Overview

The intent of the post is design considerations for a tow vehicle when compared to the ultimate tow vehicle a class 8 semi.  Although I may reference one of the big three the intent is not to bias any manufacturer.  Sorry this is long but that is how I roll.

Engine           

The engine is probably the first thing considered when looking at a tow vehicle.  This is probably the biggest marketing tool for the big three and the biggest gains in the last few years and way overkill.  The big three need to stop the HP & Torque war.

Semi Trucks typically have 350 to 550 horsepower and 1000 to 1800 ft-lbs of torque from a diesel power plant.  We will probably see close to 500 horsepower and 1000 ft-lbs of torque coming from Ford or Ram or both in the next year or two. 

Recommend:  Diesel >300 horse power & > 700 ft-lbs torque with exhaust/turbo brake

Drivetrain

Semi’s have two dually air suspension axle’s with a very robust transmission to support the tongue weight of the trailer.

In general as the power increases the drivetrain is improved to handle the power.  Most lightduty drivetrains are comparable with the exception of the F450 that does borrows the rear axle from the medium duty trucks.  Ram started offering air assist rear suspensions and I would highly recommend this option.

Bill and Linda wrote:

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RAM in the 3500HD does offer, as an option, the commercial transmission that is used in the true class 4 and 5 trucks.  You might want to add that under “Drive Train.” 

 

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Recommend: Dually rear axle with air suspension Rear GAWR > 9k lbs & Front GAWR > 5k lbs

Frame

Semi’s have a C-channel frame that allows the hitch to be mounted between the frames.

All but Ford use a boxed frame. A box frame tends to be stiffer and in general stiffer is better.  Ford will claim some flex is good to provide a better ride but 2017 they are significantly improving the stiffness.

Recommend: Box frame is probably better for light duty trucks

Part 1

Andy

Trailer Weight

First of all you should never tow over the manufacturing weight limits and the biggest Achilles heal is the Rear GAWR of all manufactures 5^th wheel towing! 

This is where my opinions have been ill received but I consider light duty truck limits (class 3) to be ~20k lbs. and above this the truck is just not heavy enough to control the weight especially if there is a problem with the trailer brakes.  This is about safety and longevity of the tow vehicle.

Empty TV to Gross Trailer Ratio 

A class 8 semi empty weight is ~ 20k lbs and typical loaded trailers are ~50k lbs for a total of ~70k lbs.  This is a 2.5 times ratio 50/20 = 2.5.  Yes I know class 8 semi’s have an 80k rating but most big rigs are not loaded to the max. 

Applying this ratio to a class 3 light duty truck.  Typical truck empty weight ~8.5k lbs. and 2.5 times this gives us a trailer weight of ~21.5k lbs. 

Loaded TV to Trailer Axle Weight Ratio

Another way to look at this is GVW rating.  A class 8 truck has a GVW >33k lbs so if a loaded semi is 35k lbs and the trailer axle weight is 35k lbs for a total of 70k lbs (same scenario above) this gives us a loaded weight TV to trailer axle weight ratio of 1:1.

Applying this to a class 3 truck.  GVW of a class 3 truck is 14k lbs so that would mean we can add 14k lbs of trailer for a total of 28k lbs of GCVW.  Trailer weight here would be GTVW 14k lbs – Empty weight 8.5k lbs = 5.5k lbs + Trailer axle weight of 14k lbs = ~19.5k lbs gross trailer weight which is close to the 21.5k lbs number above or the general rule of 20k lbs.

Part 2

Andy

Summary

The engine, frame, & drivetrain of the big 3 all have in my opinion maxed out the Class 3 truck ratings.  There is not much more they can do to increase the GCVW or 5th wheel towing without going to a Class 4 or larger truck. 

When towing, a heavier not lighter tow vehicle, is better for stability of the combined towing package.  Tail wagging the dog.  If you have to select a 4x2 or regular cab to get the tow vehicle as light as possible to tow your trailer, your trailer is to heavy & you should consider going to a MDT or HDT truck or lighter trailer. 

Caution and careful consideration is needed when towing a trailer larger than 20k lbs with a class 3 truck.  Balance is just as important as gross weights.  Most trucks will max out the rear GAWR of the tow vehicle before any other rating is surpassed.  As a rule of thumb keep your GVW of your trailer no more than 2.5 times your empty tow vehicle weight or loaded tow vehicle weight close to the same weight as your trailer axle weights.

Final

Andy

Andy:

Good report from someone who hasn’t paid any attention to the marketing dribble.

Couple of points –

RAM in the 3500HD does offer, as an option, the commercial transmission that is used in the true class 4 and 5 trucks.  You might want to add that under “Drive Train.”

I do disagree on the just “greater than” 9K rear axle and 5K front axle.  – Here’s why:

All the 2011 and forward trucks have very high bed rails.  The trailer to truck bedrail issue is a bigger one than most realize; that is until they run the bed rails of the truck into the trailer and then the dollars just roll out the door.

So to go to a hauler bed to address this issue one needs more rear axle capacity when the trailer pin weight gets into the high 3,000’s or even low 4,000’s and that is quite possible with a trailer even lighter than 20K. (“Ask me how I know this.”)

Simply stated 5K won’t handle the front axle loads.  Look more for 5,600#+. That 600# does make a difference.  (BTW, if the hitch is properly installed almost no weight from the 5er goes on the front axle but most other carried items do impact the front axle.)

That said the weight allowance for the bed and possibly an aux fuel tank should be taken into consideration if one is “designing” a tow vehicle.  Air ride hitches also will add over well over 350# to the rear axle.  All these items add up on the rear axle loads.

I do want to mention thatit’s good to see someone else has done the math, figured out and done a post stating it’s the rear axle weight rating - actually the remaining  rear axle capacity after the truck's base weight -  that almost always runs out before other ratings.  That is a big help for those making selections – especially with the new – rather heavy trailers regardless of brand.

Bill,

Great points and I added your comment to the original post on the Ram transmission.

Axle ratings and my points of greater than 9k & 5k are to point out that hauling such a heavy load is going to require DRW.  Also if you go with a 4x2 you will have a lot less front axle empty weight and rating.  Your points are spot on and I think confirm these ratings.

This is probably going to cause additional controversy but I do not consider it feasible to add a hauler bed to a Class 3 truck & tow a reasonably sized full time 5th wheel trailer.  It was my intention to add the hauler bed to our tow vehicle and I even went as far as meeting with the Utility Bodywerks guys (great guys & beautiful hauler bed) but the additional weight of the hauler bed plus filling all of those bins full is to much rear axle weight & GVW.

I have the Airsafe 25k hitch and VW before installation was 9,270 lbs (full fuel & me) and after is 9,580 lbs (full fuel, me, & airsafe hitch) so I figure the hitch and adapter are ~310 lbs.  Note this only leaves 4,420 lbs for king pin weight and anything else that I want to bring with before hitting the 14k total.  Rear axle in the hitch configuration was 4,360 lbs adding 4,420 lbs is 8,780 lbs well under the 9100 lbs rear axle rating.  In my case I run out of GVW before GAWR....balance is just as important as gross weight.

Extra fuel tank considerations.  I think this should be considered only after getting your tow vehicle and trailer.  Load everything up and head to the scale.  The tank itself is going to weigh ~30 - 50 lbs and diesel weighs ~7lbs per gallon so an additional 30 gallon tank is going to run ~250 lbs.  The nice thing is you don't have to fill if needed....airplanes do this all the time to compensate for range vs. load.  Also the location of the tank is probably going to be centrally located and will probably add weight to the front and rear axles. 

Andy

It seems hard to pin down exactly how much additional weight a hauler bed adds. Sure it depends on design and accessories added but even ball park numbers over the stock PU bed are seemingly hard to come by. I have seen numbers as high as 950 extra pounds vs the stock PU bed. That could slash available pin weigh to the low 3000s on some models. 

Bill's point on the hauler bed, being an important consideration is bed rail clearance in certain situations not related to towing capability. If you factor in the hauler bed as a must have then you'll simply be limited more in what you can tow. We are looking at trailers in the 18.5 to 19K range and hauler bed equipped TV. Based on good counsel by Bill and others we feel the GM and RAM 3500s currently fit the needs we envision more than adequately. The Ford's lower axle rating is cause for concern for us. This could change with future iterations of the Ford product and with 3 years to go before we hit the road we will keep an open mind, including the possibility of some more "exotic" TV options like an HDT. 

Folks my trucks GVW 14K is just a number! The reality is they limit it to that for licensing and insurance reasons. Same goes for the F450.

My RAM has a 6K front axle with 5,460 sitting on it and the rear is rated at 9,750# with 9,580 sitting on it so do the math I am over by 1,000#. It's just a number!

Brian - Yes Bill and others here have a lot of good information and his point on bed rails is great information and overlooked.  Jack Mayer mentioned this to me and was a factor in choosing the Airsafe Hitch.  This hitch has a significant amount of adjustment for the bed to trailer clearance. 

I will keep you posted on my weights as we purchased a trailer in that same range: empty weight ~15k & gross weights 18.5k - 19k lbs.

As an FYI as I posted in the previous response the GAWR rating isn't a factor for my setup.

Andy

As to hitch adjustment, anecdotal evidence suggests that raising the fiver hitch to clear the bedrails has the negative side effect of unleveling the trailer when travelling which can cause it's own issues but can be compensated for by raising the trailer (which, by the by, also causes clearance problems).  Don't know much about the AirSafe Hitch as we aren't that far into that area of research but we will add it to the list of things to look into.

Brian - Hopefully the clearance and trailer level will be close enough if not then it might be a trip to Morryde for adjustments or another look at the hauler bed.

Cummins12V98

I do agree with you to a point that numbers are numbers and to some extent is what I pointed out in the F350 vs. F450 discussion.  I could say the same for the rear axle rating of the F450 being that it comes from the MDT.  The F350 with same springs & drive train rate the rear axle to 9,650 lbs so why not say a number is just a number so lets set the F450 axle rating to 9,650 lbs or 12,000 lbs from the MDT, or why not 14,000 lbs from Dana. 

My F450 is insured as a commercial vehicle with a 16k GVW rating even though I told them it was a class 3 truck so numbers being numbers maybe this is what I should change my GVW to.

Having said that (and poking a little fun.....don't take it personally) I am not going to tell anyone that they should run their vehicles over ratings even though a majority do knowingly or not.  Is it going to hurt anything....maybe maybe not.  I also think a person with your experience of towing heavy has a lot better handle of his rig and is a big part of the equation to towing safely. But I personally see way to many huge 5th wheels running down the road towed with F250/2500 SRW dragging the bumper.....how far down the path do we go saying a number is a number.   

Personally I am going to stay within the manufactures ratings and I am going to do that for a few reasons.....

1.) I am a novice to hauling heavy (as you rightly have called out and I do not deny) :)

2.) I want my truck and trailer to last a long time 10 - 20 years

3.) I want to tow with confidence in the mountains

4.) I don't want to chance a fine

Types of Towing Numbers

DOT = Axle ratings and GVW ratings for class of truck

If a trucker goes through the scales with an axle or GCVW rating over the limit they can go to jail so I don't think the argument of numbers are numbers would work in their defense.  Also if you are in an accident with your rig and the police can confirm you were over ratings you might be fined whether it was your fault or not but unlikely.

Manufacturer's = Derived from Engineering numbers to the make the marketing people happy

I would say Fords F450 GCVW rating of 40,400 number is a marketing number that is nearly impossible to achieve unless everything is perfect.

Engineering = Typically in the design of mechanical components an engineer will build in a safety factor sometime 3 to 1 but almost always over rated (airplanes are one exception).

The safety factor builds in safety for poor materials, poor workmanship, abuse, age, etc., so that it will perform over the life of the product to the manufacturer's numbers or design intent.  It is easy to site one time examples like the Tundra towing the space shuttle or VW towing a Boeing jet but there is no way this can be done safely or daily understanding that these are extreme cases.

Andy

BiggarView wrote:

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It seems hard to pin down exactly how much additional weight a hauler bed adds. Sure it depends on design and accessories added but even ball park numbers over the stock PU bed are seemingly hard to come by. I have seen numbers as high as 950 extra pounds vs the stock PU bed. That could slash available pin weigh to the low 3000s on some models. 

Bill's point on the hauler bed, being an important consideration is bed rail clearance in certain situations not related to towing capability. If you factor in the hauler bed as a must have then you'll simply be limited more in what you can tow. We are looking at trailers in the 18.5 to 19K range and hauler bed equipped TV. Based on good counsel by Bill and others we feel the GM and RAM 3500s currently fit the needs we envision more than adequately. The Ford's lower axle rating is cause for concern for us. This could change with future iterations of the Ford product and with 3 years to go before we hit the road we will keep an open mind, including the possibility of some more "exotic" TV options like an HDT. 

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A comment or two on the height of the hitch – be careful you don’t end up with a trailer that is nose high which equals more weight on the rear axles of the trailer. 

The trailer needs to be level and the truck needs to be level.  When that is done correctly you can’t compensate for high bed rails by raising the hitch or the pin box, etc.  If you could you wouldn’t need a hauler bed to solve the bed rail issues.

I believe all in this discussion are well aware of that fact but I make the comment for those "reading along" for information.

On Edit, yes a trip to MOR/ryde can many times solve bed rail clearance issues along with the elimination of springs, etc. It depends on the trailer's height before lift. 

As to a class 3 truck with a hauler bed and aux fuel tank being acceptable for a 20K or less trailer within all ratings:  Yes, actually the Chevy 3500HD can do that as can the RAM 3500HD.  The “balance” is fine.  The F-450 can as well depending on the size of the aux tank and will likewise do an excellent job.  I base all this on actual weights taken by Howard and Linda twice when they were doing the wheel-by-wheel weighing and that’s with an aluminum Classy Chassis hauler bed, light bar, 60 gallon aux tank, my tools and a fixed hitch. I was running an air-ride pin box which is a much lighter net weight than say a Trailer Saver. 

I just say all this to say, once again, “It depends” on the specific installation.  But I have zero issues putting a hauler bed on a class 3 truck if one knows all the other weights ahead of time and factors them in and then doesn’t go purchase a 22K trailer.  The math vs. specifications work just fine and the scales confirm them .  But one must factor in all the “stuff.”

BTW, I also agree about future interactions of the F-450.  Ford may finally allow the rating the rumored new truck frame for the pickup it most likely deserves.  But that will be a 2017 at least.

Comment to Andy - Now that you brought up trading fuel for weight capacity in an airplane I now have another perspective on your comments.  Pilots are trained to live in the "green," be very careful in the "yellow," and just stay out of the "red."  That training tends to really carry over to other things.

All good stuff.

Edited to add MOR/ryde comment.