How does GCVWR affect stopping if you have trailer brakes?

[crasster]

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.

[blt2ski]

JIMNLIN wrote:

drsteve wrote:
Trucks have big brakes so that you can go to the landscape supply yard, load 3000 lb of gravel in the bed, and still be able to stop in a reasonable distance.

It's not always about towing.

Good point.
And evident of truck camper owners carrying a 4k-6k TC on a '20 3500 DRW GM with 6k fawr and 10500 rawr. Thats 16500 lb of braking performance at a minimum.
The truck may weigh in the 9000 lb range so the owner has over 7k lb of braking performance to play with.
Dangz ...GM sure raised the bars with those big 10500 lb rawr numbers on the new '20 trucks.

Both comments are why I recommend trailer brakes when trailer is heavier than payload amount. Even if law allows s heavier trailer. I stopped quicker with my two 35 series Dullys when I put brakes on a single axle 3500 capacity trailer, than no brakes. Just because requirements say X, you can or may want to go below.

Marty

[JIMNLIN]

drsteve wrote:
Trucks have big brakes so that you can go to the landscape supply yard, load 3000 lb of gravel in the bed, and still be able to stop in a reasonable distance.

It's not always about towing.

Good point.
And evident of truck camper owners carrying a 4k-6k TC on a '20 3500 DRW GM with 6k fawr and 10500 rawr. Thats 16500 lb of braking performance at a minimum.
The truck may weigh in the 9000 lb range so the owner has over 7k lb of braking performance to play with.
Dangz ...GM sure raised the bars with those big 10500 lb rawr numbers on the new '20 trucks.

[Slownsy]

And that is why all trailers over 4500kg has to have approved air brakes in Australia so when things go wrong those brakes pulls you op.
Frank.

[drsteve]

Trucks have big brakes so that you can go to the landscape supply yard, load 3000 lb of gravel in the bed, and still be able to stop in a reasonable distance.

It's not always about towing.

[Grit_dog]

So big trucks have bigger brakes becasue they have so much power you can drive faster....than what? A bicycle?
My big truck with big brakes was not only a turd for power without a tuner, it's also geared to redline in 6th by 100mph and anything over about 85 is uncomfortably high rpms for cruising.
Must be why it has big brakes. Orrrrrr because it's designed to haul and tow big stuff.
Now our car has even bigger and better brakes because it IS designed to go real fast and yes it'll stop quicker than 99% of the cars on the road, yet it's not designed to tow anything.
So maybe, just maybe, the slow truck has big brakes to stop more than just itself.
But what's safe? No matter how good of brakes I put on the truck and trailer it won't stop nearly as quick as the car,nor most cars, even one with "average" brakes.

[Terryallan]

Mickeyfan0805 wrote:

Terryallan wrote:

Mickeyfan0805 wrote:

Terryallan wrote:

Mickeyfan0805 wrote:

Cummins12V98 wrote:
My opinion and experience is they each stop them selves if each are in good shape.

And the other -in an emergency. Brake lines blew on the TV when trying to avoid an idiot who cut me off on the interstate last summer. It was the trailer brakes that got us to safety!

Could you not use your parking / E brake on the truck? Those are operated mechanically. Have a cable that pulls them on.

In the moment of slamming on the brakes, there would not have been time. It was the fact that I had a hydraulic controller on the Suburban that kept activating the trailer brakes even after losing the TV brakes trailer kept slowing enough to avoid a wreck. From there, e-brakes could have worked, but didn't need to. The trailer brakes worked flawlessly to draw us to safety.

So it probably wouldn't have worked with a normal proportional brake controler. they only apply the brakes as much as they feel the TV braking. Good to know.

Just wondering. Did you gear it down to help the brakes to stop it? Easy to think of all this stuff while it isn't happening I know. Just thinking what I would do if it ever happened to me. A learning experience if you will.

I am not entirely sure regarding the proportional controller. I think you are right that it wouldn't have worked in this manner. That said, some might have a manual override that would allow you to accomplish the same thing by engaging the controller manually. I haven't had a proportional controller in 8 years, and only had that for 18 months, so I don't remember for sure.

As for gearing, it wasn't necessary. The lines really weren't bad enough that they should have blown (the guy at the shop was shocked). I really had to jam the brakes to avoid the other car, and the truck slowed significantly before the lines blew - at which time we were already moving pretty slowly. From there it was simply a slow crawl to safety.

Glad it worked out for you. You are correct that proportional controlers do have a manual over ride. Not sure I could reach it or think to pull it in time. but it is there

[Terryallan]

opnspaces wrote:

SweetLou wrote:

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!!

I disagree with the above statements. As embarrassing as it is to say I have been guilty of once forgetting to plug the umbilical in when coming home from a camping trip. I made a 1.5 hour highway speed drive with 4 complete stops and several slowing for mountain highway curves and never even realized the trailer was unplugged. It was only before I hit the last steep downhill that I remembered and pulled over to plug the trailer in. And the brakes had been working so well up to this point that I debated not stopping at all and just going home.

Yes my trailer brakes do work and I can definitely feel it when they engage. My point is that the brakes on a properly sized tow vehicle will stop the trailer as well.

I bet never once in all that driving did you have to use the brakes in a HARD, or emergency stop. Meaning did you ever brake hard enough to get into the antilock?

So unplug the trailer brakes, and head toward a brick wall at 60 mph, and hit the brakes 200 feet from the wall. See if the truck brakes alone stop you in time. That is what we are talking about. will they stop you. yes EVENTUALLY. But can they safely stop you in a emergency full on brake pedal to the floor stop? NO. and they are NOT designed to do it.

I have had to do a hard stop, and I heard the Trailer tires crying just above lock up. If they had not been doing their part. I would have had a pretty bad accident. As it was. I stopped 10 feet before I would have hit.

I had long discussions with a man / engineer, that designs brakes for vehicles, Chrysler, Ram. and he finally got thru to me that brakes on ANY vehicle are only designed to stop the GVWR of that vehicle.

Now if you don't have the truck loaded to the max GVWR. say you got 1000lb left over. then the Tv will stop 1000lb of the trailer. But you gonna need more than that.

[Mickeyfan0805]

Terryallan wrote:

Mickeyfan0805 wrote:

Terryallan wrote:

Mickeyfan0805 wrote:

Cummins12V98 wrote:
My opinion and experience is they each stop them selves if each are in good shape.

And the other -in an emergency. Brake lines blew on the TV when trying to avoid an idiot who cut me off on the interstate last summer. It was the trailer brakes that got us to safety!

Could you not use your parking / E brake on the truck? Those are operated mechanically. Have a cable that pulls them on.

In the moment of slamming on the brakes, there would not have been time. It was the fact that I had a hydraulic controller on the Suburban that kept activating the trailer brakes even after losing the TV brakes trailer kept slowing enough to avoid a wreck. From there, e-brakes could have worked, but didn't need to. The trailer brakes worked flawlessly to draw us to safety.

So it probably wouldn't have worked with a normal proportional brake controler. they only apply the brakes as much as they feel the TV braking. Good to know.

Just wondering. Did you gear it down to help the brakes to stop it? Easy to think of all this stuff while it isn't happening I know. Just thinking what I would do if it ever happened to me. A learning experience if you will.

I am not entirely sure regarding the proportional controller. I think you are right that it wouldn't have worked in this manner. That said, some might have a manual override that would allow you to accomplish the same thing by engaging the controller manually. I haven't had a proportional controller in 8 years, and only had that for 18 months, so I don't remember for sure.

As for gearing, it wasn't necessary. The lines really weren't bad enough that they should have blown (the guy at the shop was shocked). I really had to jam the brakes to avoid the other car, and the truck slowed significantly before the lines blew - at which time we were already moving pretty slowly. From there it was simply a slow crawl to safety.

[opnspaces]

SweetLou wrote:

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!!

I disagree with the above statements. As embarrassing as it is to say I have been guilty of once forgetting to plug the umbilical in when coming home from a camping trip. I made a 1.5 hour highway speed drive with 4 complete stops and several slowing for mountain highway curves and never even realized the trailer was unplugged. It was only before I hit the last steep downhill that I remembered and pulled over to plug the trailer in. And the brakes had been working so well up to this point that I debated not stopping at all and just going home.

Yes my trailer brakes do work and I can definitely feel it when they engage. My point is that the brakes on a properly sized tow vehicle will stop the trailer as well.

[Terryallan]

Mickeyfan0805 wrote:

Terryallan wrote:

Mickeyfan0805 wrote:

Cummins12V98 wrote:
My opinion and experience is they each stop them selves if each are in good shape.

And the other -in an emergency. Brake lines blew on the TV when trying to avoid an idiot who cut me off on the interstate last summer. It was the trailer brakes that got us to safety!

Could you not use your parking / E brake on the truck? Those are operated mechanically. Have a cable that pulls them on.

In the moment of slamming on the brakes, there would not have been time. It was the fact that I had a hydraulic controller on the Suburban that kept activating the trailer brakes even after losing the TV brakes trailer kept slowing enough to avoid a wreck. From there, e-brakes could have worked, but didn't need to. The trailer brakes worked flawlessly to draw us to safety.

So it probably wouldn't have worked with a normal proportional brake controler. they only apply the brakes as much as they feel the TV braking. Good to know.

Just wondering. Did you gear it down to help the brakes to stop it? Easy to think of all this stuff while it isn't happening I know. Just thinking what I would do if it ever happened to me. A learning experience if you will.

[Grit_dog]

Terryallan wrote:

Mickeyfan0805 wrote:

Cummins12V98 wrote:
My opinion and experience is they each stop them selves if each are in good shape.

And the other -in an emergency. Brake lines blew on the TV when trying to avoid an idiot who cut me off on the interstate last summer. It was the trailer brakes that got us to safety!

Could you not use your parking / E brake on the truck? Those are operated mechanically. Have a cable that pulls them on.

Oh, ya sure, you betcha. 1 tiny little drum or disc (especially on a truck old and rusty enough to blow a brake line) will not do squat compared to 2 or 4 presumably serviceable trailer brakes.

[Mickeyfan0805]

Terryallan wrote:

Mickeyfan0805 wrote:

Cummins12V98 wrote:
My opinion and experience is they each stop them selves if each are in good shape.

And the other -in an emergency. Brake lines blew on the TV when trying to avoid an idiot who cut me off on the interstate last summer. It was the trailer brakes that got us to safety!

Could you not use your parking / E brake on the truck? Those are operated mechanically. Have a cable that pulls them on.

In the moment of slamming on the brakes, there would not have been time. It was the fact that I had a hydraulic controller on the Suburban that kept activating the trailer brakes even after losing the TV brakes trailer kept slowing enough to avoid a wreck. From there, e-brakes could have worked, but didn't need to. The trailer brakes worked flawlessly to draw us to safety.

[Groover]

ScottG wrote:
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.

The big reason that trucks have large brakes for their size is that empty tow vehicles generally have a high power to weight ratio, enabling people to drive faster with or without a trailer. The faster you drive the more brakes you need. You may notice that most performance cars have big brakes even though they have zero rated tow capacity. The big brakes do help stop trailers as an added benefit but the problem with that is then your braking ability is limited to the traction that the truck has. As your trailer get heavier that becomes a bigger and bigger issue. To stop quickly you need every tire on the ground doing all it can to help. If your trailer axles are carrying twice as much weight as the truck axles are and the trailer brakes fail you are going to take at least 3 times farther to stop, no matter how good the truck brakes are. In this case, fade resistant truck brakes will help keep the distance from being more than 3 times as far.

In general, a 7K axle on a trailer does not need to be as large as the brakes on a 7k truck axle because you physically can't do repetitive stops as frequently due to the mass of the trailer slowing your acceleration. The brakes have longer to cool down during the slower acceleration and when you do use them the power produced by engine is split between more brakes.

Good trailer brakes also help prevent jacknife situations.

[valhalla360]

I haven't read the SAE but I guarantee they have some fudge factors in their.

It's all well and good to say the trailer stops itself but reality is especially away from commercial operators, that's often not the case.

Plus, just having one operational brake on the trailer and none on the truck...you will likely eventually come to a stop on level ground...but I wouldn't want to try it in real life.