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Old 11-03-2020, 08:04 AM   #1
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When braking how much trailer weight transfers to TV ?

I am happy with the braking performance of our combination (GMC Canyon and 20' FC). Looking at the 2021 Canyon/Colorado, it appears GM has gone from a 4 piston front caliper to a 2 piston floating caliper common to Acadia and Cadillac AT* passenger cars. Not sure of performance difference but I prefer the 4 piston fixed just by design.

Got me thinking about trailer braking and TV brakes. Wondering that under heavy braking and trailer brakes right at point of locking, what percentage of trailer weight (or mass/force) is transferred forward to the TV? Obviously some significant amount is, or the braking distance would be the same as the TV without a trailer. Not talking about light braking where braking is ideally shared close to equally.

Looking at braking standards, SAE has "recommended practice" standards J134/J135.

Apparently only states that actually have performance requirements set a pretty low bar (I believe WV should be "ft/sec^2" not "ft/sec" in which case about 0.4G).

West Virginia: A motor vehicle or combination of motor-drawn vehicles must be capable of stopping at the following rates as if on a dry, smooth, level free road: (1) vehicles or combinations of vehicles with brakes on all wheels must be able to decelerate at a speed of 14 feet per second; and (2) vehicles or combinations of vehicles not having brakes on all wheels must be able to decelerate at a speed 10.7 feet per second.

Wyoming: Every combination of vehicles must have a service braking system that will stop the combination of vehicles within 40 feet from an initial speed of 20 mph on a level, dry, smooth, hard surface.
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Old 11-03-2020, 09:48 AM   #2
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GM Eboost concept

So this would be great....

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Old 11-03-2020, 10:07 AM   #3
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I sure don't have an answer about weight transfer and that video demonstrated a concept but no details about what it is that decreased stopping distance as demo'd.

But if you are serious about putting the brakes on your AS Dexter 4 piston brakes are a bolt on IF your axles are Nev-R-Lube.

I did a test fitment on another trailer in my driveway while R&R brakes and backing plates on a Nev-R-Lube equipped drum brake axle.

Of course lines, hoses and actuator required too.

If you'd like to see a pic send me PM with email. My 2007 has the Dexter 4 piston brakes.

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Old 11-03-2020, 05:56 PM   #4
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Hard to quantify but it would be substantial. Particularly onto the rear axle of the tow vehicle.

Saving grace is that the tow vehicle itself also transfers substantial weight to its front axle within itself. Keeping some reasonable balance on the tow vehicles axles.

This video may help visualize some of the dynamics going on. You can roughly understand the weight transfer by how much the vehicle squats at the front and rear axles.

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Old 11-04-2020, 10:12 AM   #5
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Hard to quantify but it would be substantial. Particularly onto the rear axle of the tow vehicle.

Saving grace is that the tow vehicle itself also transfers substantial weight to its front axle within itself. Keeping some reasonable balance on the tow vehicles axles........
Well that is a good point, and with WD perhaps keeps more weight on the trailer axle too. A bit complicated certainly, and obviously the CG height of the trailer affects the transfer too.
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Old 11-04-2020, 11:49 AM   #6
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The minimum percentage is fairly easy to reason through. Dexter biases the brakes to just stop about 95% of the weight rating of the axle without locking. In addition there is no reason to presume the trailer axles have a higher coefficient of friction than the tow vehicle. So at a minimum, all the tongue weight inertia is transferred to the tow vehicle. Next, the tow vehicle has antilock features so any torque added to the rear vehicle axle by the rotational inertia around the trailer brakes will be used to allow additional braking force. The calculation is complicated but we can say it is a minimum of 5-10% in a full emergency stop. So the minimum weight can be estimated at 15-30% depending on tongue and trailer weight.

If the trailer wheels do lock, then much more weight is transferred to the tow vehicle.

If there is sufficient interest, I can get the slide rule out but I would prefer not.
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Old 11-04-2020, 12:29 PM   #7
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If there is sufficient interest, I can get the slide rule out but I would prefer not.


Mine is a Pickett still have the belt holster and owners 1960 manual.
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Old 11-04-2020, 12:37 PM   #8
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Mine is a Pickett still have the belt holster and owners 1960 manual.
Slightly later vintage but have these in my desk drawer.....
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Old 11-04-2020, 01:08 PM   #9
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lol I don't think I can remember how to use one!
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Old 11-04-2020, 02:04 PM   #10
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With a break controller , we use it to manually put the AS brakes on when going down hill.

that reduces the TV load as well as reducing the As pushing the TV.

it does not have to be on 100%, just modulate it to regulate your speed.

Thus we don't really worry about braking force on downhill as we make the As do its own breaking

just use common sense on the roads i.e. downhill, rain, ice fog windy etc.
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Old 11-04-2020, 05:15 PM   #11
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Slightly later vintage but have these in my desk drawer.....
And I still use them. Love the HP reverse Polish Notation system. And of course a slide rule. I have my K&E from the good old days. Loved that thing and I earned a living with it for years.
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Old 11-04-2020, 05:34 PM   #12
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most of the weight would be pushing against TV if there's no trailer brakes. With working trailer brakes on, slim or none weight pushing the TV. it seems that way with my 19'
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Old 11-04-2020, 07:39 PM   #13
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And I still use them. Love the HP reverse Polish Notation system. And of course a slide rule. I have my K&E from the good old days. Loved that thing and I earned a living with it for years.


Ditto. My favorite gag at work was to loan the HP RPN calculator to someone and watch the fun. Still have my original K&E Deci-lon, itís scabbard and a copy of the book.
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Old 11-05-2020, 06:53 AM   #14
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Isn’t the weight that transfers to the tow vehicle the “tongue weight”?
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Old 11-05-2020, 07:11 AM   #15
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Just thinking, but if trailer brakes are working and applied harder than tv brakes, but not locking, does this not pull backwards from tv? You can stop tv with trailer brakes. If so how add to tongue weight? Just seems contrary to Newton. Be Safe.
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Old 11-05-2020, 08:10 AM   #16
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Just thinking, but if trailer brakes are working and applied harder than tv brakes, but not locking, does this not pull backwards from tv? You can stop tv with trailer brakes. If so how add to tongue weight? Just seems contrary to Newton. Be Safe.
What got me on this track was a recent instance where I had to "panic brake" so to speak with the trailer in tow. Stopped in time, and the trailer tires did not lock but were chirping so on the verge of lockup, and TV was at the point of activating antilock. The stopping distance was very obviously longer than our TV by itself even loaded for camping.

So perhaps with a dual axle there would be less transfer than with our single axle, but either way there is force applied to the TV (down at the hitch ball and forward). Same effect with our K2500 and a loaded 2 axle dump trailer BTW although never had to "panic brake" with that.

Be nice to have CarSim to model various combinations.

And yes, under lighter braking you can definitely have the opposite effect with trailer pulling back on TV depending on brake adjustment
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Old 11-05-2020, 08:45 AM   #17
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when going down a high, i use the brake controller to use its breaks. if i give to much force, i can feel the AS slowing the TV down. yes it has more force and the TV speed does slow down.

So yes, the As can slow down the TV, even going down a hill. I only have 2 wheels. 4 would be even stronger
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Old 11-05-2020, 02:52 PM   #18
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As you say, for casual braking, either the vehicle or the trailer can handle anywhere from 0-100% of the job required to slow the combination up to the point the braking force exceeds tire grip force. It all changes when all the brakes are applied simultaneously at maximum force especially when the vehicle includes adaptive brake controls as all modern vehicles do. There will be increased braking force applied particularly to the tow vehicle rear axle to take advantage of the additional grip afforded by tongue weight and torque created by the trailer brakes.

As I previously described in a max hard stop situation the tow vehicle will end up providing minimum of 15-30% of the trailer stopping force depending on trailer loading, tires,
and road conditions. More if the brake controller or trailer brakes are not configured correctly.
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Old 11-08-2020, 11:51 AM   #19
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Slide rule and HP 11c..

Pavlovian gurgle ...
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Old 11-09-2020, 08:37 AM   #20
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Slightly later vintage but have these in my desk drawer.....
Not to hijack this thread, but I have both of those too. Still use my HP 12C.

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