How does GCVWR affect stopping if you have trailer brakes?

Hypothetically, in a perfect world, the trailer stops itself.
But if you’ve towed much, you’d know that isn’t always the case, for various reasons.
Additionally, it’s more than just braking ability that go into the combined weight rating.

SAE J2807 tow ratings allow for trailer brakes to be required, for tow ratings over 3,000 pounds. The owner's manual will state the threshold when brakes are required in order to be compliant with this standard. Some vehicles can achieve max tow rating without trailer brakes (Ford Explorer is one example), but modern pickups with their huge numbers absolutely require them.

2020 F150 Owner's Manual wrote:
"Important: The towing vehicle’s braking system is rated for operation at Gross Vehicle Weight Rating, not at Gross Combined Weight Rating. Separate functional brakes should be used for safe control of towed vehicles and for trailers where the Gross Combined Weight of the towing vehicle plus the trailer exceed the Gross Vehicle Weight Rating of the towing vehicle."

FWIW - the actual standard for trailer stopping performance is:
The combination is required to stop completely from 20 mph in 80 feet or less. During this stop test, the trailer must remain within an 11.5-foot-wide lane throughout the entire stop. In addition to the active testing, the parking brake must be able to hold the truck and trailer firmly in place both upward and downward on a 12 percent grade when it is at the maximum GCWR.

crasster wrote:
I've read many times that exceeding GCVWR is a stopping safety issue.

What I'm not understanding is the GCVWR assuming there are NOT electric brakes?

Is it assuming trailer brake failure and the vehicle's GCVWR can fully stop both trailer and TV?

From my experience, a well tuned brake controller the brakes just feel like stopping without a load at all.


So how does exceeding GCVWR cause a safety issue stopping with electric brakes?

Just curious, not doing it.

Actually. Your tow vehicles brakes are only designed to stop the GVWR of the vehicle. NOT the GCVWR. that is why trailer brakes are required. So your TV can safely stop it's own max weight (GVWR). Anything over that the trailer brakes are supposed to stop.
Yes the TV brakes may stop the trailer. Eventually. But not safely, especially in a E stop.

Terryallan wrote:

crasster wrote:
I've read many times that exceeding GCVWR is a stopping safety issue.

What I'm not understanding is the GCVWR assuming there are NOT electric brakes?

Is it assuming trailer brake failure and the vehicle's GCVWR can fully stop both trailer and TV?

From my experience, a well tuned brake controller the brakes just feel like stopping without a load at all.


So how does exceeding GCVWR cause a safety issue stopping with electric brakes?

Just curious, not doing it.

Actually. Your tow vehicles brakes are only designed to stop the GVWR of the vehicle. NOT the GCVWR. that is why trailer brakes are required. So your TV can safely stop it's own max weight (GVWR). Anything over that the trailer brakes are supposed to stop.
Yes the TV brakes may stop the trailer. Eventually. But not safely, especially in a E stop.

Okay thank you! I learned something new today. :)

Brakes on any vehicle are sized to the axle their on.

A 7000 lb trailer axle = 7000 lb of braking performance.

Same with the tow vehicle.
A one to DRW with 9900 rawr and 6000 fawr = 15900 lbs of braking performance at a minimum.

A triaxle trailer/7k axles = 21000 lb of braking performance.
Now add the trucks 15900 lbs of braking performance = 36900 lbs of braking performance.

As someone mentioned the trucks brakes stops the truck and the trailer brakes stops the trailer. If they don't then there is a reason why...but its time to get them fixed.

Do a search as to how the SAE certification process is done.

I thought it was GCWR

The brakes on the vehicle help stop the trailer and this is designed into the vehicle. That's why trucks have such huge brakes for their size. Notice the brakes on trucks have gotten bigger over the years? Not because the trucks themselves are that much heavier, it's because they can tow much more than they used to.
The more weight you add to a given setup, the longer the stopping distance.

I have upgraded brakes on my truck and it stops the whole 17K# load faster.

BTW, I have seen both Ford and GM write about this very subject and they make it clear that the trucks are part of the formula and have a major impact on stopping the trailer. So yes, it is clearly part of the certification or more accurately, it's part of the design criteria.

My opinion and experience is they each stop them selves if each are in good shape.

Terryallan wrote:

crasster wrote:
I've read many times that exceeding GCVWR is a stopping safety issue.

What I'm not understanding is the GCVWR assuming there are NOT electric brakes?

Is it assuming trailer brake failure and the vehicle's GCVWR can fully stop both trailer and TV?

From my experience, a well tuned brake controller the brakes just feel like stopping without a load at all.


So how does exceeding GCVWR cause a safety issue stopping with electric brakes?

Just curious, not doing it.

Actually. Your tow vehicles brakes are only designed to stop the GVWR of the vehicle. NOT the GCVWR. that is why trailer brakes are required. So your TV can safely stop it's own max weight (GVWR). Anything over that the trailer brakes are supposed to stop.
Yes the TV brakes may stop the trailer. Eventually. But not safely, especially in a E stop.

This is the correct answer!!