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Towing Capacity and Wheelchair Trailer Vehicle Modifications

Note: Always consult your vehicle and trailer owner's manuals and follow their guidance.  This is intended as a general overview but because each towing situation is different, your vehicle and trailer manufacturers will be the best sources of information on towing with their equipment.

What is Towing Capacity?

Towing capacity is simply a measure of how heavy a trailer a vehicle can tow, i.e. a towing vehicle's capacity for towing, not to simply rearrange words.  There are several reasons for a vehicle manufacturer to limit the towing vehicle's towing capacity.  The main reasons to set a towing capacity are:

 

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What is Tongue Load Rating and How Does it Relate to Towing Capacity?

Tongue load is the amount of the trailer's weight that presses down on the towing vehicle's hitch.  Approximately 10-15% of the trailer's total weight should be carried by the towing vehicle as tongue weight.  Having too little or too much tongue weight being carried by the towing vehicle can cause towing problems.  If the towing vehicle is carrying too little tongue weight then the trailer will tend to sway.  If the towing vehicle is carrying too much tongue weight then the towing vehicle can experience steering, handling, and braking problems.  The reason that too much tongue load is an especially dangerous problem is that the hitch point where the tongue load is being carried by the towing vehicle is past the rear axle.  A seesaw effect is created in that as tongue load is carried by the towing vehicle's hitch, weight actually is transferred from the front tires to the rear tires.  The towing vehicle becomes back heavier than just the dead weight of the tongue load.  Obviously this should never get to the point that you see the front tires come off the ground but it's happening nonetheless.  Less weight being carried by the front tires means the front brakes are less effective, handling is effected, and steering is effected.   

Manufacturer's Ratings Related to Towing Capacity

It is not a simple task to figure out how heavy a trailer your vehicle can safely tow.  There are numerous calculations that have to be applied if you are to be absolutely certain that you are within all of your vehicle's manufacturer's stated weight limits for towing a wheelchair trailer.  The limits that will be affected by towing and have to be checked are:

On the one hand, a wheelchair trailer really shouldn't be that big of a load.  You have an approximately 300lb trailer and the weight of the power wheelchair, let's say typically 225lbs.  525lbs of Gross Trailer Weight (GTW), not very big in the world of trailer towing.  But you have to consider the types of vehicles that customers will use to tow their wheelcahri trailer.  In most cases the towing vehicle can't support any other modifications that would allow for the transportation of the power wheelchair.  If there was another way to transport the power wheelchair, it would be used.  While towing a power wheelchair is better than no solution, towing in general has several disadvantages. 

The towing vehicle is typically smaller and older and often not intended for full duty towing.  At most the manufacturer had in mind a temporary trailer used by the family on a summer vacation.  While you are towing a trailer, you will need to service your towing vehicle more frequently, following your manufacturer's severe duty preventive maintenance schedule.  Most wheelchair trailers stay installed and become what can be considered permanent vehicle modifications. 

How do I find the towing vehicle's maximum payload?

This is found on the towing vehicle's Tire Label found either on the towing vehicle's B pillar or edge of the driver's door.  If any vehicle modifications have been installed on the towing vehicle, the weight of the adaptive equipment must be subtracted from the payload listed on the Tire Label.  The vehicle modifier can either place a new Tire Label over the original or attach a separate label next to the Tire Label that indicates by how much the payload has been reduced.

How do I find the towing vehicle's GVWR Gross vehicle weight rating?

This is found on the towing vehicle's Safety Compliance Certification Label found either on the towing vehicle's B pillar or edge of the driver's door.

How do I find the towing vehicle's GAWR Gross axle weight rating? 

This is found on the towing vehicle's Safety Compliance Certification Label found either on the towing vehicle's B pillar or edge of the driver's door.

How do I find the towing vehicle's GCWR Gross Combined Weight Rating?

This is only found in your towing vehicle's owner's manual.  The GCWR Gross Combined Weight Rating will be listed in a table, if at all.  Some manufacturers instead simply list the towing vehicle's Maximum Loaded Trailer Weight Rating instead.  Some list both the GCWR Gross Combined Weight Rating and Maximum Loaded Trailer Weight Rating.

How do I find the towing vehicle's Maximum Loaded Trailer Weight Rating?

This is only found in your towing vehicle's owner's manual.  Sometimes it's listed in a table and sometimes it's not listed because a GCWR Gross Combined Weight Rating is listed instead.  Some list both the GCWR Gross Combined Weight Rating and Maximum Loaded Trailer Weight Rating.  Sometimes your vehicle's owner's manual will say that you vehicle is not intended to tow and that's the end of that.  When a Maximum Loaded Trailer Weight Rating is listed it's frequently done in a table and the exact value depends on your vehicle specifics like engine size, transmission type, if your vehicle has a towing package, and even the rear axle ratio.  Sometimes the Maximum Loaded Trailer Weight Rating will have multiple values depending on the towing vehicle cargo and passenger load.  Sometimes its given as a range from 0 - XXXX lbs.  If that's the case, the highest value is your Maximum Loaded Trailer Weight Rating. If it is just a listed number with no towing vehicle cargo loading caveats, it's very important that the vehicle user understand the assumptions that make up the the towing vehicle's Maximum Loaded Trailer Weight Rating.  It assumes a towing vehicle with only mandatory options, no cargo being carried either internally or externally, a trailer tongue load of 10–15%, no passengers in the vehicle besides the driver, and a driver who weighs 150lbs.  If any of your actual loading conditions differ from the assumptions, the towing vehicle's Maximum Loaded Trailer Weight Rating is reduced accordingly.  In other words, if you are the driver and you weigh 200lbs instead of the assumed 150lbs, your towing vehicle's Maximum Loaded Trailer Weight Rating is reduced by 50lbs.

If your towing vehicle's owner's manual lists both the weight-carrying and weight distributing Maximum Loaded Trailer Weight Ratings, ALWAYS USE the weight carrying rating.  The weight distribution capacity will always be greater than the weight carrying capacity and you might be tempted to use it, however, NEVER use the weight distribution rating in performing wheelchair trailer calculations.

How do I find the towing vehicle's Rated Tongue Load? 

This is only found in your towing vehicle's owner's manual.  Sometimes it's listed in a table, sometimes it's listed in a paragraph in the section of the owner's manual dealing with trailer towing, and sometimes it's not mentioned at all.  In those cases where it is not mentioned at all, use 10% of the Maximum Loaded Trailer Weight Rating. 

Weights Needed to Determine How Heavy a Wheelchair Trailer My Towing Vehicle Can Tow

Before you can start calculating you're going to need to measure (whenever possible) or estimate the weights of different loads. 

Wheelchair trailer

Gross trailer weight (GTW) is the weight of the trailer fully loaded in its actual towing condition.  GTW is measured by placing the fully loaded wheelchair trailer on a vehicle scale.   The entire weight of the trailer should be supported on the scale, no wheels off the side.  For an estimate, the wheelchair manufacturer can tell you how much the wheelchair trailer weighs empty.  To this you would add the weight of your power wheelchair which you can obtain from the owner's manual, contacting the manufacturer, contacting the company that services your power wheelchair etc. 

Tongue Weight

Tongue weight (TW) is the downward force exerted on the hitch ball by the trailer coupler, i.e. the direct force that the towing vehicle is carrying on its suspension due to the wheelchair trailer.  This should be between 10 to 15% of GTW.

Tongue weight of up to about 300 lbs. can be measured on a household scale by resting the trailer coupler on the scale and placing the scale on a box so that the coupler is raised to its normal towing height. The trailer must be fully loaded and level. 

Curb Weight

If you car has a FMVSS No. 110, Tire selection and rims Tire Label found either on the towing vehicle's B pillar or edge of the driver's door, you will use the manufacturer's stated load carrying capacity.  Load carrying capacity is simply the towing vehicle's gross vehicle weight rating (GVWR) minus the car's curb weight.  Therefore, you may not need to obtain your towing vehicle's curb weight.  Curb weight is the empty (empty of any passenger or cargo load) weight of a vehicle full of fuel and topped off with all fluids.   Curb weight does not include any passenger (no driver too) or cargo load.  Generally, you will need to weigh your vehicle in order to determine it's curb weight.   If your vehicle manufacturer can tell you the curb weight of your vehicle that is fine.  It will not be listed in your towing vehicle's owner's manual.  You really don't have to weigh the vehicle absolutely empty to determine curb weight  and if you read how to do the calculations you'll understand why.  If you know, for instance, who will be riding in your towing vehicle and they are available, you can have them sit in the car when it's being weighed on the scale.  Same goes for any cargo load that you will normally be carrying.  Of course, if you're measuring the towing vehicle's curb weight with additional load, you wouldn't then be adding that same load in the calculations below to find GVW and GCW.

Rear Axle Curb Weight

You first need to know the rear axle Curb Weight of your towing vehicle.   So while you were getting your vehicle weighed on a scale, simply drive off of the scale a little bit until only the back wheels are left on the weight scale.  The scale's measurement is the rear axle curb weight of the towing vehicle.

How do I Calculate How Heavy a Wheelchair Trailer My Towing Vehicle Can Tow?

You will need to ensure that the wheelchair trailer does not cause your towing vehicle to exceed any weight rating.  So each one has to be looked at.  You should first perform some calculations to give you a good approximation which should then be followed with actual weight measurements.

First calculation, maximum payload

Add the weight of all cargo and passenger load including trailer tongue load.  Include the weight of the hitch if the installer did not already reduce the towing vehicle's maximum payload.

Compare actual payload to maximum payload. 

Second calculation, GVWR and GVW

Once you've obtained the curb weight of your towing vehicle, you will add to this number the weight of all cargo and occupants that the vehicle will be carrying internally and externally.  Don't forget to add in the tongue weight (TW). 

Adding the weight of all cargo and passenger load (including trailer tongue load) to the curb weight will give you your towing vehicle's Gross Vehicle Weight (GVW).

Compare GVW to GVWR.  GVW must never exceed GVWR.  If GVW does exceed GVWR then you have to lessen either your cargo load or passenger load sufficiently.  

You may think, why do I need to concern myself with GVWR when I'm towing and other than the wheelchair trailer, my vehicle won't be heavily loaded?  Well, maybe you don't but you should always be concerned with GCWR which is covered below and for which you need your GVW.  Your towing vehicle’s braking system is rated for operation at GVWR, not at GCWR.  When NHTSA requires the vehicle manufacturer to test the brakes and make sure they stop your car, that's done at its GVWR.  So how will your towing vehicle's brakes handle when loaded to the higher GCWR, who knows?  Separate functional trailer brakes need to be used for safe control of towed vehicles and for trailers where the GCW of the towing vehicle plus the wheelchair trailer exceed the GVWR of the towing vehicle.  You just need to see what your exact loading condition is and proceed accordingly. 

Third calculation, rear axle GAWR and rear axle GVW

Once you've obtained the rear axle curb weight of your towing vehicle, it gets tricky to calculate how the weight of all cargo and occupants that the towing vehicle will be carrying internally and externally will affect the rear axle specifically.  I'd recommend running through the calculations and if you are close, look at ways to reduce your load.  You could of course load your towing vehicle (without the trailer attached) with whatever cargo and passenger load it will normally carry, take it back to the scale and re-weigh the rear axle curb weight.  As a first assumption, consider all weight that is carried between the towing vehicle's tires to be evenly distributed between the front and rear axles.  Any weight that is carried behind the rear axle is going to be carried exclusively by the rear axle, including the 10-15% of the wheelchair trailer's Gross trailer weight (GTW) that is being carried as tongue load.  These are just assumptions, the physics is a little more involved.  Actually obtaining a loaded rear axle weight will makes things a little easier.

Compare your loaded towing vehicle's rear axle weight to the GAWR for the rear axle.  The weight carried by the rear axle must never exceed its GAWR.  If the weight carried by the rear axle does exceed its GAWR then you have to lessen either your cargo load or passenger load sufficiently.

Again, you may think, why do I need to concern myself with GAWR when I'm towing?  If you are driving around by yourself in an empty vehicle with just your wheelchair trailer attached, you probably don't need to concern yourself with GAWR.  But your vehicle's loading condition very likely will change and GAWR and GVWR are critical safety ratings.  They are mandated by NHTSA and must never be exceeded.  Whenever you are adding load to a car, you should at least be thinking about GAWR and GVWR.    

Fourth calculation, GCWR, GCW, and GVWR

If your vehicle's owner's manual lists a GCWR, to obtain the Gross Combined Weight GCW, add your towing vehicle's Gross Vehicle Weight GVW calculated above plus the Gross Trailer Weight GTW.  Compare your towing vehicle's GCW to the manufacturer's Gross Combined Weight GCWR.  GCW must never exceed GCWR.  If it does, you'll either have to figure weighs to reduce your towing vehicle's or trailer's load, not tow, or use a different towing vehicle.  

Now compare GCW to GVWR.  If GCW exceeds GVWR, you will need to have separate functional trailer brakes.  Your towing vehicle’s braking system is rated for operation only up to GVWR.  

Fifth calculation, Maximum Loaded Trailer Weight Rating

To determine if the towing vehicle can tow the wheelchair trailer:

Towing vehicle’s Maximum Loaded Trailer Weight Rating -  (Cargo load) - (Passenger load) +/- (difference in weight between driver and 150lbs, if the driver is heavier than 150lbs the additional weight is subtracted) - (Weight of any vehicle modifications that would effect your vehicle's factory curb weight, for example  the weight of the hitch, hand controls, etc.).

Positive Result

If the number you get from the above calculation is POSITIVE, you are NOT exceeding your towing vehicle's Maximum Loaded Trailer Weight Rating.  If the number is small, you should look for ways to reduce your towing vehicle's load. 

Negative Result

If the number you get from the above calculation is NEGATIVE, you ARE exceeding your towing vehicle's Maximum Loaded Trailer Weight Rating and it is NOT safe to tow the wheelchair trailer.  Either you'll have to reduce cargo load, passenger load, go on a diet, etc. or find a better towing vehicle with a higher Maximum Loaded Trailer Weight Rating. 

Note: When the Gross Trailer Weight GTW is more than 1,500 lbs, separate functional trailer brakes will be required.  Some towing vehicle owner's manuals state 2,000lbs is the cutoff and you should always use the manufacturer's recommendations.  You also will need to be familiar with any state laws requiring separate functional trailer brakes, including states that you might just be passing through. 

Hitch Selection, Drawbar, Hitch Ball and Towing Capacity

The hitch is the frame that is attached to your towing vehicle and provides a female square interface for receiving a coupler/drawbar of some sort.  The size of the square interface is a towing industry standard and is determined in part by the hitch class.  Hitches come in standard ratings based on the gross trailer weight GTW and tongue load they can handle.  It is extremely important to realize that your towing vehicle's ultimate maximum trailer weight rating and tongue load rating are determined by the weakest component in your system, whether that is your towing vehicle's ratings, the hitch ratings, or the coupler rating.   Simply installing a class IV hitch on a vehicle DOES NOT mean the towing vehicle is rating to tow Class IV loads!

The hitch rating is found on a sticker on the hitch, usually near the receiver.  Sometimes the information is stamped into the hitch frame.

A label affixed to the hitch receiver provides both the weight-carrying and weight distributing capacities for the hitch receiver.  The weight distribution capacity will always be greater than the weight carrying capacity, however, always use the lower weight carrying rating.  NEVER use the weight distribution rating in performing wheelchair trailer calculations.

The overall hitch ratings for maximum towing capacity and tongue load are determined by the lowest ratings of the hitch, drawbar, or hitch ball coupling.  Whichever component has the lowest towing and tongue load rating sets the maximum rating of the overall hitch system.  Remember, the hitch's maximum trailer and tongue load ratings are NOT your towing vehicle's maximum ratings. 

Hitch Classifications

Class I trailer hitch

Trailer hitch with capacity of up to 2,000 lbs gross trailer weight and 200 lbs tongue weight.

Class II trailer hitch

Trailer hitch with capacity of up to 3,500 lbs gross trailer weight and 300/350 lbs tongue weight.

Class III trailer hitch

Trailer hitch with capacity of up to 5,000 lbs gross trailer weight and 500 lbs tongue weight.  2" receiver

Class IV trailer hitch

Trailer hitch with capacity of up to 10,000 lbs gross trailer weight and 1,000 - 1,200 lbs tongue weight.

The wheelchair trailer should normally ride parallel to the ground or road when being towed.  At installation of the trailer, the height between the hitch receiver (firmly attached to your vehicle and isn't moving) and the trailer will need to be matched .  This is accomplished with the drawbar or coupler which is the piece of metal that is insert and secured into the female hitch receiver.  Usually for towing applications, it will include a hitch ball coupling.    By selecting the right drawbar, the installer can make the two interfaces match properly.  If you are having a hitch installed in anticipation of towing, you should not attempt to also buy a coupler or drawbar at that time.

Drawbar Rating

The drawbar has a label that will state the maximum towing load rating and tongue load it can handle.  The label is typically mounted on the shaft that goes into the hitch receiver.  It can also be stamped into the draw bar, on the mounting plate where the coupling or ball receiver is mounted.  

Hitch Ball Rating

The drawbar has a label that will state the maximum towing load rating and tongue load it can handle.  The label is typically mounted on the shaft that goes into the hitch receiver.  It can also be stamped into the draw bar, on the mounting plate where the coupling or ball receiver is mounted.

Frequently Asked Questions About Towing Capacity and Wheelchair Trailers

The hitch on my car is a Class 3 hitch, can I safely tow up to 3,500lbs?  You don't know.  The amount that any vehicle can safely tow is limited by the individual ratings of all the items used to tow (vehicle, hitch, drawbar, hitch coupling) as well as various manufacturer determine weight ratings or limits (see above).  The hitch rating is but one rating that will determine the overall safe towing capacity of your vehicle.  When the hitch is not installed by the manufacturer, it is not uncommon for the hitch to be rated to a higher towing and tongue load capacity than the towing vehicle on which it is mounted, so you should definitely not assume what your vehicle is capable of  by simply using the hitch's rating .  

What if my vehicle has a maximum loaded trailer weight rating of 1,500lbs, do I still install a Class I hitch even though its rated to 2,000lbs?  Yes, you'll just have to keep in mind that the maximum that you can tow will be limited by the vehicle's towing rating and the other vehicle weight ratings not the higher hitch rating.

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