Is tongue weight static weight or dynamic weight?

[fuzzybabybunny]

My Subaru Crosstrek XV has a tongue weight limit of 200lb. The trailer hitches I can install on the Crosstrek have a tongue weight limit of 350lb.

I want to install a trailer box onto the hitch:

https://www.google.com.hk/search?q=...tJaaTmwXkqIGICA&ved=0CBwQsAQ&biw=1920&bih=947

Based on this tongue weight limit, does it mean that the box + contents hanging on the tongue cannot exceed 200lb?

What if the car is going over bumps and the thing bounces around? The dynamic weight could exceed 200lb then. Even a 100lb box + contents could exceed 200lb if it was bouncing...

 

[Raizinman]

It means that the box + contents hanging on the tongue cannot exceed 200lb.

Don't overanalyze it. It is very simple.

I've seen people with a bathroom scale getting a tongue weight.

 

[fuzzybabybunny]

Yeah, like you said, a single person standing on the trailer hitch could exceed the tongue weight. Does that mean that simply having a person standing on the back could result in the hitch snapping off? Or the front wheels to not have enough weight on them for control?

I feel like a solid piece of steel bolted in numerous spots to the frame of the car should be able to withstand FAR more hanging off of it than just 200lb...

 

[NutBucket]

It's not that the hitch will fall off. The concern is overloading the rear suspension of the vehicle. Think of a Porsche 911; lots of weight behind the rear axle can cause some "interesting" handling characteristics.

 

[Hail The Brain Slug]

Yeah, like you said, a single person standing on the trailer hitch could exceed the tongue weight. Does that mean that simply having a person standing on the back could result in the hitch snapping off? Or the front wheels to not have enough weight on them for control?

I feel like a solid piece of steel bolted in numerous spots to the frame of the car should be able to withstand FAR more hanging off of it than just 200lb...

It probably CAN withstand far more than 200 pounds, but that's not why it's rated in the first place. The rating has to do with your specific vehicle, its suspension, handling characteristics, and how it is affected when towing a trailer. Overloading the tongue weight could lead to unsafe and unpredictable handling. Remember, the weight on the hitch is outside the vehicle, so it has a lot of leverage on the frame.

 

[xBiffx]

Like has been stated. This is about suspension and not absolute weight limits for the frame/hitch.

It's rather difficult to steer a vehicle that doesn't have its front wheel firmly planted on the ground.

 

[Humpy]

Yeah, like you said, a single person standing on the trailer hitch could exceed the tongue weight. Does that mean that simply having a person standing on the back could result in the hitch snapping off? Or the front wheels to not have enough weight on them for control?

I feel like a solid piece of steel bolted in numerous spots to the frame of the car should be able to withstand FAR more hanging off of it than just 200lb...

Most vehicles where a Class I hitch receiver would be installed don't have a frame to bolt to. The hitch on my Mazda 3 is bolted to the fairly thin gauge sheet metal of the uni-body. I am somewhat concerned about damage due to bikes bouncing around and try to be careful over big bumps. My Forester has mounting points built in to the uni-body that are more robust but the tongue weight limit is still 200 lbs.

The European version of the Mazda has a tow rating but the US version doesn't allow towing at all. With the smaller hitches for cars the specifications don't seem to have as much to do with physics as they do some other reasoning.

 

[Meghan54]

Remember, any weight that you put on the hitch counts against your vehicle's weight carrying capacity, whatever it is (listed on a sticker in one of the door jambs.)

 

[WackyDan]

It means that the box + contents hanging on the tongue cannot exceed 200lb.

Don't overanalyze it. It is very simple.

I've seen people with a bathroom scale getting a tongue weight.

What he said... There is also some margin of error, so if you are at 225, I wouldn't get too worried.

 

[Zenmervolt]

Or the front wheels to not have enough weight on them for control?

It's this. Along with the amount of weight that the rear suspension can take.

Realistically speaking, you can probably get away with slightly (and I mean slightly) more tongue weight with a box like that than with a trailer, because part of the consideration with a trailer is the effect of the trailer's tendency to sway and pull the car from side to side in heavy winds, as well as the fact that a trailer's weight push down on the tongue more during braking.

Basically, the tongue weight value is a static weight value that is designed to be light enough to accommodate the dynamic effects of a trailer with that amount of tongue weight.

Remember though that any tongue weight will count against your Rear Axle Weight Rating (and, by extension, the overall GVWR). It is very likely that you will max out the rear axle rating before you max out the overall GVWR.

ZV

 

[Gillbot]

It's this. Along with the amount of weight that the rear suspension can take.

Realistically speaking, you can probably get away with slightly (and I mean slightly) more tongue weight with a box like that than with a trailer, because part of the consideration with a trailer is the effect of the trailer's tendency to sway and pull the car from side to side in heavy winds, as well as the fact that a trailer's weight push down on the tongue more during braking.

Basically, the tongue weight value is a static weight value that is designed to be light enough to accommodate the dynamic effects of a trailer with that amount of tongue weight.

Remember though that any tongue weight will count against your Rear Axle Weight Rating (and, by extension, the overall GVWR). It is very likely that you will max out the rear axle rating before you max out the overall GVWR.

ZV

I would respectfully disagree with your thought that you can get away with sightless more weight on a box as opposed to a trailer, if for only the simple fact of the leverage force. With a trailer, the wheels of the trailer help support the wight of the load whereas with the box, it's all on the receiver. With my truck, I can't tell as much when I'm pulling a trailer as opposed to my motorcycle rack.


With the rack back there, it makes the truck feel more bouncy.

 

[heymrdj]

Yup super light tongue weights thanks to the frame of the vehicle not really being there. You're talking multiplication of forces, and by the time you have 200lbs bouncing off the receiver, you've got many times that force on the mount points. That's why the number is so low. If they didn't build in any wiggle room they'd give you some insane number like 800lbs. You can trailer more, as the wheels of the trailer support 80% of the load, while the receiver is just left to straight line pull.

Sometimes, depending on the model of car the receiver is made for, it comes with the requirement that a support strap is used to even reach the 200lbs. This allows bounce forces to be transferred to another part of the vehicle, like the liftgate, instead of the receiver mount. These are only required when racks, bike racks ect are used with the hitch instead of a trailer, again because of unsupported tongue weight loads.

http://www.etrailer.com/Accessories-and-Parts/Curt/18050.html

 

[Raduque]

https://www.google.com.hk/search?q=...tJaaTmwXkqIGICA&ved=0CBwQsAQ&biw=1920&bih=947

Ya know, there's a reason why all the pics show this thing attached to a truck, SUV or van...

 

[thomsbrain]

Most vehicles where a Class I hitch receiver would be installed don't have a frame to bolt to. The hitch on my Mazda 3 is bolted to the fairly thin gauge sheet metal of the uni-body. I am somewhat concerned about damage due to bikes bouncing around and try to be careful over big bumps. My Forester has mounting points built in to the uni-body that are more robust but the tongue weight limit is still 200 lbs.

The European version of the Mazda has a tow rating but the US version doesn't allow towing at all. With the smaller hitches for cars the specifications don't seem to have as much to do with physics as they do some other reasoning.

Correct. The model-specific name-brand hitches on most passenger cars carry the vertical weight on the sheet metal on the bottom of the trunk (often using the tow loop), not a "frame." The horizontal forces are generally carried by the rear sub-frame, so that's fairly tough, but the tongue rating is limited by the strength of the trunk.

That said, there are places that build custom hitches and you could probably have one built that didn't utilize sheet metal attachments.

 

[Triumph]

I would respectfully disagree with your thought that you can get away with sightless more weight on a box as opposed to a trailer, if for only the simple fact of the leverage force. With a trailer, the wheels of the trailer help support the wight of the load whereas with the box, it's all on the receiver. With my truck, I can't tell as much when I'm pulling a trailer as opposed to my motorcycle rack.


With the rack back there, it makes the truck feel more bouncy.

I would never put something like this on a car (I don't mean a motorcycle, I mean those generic platforms that people put their beer coolers and dead deer on), for exactly the reason you mentioned - the leverage it puts on the receiver is NOT the same as putting an equivalent trailer tongue weight on the ball. Unibody cars just aren't meant for abuse like this. A ladder frame truck is a different story.

 

[Zorba]

A trailer is simply supported, meaning the tongue ball and tires get a vertical force only, i.e. no torque is applied at the ball. Racks are cantilevered so in addition to the vertical load, they create a torque on the hitch, basically what everyone means by leverage. the idea of the strap is to make the rack simply supported like a trailer (at last to some extent).

I would suspect that trailer suspension would also help with the bounce.

But the rating in the book is a static number, and if it needed to be lower for a rack, the book would say. Also be sure to check the manual of the rack, some require a strap to be used.

 

[Meghan54]

A trailer is simply supported, meaning the tongue ball and tires get a vertical force only, i.e. no torque is applied at the ball. Racks are cantilevered so in addition to the vertical load, they create a torque on the hitch, basically what everyone means by leverage. the idea of the strap is to make the rack simply supported like a trailer (at last to some extent).

200# is 200#, whether it's applied by a rack hanging off the back or from the tongue weight of a trailer attached....both apply torque to the hitch.

I don't know where you get trailers don't apply torque from.

 

[BoberFett]

200# is 200#, whether it's applied by a rack hanging off the back or from the tongue weight of a trailer attached....both apply torque to the hitch.

I don't know where you get trailers don't apply torque from.

200# is not 200#. Hell, 10# isn't 10#. Hold 10# in one hand close to your body, then extend your arm and hold it out from your body.

A trailer has all it's weight directly on the hitch ball. A rack will extend it out past the hitch ball.

 

[Triumph]

200# is 200#, whether it's applied by a rack hanging off the back or from the tongue weight of a trailer attached....both apply torque to the hitch.

I don't know where you get trailers don't apply torque from.

No. No it is not. The location of the 200 pounds is not over the ball, typically, with a hitch mounted rack.

 

[xBiffx]

200# is not 200#. Hell, 10# isn't 10#. Hold 10# in one hand close to your body, then extend your arm and hold it out from your body.

A trailer has all it's weight directly on the hitch ball. A rack will extend it out past the hitch ball.

This.

In physics terms, its referred to as a moment. A moment is just a measure of force and distance. As the distant from the hitch increases while the weight (force) stays the same, so does the moment. The force component of a moment is torque.

This is where Achimedes came up with his "Give me a lever long enough and a fulcrum on which to place it, and I shall move the world" line. The further you are away, the less force it takes. In this case, the less force it takes to break something.

/nerd

 

[BoberFett]

Not to mention, if you load a trailer correctly, it can have zero hitch weight. Throw 2000 pounds of bricks on the front of your trailer, and your Civic is done for. Put them over the trailer axle evenly, and while your drivetrain and brakes might not enjoy it, you don't have to worry about ripping the hitch right off the vehicle.

 

[Greenman]

Not to mention, if you load a trailer correctly, it can have zero hitch weight. Throw 2000 pounds of bricks on the front of your trailer, and your Civic is done for. Put them over the trailer axle evenly, and while your drivetrain and brakes might not enjoy it, you don't have to worry about ripping the hitch right off the vehicle.

Pulling a trailer with zero hitch weight will be extremely unstable. Rule of thumb is 10% of the trailer weight on the hitch.

 

[BoberFett]

That makes sense, thanks for the correction.

 

[Ferzerp]

Yup, you don't want the load ever having the ability to pull up on the rear of the vehicle. They don't handle very well when the rear end gets light, especially while pulling a trailer.

 

[Brian Stirling]

Pulling a trailer with zero hitch weight will be extremely unstable. Rule of thumb is 10% of the trailer weight on the hitch.

You are correct sir...


Brian