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Tongue Weight Rating and Wheelchair Hitch Mounted Carrier Vehicle Modifications

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


What is Tongue Weight Rating and How Does it Relate to the Ability to Safely Carry a Wheelchair Hitch Mounted Carrier?

Tongue weight or load is the amount of load that presses down on the vehicle's hitch.  If the car is carrying too much tongue weight then it can experience steering, handling, and braking problems.  Where the tongue weight is being carried by the vehicle is past the rear axle.  A compounding effect is created in that as tongue weight is carried by the towing vehicle's hitch, weight is actually transferred from the front tires (axle) to the rear tires (axle), much like a seesaw.  The vehicle's rear axle ends up carrying more load than just the dead weight of the hitch load.  Obviously the tongue weight 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.

 

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Manufacturer's Ratings Related to a a Wheelchair Hitch Mounted Carrier

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

You also have to consider the types of vehicles that customers will attempt to install a wheelchair hitch mounted carrier onto.  In most cases the 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 inside the vehicle, it would be used. 

The vehicle is typically smaller and older and often not intended to have the semi-permanent load of a wheelchair hitch mounted carrier.  At most the manufacturer had in mind a temporary trailer used by the family on a summer vacation.  While your vehicle is carrying the additional load, you will need to service your vehicle more frequently, following your manufacturer's severe duty preventive maintenance schedule. 

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

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

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

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

How do I find the vehicle's Rated Tongue Weight? 

This is only found in your 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 Vehicle Can Handle

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

Tongue Weight

Tongue weight (TW) is the downward force exerted on the hitch by the combined weight of the wheelchair hitch mounted carrier and the wheelchair or scooter.  We know from a seesaw that both the amount of force and distance from the pivot point, in our case the rear axle, are important.  There appears to be no industry defined distance for where the typical hitch point is located from the rear axle.  The wheelchair hitch mounted carrier platform and the wheelchair or scooter load are both located considerably farther from the rear axle than the typical hitch ball would be.  The combined wheelchair hitch mounted carrier platform and the wheelchair or scooter load will therefore have a larger effect on the vehicle and this will be taken into account in our calculations.    

Vehicle 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 car's gross vehicle weight rating (GVWR) minus the car's curb weight.  Therefore, you may not need to obtain your car'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 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 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 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.

Note: be very careful about using internet values on curb weight.  If there is any doubt, be safe and put the car on a scale. 

Vehicle Rear Axle Curb Weight

While you were getting your vehicle weighed on a scale to get a curb weight, 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 vehicle. 

Wheelchair or Scooter Weight

You need to know the weight of your wheelchair or scooter including batteries.  You can either get this from the manufacturer or weigh it on a scale.


How do I Calculate How Heavy a Wheelchair Hitch Mounted Carrier My Towing Vehicle Can Carry?

You will need to ensure that the wheelchair hitch mounted carrier does not cause your 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.  Hitch mounted carriers are bolted to the car's hitch receiver and are considered vehicle modifications.  As such, NHTSA has rules governing how gross vehicle weight rating GVWR and gross vehicle axle weight rating GAWR calculations are performed. 

First calculation, maximum tongue weight

Add the weight of the hitch mounted carrier and the wheelchair or scooter.  If this load was being applied at a hitch ball mount, this would be your tongue weight.  However, adding the weight of the hitch and mobility device actually adds more load to the rear axle than just the combined weight.  With a wheelchair hitch mounted carrier, the downward load is applied further away from the rear axle than at a hitch ball mount.  The load is approximated to be all at the center of the hitch mounted carrier platform.  The downward force applied further away from the rear axle will transfer load from the front axle and apply it to the rear axle.  You can imagine that if the downward force was great enough or the distance from the rear axle sufficiently large, the car would pivot about the rear axle and the front tires would come off the ground.  This transfer of weight is happening even if it's (hopefully) not large enough to lift the front wheels off the ground or you can't see it.  The combined weight of the hitch mounted carrier and wheelchair or scooter will have to be adjusted to account for this extra effective load on the rear axle. In order to calculate the amount of weight the wheelchair hitch mounted carrier is adding to the rear axle, use the following formula:

Weight added to rear axle = (W x (A + W.B.)) / W.B.

Where:

W=combined weight of the wheelchair hitch mounted carrier and wheelchair or scooter

A=distance from the rear axle to the centerline of the hitch mounted carrier platform

W.B. = vehicle wheelbase

Compare the weight added to the rear axle by the combined weight of the wheelchair hitch mounted carrier and wheelchair or scooter to your vehicle's tongue weight rating.  If the car's tongue weight rating is exceeded, then you can't install the hitch mounted carrier.   

Second calculation, Load Carrying Capacity or GVWR

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 car's gross vehicle weight rating (GVWR) minus the car's curb weight.  Ensure the vehicle has load carrying capacity to support 150 lbs per designated seating positions, sufficient cargo load, and the weight of the vehicle modifications (hitch, wheelchair or scooter, wheelchair hitch mounted carrier, and any other modifications).  If there is not sufficient load carrying capacity, then you have to reduce the number of designated seats if possible or you can't install the hitch mounted carrier.  

If you car doesn't have 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'll need to first obtain the curb weight of your vehicle.  You will add to this number, 150 lbs per designated seating positions, the weight of a reasonable cargo load, and the weight of the vehicle modifications (hitch, wheelchair or scooter, wheelchair hitch mounted carrier, and any other modifications).  Adding the weight of all cargo and passenger load plus the hitch mounted carrier load to the curb weight will give you your vehicle's Gross Vehicle Weight (GVW).  Compare GVW to GVWR.  GVW must never exceed GVWR.  If GVW does exceed GVWR then you have to reduce the number of designated seats if possible or you can't install the hitch mounted carrier.  

Third calculation, rear axle GAWR

Once you've obtained the rear axle curb weight of your vehicle, it gets tricky to calculate how the weight of all cargo and occupants that the 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.  As a first assumption, consider all weight that is carried between the 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 hitch mounted carrier load.  As discussed above, the hitch mounted carrier load will actually add more load to the rear axle than just the combined weight of the hitch mounted carrier and mobility aid.  The formula above should be used in determining the rear axle load.  Compare your vehicle's rear axle load 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.   


Hitch Selection and Tongue Weight Rating

The hitch is the frame that is attached to your vehicle and provides a female square interface for receiving the wheelchair hitch mounted carrier, perhaps with a coupler.  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 weight they can handle.  It is extremely important to realize that your vehicle's ultimate tongue weight rating is determined by the weakest component in your system, whether that is your vehicle's ratings, the hitch ratings, or the coupler rating.   Simply installing a class IV hitch on a vehicle DOES NOT mean the vehicle is rating to carry 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 hitch mounted carrier calculations.

The overall hitch rating for tongue weight is determined by the lowest ratings of the hitch, drawbar, or hitch ball coupling.  Whichever component has the lowest tongue weight rating sets the maximum rating of the overall hitch system.  Remember, the hitch's maximum tongue weight rating is NOT necessarily your vehicle's rating.  In all cases, the hitch must not be modified in an attempt to increase it's 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.


Frequently Asked Questions About Tongue Weight Rating and Wheelchair Hitch Mounted Carriers

The hitch on my car is a Class 3 hitch, can I safely install a hitch mounted carrier that installs 100lbs and use it to carry my 250lb  wheelchair?  No.  The combined weight of the hitch mounted carrier and wheelchair is 350lbs.  Even assuming that the tongue weight rating of the vehicle is 350lbs, there is not sufficient tongue weight rating to support the combined hitch mounted carrier weight.  This is because the 350lbs that the hitch platform will carry adds more load to the rear axle than just the 350lbs.    

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