5/24/20 1:52 p.m.

Hi all,

I've done some googling and searching and have found very little on this subject.

I recently purchased a large (32') enclosed bumper tow trailer. It's big (two car), but heavy (plywood and steel). The tare weight vs gross weight is... bad. 4600lbs tare vs 10,000lbs gross. I would like to try to lighten this trailer to increase the payload.

Disclaimer: I did my research. It fits my mission/budget almost perfectly as it sits. However, I am interested in being able to fit either more equipment or heavier vehicles​​​​ in the trailer.

Now, I probably don't want to go drilling speed holes in the frame, and lightweight foam/glassboard/aluminum flooring is prohibitively expensive. Then I noticed that the entire inside of the trailer is finished in 1/4" plywood. I figure that I can save approximately 300lbs of tare weight by removing the plywood and replacing it with plastic sheeting (for weathertight-ness). Any I crazy or is this a good idea?

Purple Frog (Forum Supporter)
Purple Frog (Forum Supporter) Reader
5/24/20 2:08 p.m.

All that work to arrive at 4,400 tare vs. 10,000 gross?  The juice isn't worth the squeeze.


tux424 New Reader
5/24/20 2:46 p.m.

I for one am surprised they would build/sell a 32ft trailer with tadum 5k axles. Figure by the time a single car and any tools are in there you'd be nearing the max weight.

You figure most trailers are built as cheaply as possible, not sure how much "meat" is left on the bone to be removed.

Patrick (Forum Supporter)
Patrick (Forum Supporter) GRM+ Memberand MegaDork
5/24/20 3:23 p.m.

Add 7k axles and springs?

L5wolvesf Reader
5/24/20 3:52 p.m.

Aluminum Marston (beach) matting for the floors

81cpcamaro Dork
5/24/20 5:53 p.m.

The plywood helps make the walls a bit more rigid, so removing may not be as helpful as you hope.

Sounds like the 10lk gross weight is to get it under some states rules, trailer probably can handle more weight, just been derated a bit. Bet it has 7K axles, my 28ft had 5200 lb axles with gross of 9990 lbs. Check the tag on the axles to see what they are rated for.

nimblemotorsports HalfDork
5/24/20 6:07 p.m.

Thin fiberglass roof to save weight, foam sandwich, heck sides too with foam/glass like boat.  I suspect the majority of weight in the frame/deck at that length it must be very stiff

djsilver (Forum Supporter)
djsilver (Forum Supporter) Reader
5/24/20 6:39 p.m.

You didn't say what brand of trailer you bought, but I checked the Featherlight website for comparison, as they advertise light weight as a feature.  Their 32' bumper pull enclosed car trailer (#4926) has (2) 7000# axles and tare weight is 4,700lbs,  I couldn't find any gross weight ratings on their website, but your trailer is 100lb lighter, so not out of line.  You may lighten it up with composite inside panels, or even alumalite (or similar) flooring to replace the plywood, but that would be quite expensive.  

This links shows an 8.5 x 32' enclosed trailer at 4,600lbs, but shows 2 different payload capacities depending on 5,200lb (9,800 gross) or 7,000lb (11,600 gross) axles.  If yours has the 5200lb axles you could probably legally increase the payload capacity by switching to 7,000lb axles.  

USA Cargo Trailer Weights

frenchyd GRM+ Memberand PowerDork
5/24/20 8:59 p.m.

In reply to Rally_AJ :

I was in the exact same problem. Haul 2 cars and tools/equipment/spares. 
The way I achieved that was use expired prepeg carbon fiber ( you can usually find that for around the price of fiberglass cloth),  2 layers. A layer of 1/8th thick foam and a layer of Kevlar. Then the frame of the trailer I Used thin wall steel frame.  The deck was surplus aluminum honeycomb sandwich 1&1/8 inch thick with luan bonded. 
 I shortened overall length by putting the first car in backwards and winching the second  over the hood of the first.  That got everything down to  28 feet instead of 32 Saving those 4 feet  was a massive weight savings. Plus it worked out to to fit in with my 4 foot modules. 
The temptation was to go for an aluminum frame. 3M had a bonding material tested  with Kevlar but by the time I did the structural calculation aluminum was 143 pounds heavier.  Plus I didn't have a good source for Aluminum but a surplus metal place had exactly the steel I in needed in stock at 40% of market price. So I took a chance and used it on steel.  Decades later when the owner loaded a  heavy tractor in the back end ( yes tail heavy)  he lost control on a sharp turn. By the time it rolled down the hill and the tractor had managed to punch it's way out  the trailer was well and truly  totaled but the "fiberglass" was still fully bonded. 

djsilver (Forum Supporter)
djsilver (Forum Supporter) Reader
5/25/20 12:46 p.m.

Here is a summary of DOT rules.  The manufacturer may have de-rated it to allow use without a CDL.  

"There are three key aspects to consider when assessing CDL operator requirements for commercial work trucks involved in towing a trailer: truck GVWR, trailer GVWR and GCWR of the truck-trailer combination. Trailer GVWR is most critical to determining when a CDL is required. When a trailer has a GVWR of 10,001 pounds or more and the combined GCWR of the truck and trailer is 26,001 pounds or more, a CDL is required by the operator. For example, if a trailer has a GVWR of 11,500 pounds and is towed by a truck with a GVWR of 15,000 pounds, resulting in a GCWR of 26,500 pounds, then the operator must have a CDL.

In contrast, when the trailer in the truck-trailer combination has a GVWR of 10,000 pounds or less, the CDL requirements allow for a greater GCWR for both the truck and trailer without requiring a CDL license. For example, a truck with a GVWR of 26,000 pounds or less can tow a trailer with a GVWR of 10,000 pounds or less and not require the operator to have a CDL under federal requirements. However, CDL requirements mandate that the truck and trailer GVW not exceed 26,000 pounds and 10,000 pounds, respectively. In short, the truck and trailer cannot be overloaded."

frenchyd GRM+ Memberand UltimaDork
7/28/21 10:50 a.m.

In reply to thomaspeket :

Much of the cost of fuel is the cost of pushing air.  The weight savings really would only effect acceleration.  

jimbbski SuperDork
7/28/21 3:04 p.m.

The only way to effectively have a lighter MT weight is to start out with a trailer with an aluminum frame vrs a steel one.  Anything you do won't make much of a difference.  A few years ago i was looking for a 20 footer as a 24 ft was just to long and while some offered 22 ft options it would have to be custom built and I didn't want to wait for that to happen.  I compared the difference between the common steel frame trailer and the aluminum ones and went with an aluminum trailer by ATC. I never weighed the trailer MT but I'm sure it's under 2500# and still has a 7K gross load cap. 


frenchyd GRM+ Memberand UltimaDork
7/28/21 3:30 p.m.

In reply to jimbbski :

You might be disappointed but just using aluminum is no promise of lighter weight. The first Jaguar D type race cars had aluminum front subframes. When  they switched to steel the factory saved something like 23 pounds per car. 
     An Aluminum trailer is even harder to retain strength  over steel.  Since there is no depth relative to length.  In addition steel tends to have greater ductility over Aluminum. That's why connecting rods are made of steel rather than Aluminum except in drag racing where they are frequently replaced.   

jimbbski SuperDork
7/29/21 4:17 p.m.

ATC is a quality trailer builder and I did my homework before I bought my aluminum trailer.  There are semi-trailers built with aluminum, both box and flatbed. I think that if there was a problem with building with aluminum by now it wouldn't still be used.  

frenchyd GRM+ Memberand UltimaDork
7/29/21 4:39 p.m.

In reply to jimbbski :

You may be right. My comment was about weight and not quality.  Aluminum is lighter than steel. But it's not as strong as steel so more of it is needed. And the weight goes up. 
  You can reduce the amount needed with a greater cross section but car trailers by design tend to be loaded so the main bending moment is over the axles.   Hence the difficulty of reducing the weight of aluminum over steel.  
        I go back to Jaguar D type. Steel turned into a lighter subframe than Aluminum. 
I personally hate that. Aluminum is harder to weld, doesn't mix well with typical trailer suspension parts. And needs periodic painting if the dreaded tin worm is to be avoided. 

Now a lighter weight aluminum trailer could be designed.  With the use of a Monique type construction.  That however would put the cargo (the race car) uncomfortably higher with attending loading issues. 

codrus (Forum Supporter)
codrus (Forum Supporter) GRM+ Memberand PowerDork
7/29/21 5:36 p.m.
frenchyd said:

I personally hate that. Aluminum is harder to weld,

AIUI, it's the welding that's at the root of the problem here.  Welded aluminum has been annealed and is low strength, to get the strength back it needs to be heat-treated, but nobody has an oven big enough to heat treat an entire trailer frame.  (Well, Lockheed probably does, but they aren't building trailers...)  So you need more material and your weight savings mostly evaporate.

Trailex builds trailers using bolted aluminum extrusions, which makes them significantly lighter.  They've got an open car trailer that's a little over 700 pounds and a 24 foot enclosed that's 2700.  They're not cheap though.


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