down-hill. Part of that is due to load distribution but I was wondering about other criteria.

Tom
 
Tom, a properly-loaded trailer should never tail-wag on you.

A wagging trailer is an indication of the load being too far back. The reason most folks have their load too far back is because when it's properly loaded it makes the truck's ass end "sag too much." That's an indication of an inadequately-sized tow vehicle: not enough rear suspension for the job.

A general rule of thumb is to find out the total load you're planning to tow (car and trailer) and take 10% of that value; that will be your tongue weight. Add to that the weight of all the STUFF you're going to put in the back, and that should be the load your truck is rated to carry over the rear axle. Size your truck appropriately.

Also, don't forget about beefed-up equipment in the larger trucks, such as brakes capabilities; a lot of folks under-size their purchase only to find that the truck brakes cannot safely handle the load.

As for length, a longer wheelbase will give you more leverage if things get out of hand, but you're going to load your trailer properly anyway to avoid that. In reality you want length to be able to contain your stuff adequately. Conversely, a smaller wheelbase makes it easier and quicker to back up and make tight turns in reverse with the trailer.

Then you get into other factors, such as power: how much lack of acceleration are you willing to take? Any modern V-8 engine 'will pull' just about any load, but if it's a large load you're going to find yourself acclerating/merging slowly (plan ahead) and slowing down on hills (plan ahead).

Bottom line, you can never go wrong by going as large as you can afford. I'd strongly encourage you to go with a 1-ton chassis and as big an engine as possible; turbo-diesels are the best for torque, unless you like big-block gassers (Chevy 454s, Ford 6.8 V-10, Dodge V-10).

First and foremost, determine your tongue weight and make sure you size the chassis appropriately. Everything else will fall into place from there.
 
I am in the process of setting up my tow vehicle/trialer combination.

It consists of: a 1995 Chevy Caprice Wagon w/the LT1 motor, 260hp/330ft. lb. of torque.

I am building my own single axle trailer, 10' long deck with a 2' beavertial for a totl of 12'. Just right for the CRX.

Total trailer weight with a set of tires and gas cans in the race car will be around 3000lbs.

This is well within the capacity of the wagon, and I have no doubt the wagon will tow it well.

My question is: Is more tonge weight better? I have adjustable Load distributing/sway bars that will allow me to RAISE the rear of the car, if I want. The figures I have read are 10% to 14%, or in my case, 300 to 420 pounds.

Should I aim for 400 pounds and adjust with the bars? I also have the option of airbags in the rear springs to adjust for the load, but I was planning on loading all my usual race weekend stuff in the back, compensating with the airbags, then hooking the trailer up and adjusting the bars to suit. The plan is to be at the same ride height after everything is loaded/hooked up.

I'm lucky, in that I can locate the axle of my trailer whereever I want it. However, once I set the tongue weight, I plan to weld the axle mounts to the trailer, and will have no further adjustability.

Any thoughts??
 
Tom--If you go Diesel, do a lot of research and test driving. There is a significant difference among the Big Three, although all of their engines are great and close in power. The GM(s) ride the best and have the best auto transmissions.
The F-250 rides OK but is a bit of an "aircraft carrier"; the Dodge was a bit too rough on the ride.

Cheers.
 
There are formulae for determining the optimum configuration for a truck, but the salesman at the local pickup place won't have them.

My father retired after many years managing an operation for one of the largest truck equipment firms in the country. We're talking the big stuff, some of it off-road mining trucks the size of a house, or special trucks for the Alaskan oil fields.

You might check with one of the big-rig salespeople if you are curious.

Gregg
 
Thanks. I had suspected load distribution was a major factor. I haven't tried a weight distribution hitch. I had less tail-wag when I had my toolbox and compressor mounted up front and the car further forward.

I really like the new dodge ram dually. But its expensive!!

Is the major difference between a 1/4 ton and one ton the frame or suspension. And can you install the springs/shocks/etc from a junkyard 1 ton onto a 1/4 ton? Or are the frames so less sturdy they fall way short?

I could pick up (no pun intended) a used 1/4 ton cheap, and I was thinking of just installing 1 ton suspension parts. And another thread suggested a load helper bag?

I think GM is using the isuzu diesel and Ford and Dodge are cummings. I like the big blocks but gas prices are outrageous and off-road diesel is even cheaper and easy to get down south.

Greg, you had a 350 van at the ARRC. Were you pulling an enclosed trailer? And could it if you weren't?

Tom
 
<font face=\"Verdana, Arial\" size=\"2\">Is more tongue weight better?</font>
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Generally; the more load your truck/car can take (dependant on its suspension capabilities), the less chances you'll have with tail-wagging. Look at the extreme: semi-truck/trailers. The truck is taking as much load as the trailer wheels are.

And that's a good example of wheelbase extreme, too: short wheelbase for maneuvering, but if it gets out of shape the opportunity for catching it is significantly reduced. It's all a compromise.

Jon, don't forget to keep in mind the load rating of your trailer axle. If you're building that trailer with a 7000-pound rated axle, you're OK with a CRX. However, if you're building it with 3500-pound axles, you might want to consider either a second axle or a beefier single one (just for safety).

<font face=\"Verdana, Arial\" size=\"2\">Should I aim for 400 pounds and adjust with the bars?</font>
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Yes. Adjust your load properly, then add/adjust the load levelers. Those are not intended to counteract improper loading, they're meant to assist with the load placed on the truck/car.

<font face=\"Verdana, Arial\" size=\"2\">Is the major difference between a 1/4 ton and one ton the frame or suspension.</font>
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Tom, it varies by manufacturer, but AFAIK these days most trucks use the same frame and add better suspension, bigger engines, better transmissions, and bigger brakes for a higher rating. They also add things like trans coolers and bigger radiators. You could probably add a 1-ton suspension and brakes to a 1/2 ton truck and be safe, but I suspect in the end you'll spend more money.

<font face=\"Verdana, Arial\" size=\"2\">...GM is using the isuzu diesel and Ford and Dodge are cummings.</font>
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I don't know what GM's Duramax is, but Dodge is definitely using the Cummins 6-cyl while Ford's 7.3 (turbo and non-turbo) is a Navistar. I don't know what the new (2004 and later) Ford 6.0 diesel is; could it be home-grown? Regardless, I've not heard too many nice things about the 6.0 from guys that work on them; I might suggest if you go the Ford route to stick with 2003 or earlier. Ford used the Navistar 6.9 non-turbo ID diesel up through 1989 (?), a 7.3 IDI non-turbo through mid-'94, a TDI 7.3 in a few iterations through 2003, then the 6.0 TDI in 2004.

<font face=\"Verdana, Arial\" size=\"2\">Were you pulling an enclosed trailer? And could it if you weren't?</font>
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I was not, but I could, within reason. It's a 1-ton Ford van (E-350), and the chassis is fully capable of just about anything I could throw at it. My limitation is power; mine's a 1993, which is a Navistar 7.3 non-turbo. It's fine for my single car and all my junk, but for much anything else I'd need more torque. I was able to keep up with the gasser boys all the way down and back, and got 13mpg in the process...

In fact, I'm facing that power problem now: I've got a buddy that has a Spec Miata, and we're looking for a two-car trailer. Ergo, we're looking for a turbodiesel truck. I could turbocharge my van with a Banks kit or similar, but we'll need extra seats and mine's a cargo van. So, we're in the market for an E-350 passenger van with a Powerstroke engine or a V-10 gasser (ack).

Greg


[This message has been edited by grega (edited May 27, 2004).]
 
From what i've been told the frames are not the same...stuff might bolt on,however here at dodge 3/4 ton,1 ton frames are stronger. P.S.our diesel is only 5.9 liter and has to be detuned to help the trans survive!
biggrin.gif
 
If you get a newer Dodge or Ford Diesel, try and get one with a stick--their autos are suspect.

The GM with the Allison auto box is the cat's meow!
 
I've heard in the past that the dodge 2500 uses some of the same front suspension and brakes as the 1500. But with the bigger engine in the 2500, it would go through suspension and brakes very quickly.

This is not from personal experience, just hear say........


------------------
Jeff L
#74 ITB GTi
 
grega - Thanks for the advice. I'll crank that tongue weight right up to the max.

As for the trailer axle, I cleared my design criteria with dexter. It's a 3500 pound axle. If you want to get really picky, you'll find that an axle needs to be rated to carry the weight of the load and the trailer frame, not including the axle and wheels/tires. This, minus the tongue weight. So:

2200 pound load + 800 pound trailer - 250 pound axle - 300 pound tongue weight = 2450 pound load on the axle.

It's a pretty good safety margin, and the number's I've used are conservative.

Any thoughts???

I've tried to make the trailer as light as possible. I originally thought I'd use two axles and 13" tires, but it cost too much, in terms of dollars AND weight. I'm going with 15" wheels and proper trailer tires, rated over 2000lbs each. The challenge right now is to find wheels rated for the job in my 5 on 5" bolt pattern. I ordered the axle to match the car so I only have to carry one spare tire.

Thanks and regards,

Jon
 
I just thought of something important I failed mention yesterday.

In response to Jon's query of "Is more tongue weight better?" I responded 'generally so.' However, that's not totally accurate. What I failed to mention (I was assuming this as common knowledge) is that as you increase the tongue weight, you obviously increase the load on the rear of the truck, however you're also DECREASING the percentage of load on the front wheels due to leverage around the rear axle. In other words, you're lifting up the nose. At extreme levels, this could could lack of steering and braking on the front wheels; not a good thing.

So what happens, then, as you start to tow larger and larger trailer loads you get to a point where you're incapable of keeping sufficient load on the nose of the truck. At that point you need to shift that tongue load forward; the only way to do that is to go to a fifth-wheel trailer.

A "fiver" is one that has the hitch placed in the bed of a pickup truck (or a cutaway van) immediately over the rear axle; it's also known as a "gooseneck" trailer. The point of a fiver is to place that load forward to eliminate the nose lift and improve rear axle traction, plus better distribute the load on the truck. You'll also notice that semis use a very similar system, with their load actually placed FORWARD of the rear axles; both front and rear axles work together to support the tongue weight.

Finally, regardless of which way you go, don't forget to size your hitch properly. Bumper-attached hitches are rarely sufficient for any kind of serious car hauling; you'll want a frame-mounted Class III or IV receiver.

So, it's a big game of compromise, between gross trailer weight, balance, tongue weight, hitch type, and truck sizing. Bigger is always better, but it's also almost always more expensive, too...

Ah, if money were no object...
 
Just to add minor details...

The Chevy Duramax is an Isuzu.
The 6.0 Ford is a Navistar/International.

6.0 Fords were available in 2003; I belive they did the 7.3 for 4 months or so, then switched over. My '03 Excursion has a 6.0, plus the new 5-speed TorqShift tranny.

Haven't heard anyting bad about that particular tranny yet....

Jarrod
 
One other point to ponder. Those that don't want a 5th wheel, by all means use the load equalizing hitch, aka...torsion bars. The reason being, the bars are designed to place the tongue weight over the rear axle as opposed to the hitch. That is why you can raise the back of the tow vehicle with the bars.

------------------
Chuck Baader
E30 ITA under construction
Alabama Region Divisional Registrar
 
Boy did that hit the nail on the head..

If money were no object...

I'm shot for the day.

Porsche's..BMW's..dually...motorhome..
dyno...shock dyno..machine shop....
full sponsorship....
...TV show...Hooter's girls...

back to reality
 
Originally posted by Tom Donnelly:
...I'm shot for the day.

Porsche's..BMW's..dually...motorhome..
dyno...shock dyno..machine shop....
full sponsorship....
...TV show...Hooter's girls...

back to reality
Click to expand...

C'mon Tom, don't get discouraged. Rumor has it that one of the NER guys is trying to collect Hooter's girls as hot tub attendants for the first annual IT.com shindig at the 2004 ARRC, so you can check that off the list.

Gregg
 
<font face=\"Verdana, Arial\" size=\"2\">...use the load equalizing hitch, aka...torsion bars.</font>
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THUD! Of course, great point. Load equalizers provide a responsive torque on the frame, counteracting the torque of the tongue weight around the rear axle. They effectively lengthen the wheelbase of the truck to include the trailer. My buddy used to call them "ladder bars for trailers"...
 
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