Payload affected by larger tires???

[huntindog]

Maybe it depends on the tt but I just pulled my last CAT scale sheets and the weight of my trailer axles remained the same with or without the wdh engaged. The only difference was between my front and rear tv axles.

The following was written by a well respected engineer, Ron Gratz who studied various hitches. I think he has since passed, but he did very detailed work.

Example assumptions:
TV wheelbase = 130”
TV rear axle to ball coupler = 65”
Ball coupler to TT axles = 200”
WD spring bar length = 30”
WD spring bar rear end load = 1000 lbs/bar = 2000 lbs total

How the WD hitch works:

Spring bar tensioner pulls UP on rear end of bar and DOWN on TT tongue. DOWN force of 2000 lbs on TT tongue adds a load of 300 lbs at TT axles.
This is calculated using ball coupler as the fulcrum: 2000x30/200 = 300.

Now, having added a load of 300 lbs at the TT axles, we must balance the TV/TT teeter totter. Using the TV’s rear axle as the fulcrum, to balance the 300 lbs at the TT’s axles we must add some load at the TV’s front axle.
The lever arm from the rear axle to front axle is 130”. The lever arm from the rear axle to the TT axles is 65+200 = 265”.
The required balancing load at the front axle is 300x265/130 = 611.54 lbs.

Or, we can calculate the reaction at the TV’s rear axle by treating the TV/TT as a lever with the fulcrum at the TV’s front axle.
The lever arm for the 300 lbs at the TT’s axles is 130+65+200 = 395”.
The lever arm for the rear axle is the wheelbase = 130”.
Since the TT axles are “lifting up” with a force of 300 lbs, this translates to an “uplift” at the rear axle equal to 300*395/130 = 911.54 lbs.

Summary of axle load changes:
TV front axle 611.54 lbs ADDED
TV rear axle 911.54 lbs REMOVED
TT axles 300.00 lbs ADDED

Now it is interesting to consider what happens at the hitch.

DOWN force of 2000 lbs on TT tongue adds a load of 1700 lbs at ball coupler.
This is calculated using TT axles as the fulcrum: 2000x170/200 = 1700.

The UP force of 2000 lbs on the rear ends of the spring bars produces an UP force of 2000 lbs at the hitch end of the spring bars.
The UP force of 2000 lbs minus the DOWN force of 1700 lbs on the ball gives a net UP force of 300 lbs at the hitch.
The vertical load on the receiver has been reduced by 300 lbs.
The vertical load transmitted through the ball has been increased by 1700 lbs.

It is interesting to note that TT weight and “tongue weight” do not enter into these calculations. The WD hitch does not distribute “tongue weight”. It simply removes load from the TV’s rear axle and distributes it to the TV’s front axle and the TT’s axles.

[Riverbug]

The following was written by a well respected engineer, Ron Gratz who studied various hitches. I think he has since passed, but he did very detailed work.

Example assumptions:
TV wheelbase = 130”
TV rear axle to ball coupler = 65”
Ball coupler to TT axles = 200”
WD spring bar length = 30”
WD spring bar rear end load = 1000 lbs/bar = 2000 lbs total

How the WD hitch works:

Spring bar tensioner pulls UP on rear end of bar and DOWN on TT tongue. DOWN force of 2000 lbs on TT tongue adds a load of 300 lbs at TT axles.
This is calculated using ball coupler as the fulcrum: 2000x30/200 = 300.

Now, having added a load of 300 lbs at the TT axles, we must balance the TV/TT teeter totter. Using the TV’s rear axle as the fulcrum, to balance the 300 lbs at the TT’s axles we must add some load at the TV’s front axle.
The lever arm from the rear axle to front axle is 130”. The lever arm from the rear axle to the TT axles is 65+200 = 265”.
The required balancing load at the front axle is 300x265/130 = 611.54 lbs.

Or, we can calculate the reaction at the TV’s rear axle by treating the TV/TT as a lever with the fulcrum at the TV’s front axle.
The lever arm for the 300 lbs at the TT’s axles is 130+65+200 = 395”.
The lever arm for the rear axle is the wheelbase = 130”.
Since the TT axles are “lifting up” with a force of 300 lbs, this translates to an “uplift” at the rear axle equal to 300*395/130 = 911.54 lbs.

Summary of axle load changes:
TV front axle 611.54 lbs ADDED
TV rear axle 911.54 lbs REMOVED
TT axles 300.00 lbs ADDED

Now it is interesting to consider what happens at the hitch.

DOWN force of 2000 lbs on TT tongue adds a load of 1700 lbs at ball coupler.
This is calculated using TT axles as the fulcrum: 2000x170/200 = 1700.

The UP force of 2000 lbs on the rear ends of the spring bars produces an UP force of 2000 lbs at the hitch end of the spring bars.
The UP force of 2000 lbs minus the DOWN force of 1700 lbs on the ball gives a net UP force of 300 lbs at the hitch.
The vertical load on the receiver has been reduced by 300 lbs.
The vertical load transmitted through the ball has been increased by 1700 lbs.

It is interesting to note that TT weight and “tongue weight” do not enter into these calculations. The WD hitch does not distribute “tongue weight”. It simply removes load from the TV’s rear axle and distributes it to the TV’s front axle and the TT’s axles.

Wow, that's an informative and comprehensive explanation. Thank you for sharing it.

[Ynot4me2]

The following was written by a well respected engineer, Ron Gratz who studied various hitches. I think he has since passed, but he did very detailed work.

It is interesting to note that TT weight and “tongue weight” do not enter into these calculations. The WD hitch does not distribute “tongue weight”. It simply removes load from the TV’s rear axle and distributes it to the TV’s front axle and the TT’s axles.
[/COLOR]

So like it's like I said, I think. Lol its been a long day. The wdh transfers weight from the rear axle of the tv to the front of the TV. Not to the tt axle. Now mind you, I have a smaller tt and on this particular weight, we were just returning from some warranty work (botch job from the dealer) so we weren't packed for a trip and I was still turning in my wdh.

[traveldawg]

The following was written by a well respected engineer, Ron Gratz who studied various hitches. I think he has since passed, but he did very detailed work.

Example assumptions:
TV wheelbase = 130”
TV rear axle to ball coupler = 65”
Ball coupler to TT axles = 200”
WD spring bar length = 30”
WD spring bar rear end load = 1000 lbs/bar = 2000 lbs total

How the WD hitch works:

Spring bar tensioner pulls UP on rear end of bar and DOWN on TT tongue. DOWN force of 2000 lbs on TT tongue adds a load of 300 lbs at TT axles.
This is calculated using ball coupler as the fulcrum: 2000x30/200 = 300.

Now, having added a load of 300 lbs at the TT axles, we must balance the TV/TT teeter totter. Using the TV’s rear axle as the fulcrum, to balance the 300 lbs at the TT’s axles we must add some load at the TV’s front axle.
The lever arm from the rear axle to front axle is 130”. The lever arm from the rear axle to the TT axles is 65+200 = 265”.
The required balancing load at the front axle is 300x265/130 = 611.54 lbs.

Or, we can calculate the reaction at the TV’s rear axle by treating the TV/TT as a lever with the fulcrum at the TV’s front axle.
The lever arm for the 300 lbs at the TT’s axles is 130+65+200 = 395”.
The lever arm for the rear axle is the wheelbase = 130”.
Since the TT axles are “lifting up” with a force of 300 lbs, this translates to an “uplift” at the rear axle equal to 300*395/130 = 911.54 lbs.

Summary of axle load changes:
TV front axle 611.54 lbs ADDED
TV rear axle 911.54 lbs REMOVED
TT axles 300.00 lbs ADDED

Now it is interesting to consider what happens at the hitch.

DOWN force of 2000 lbs on TT tongue adds a load of 1700 lbs at ball coupler.
This is calculated using TT axles as the fulcrum: 2000x170/200 = 1700.

The UP force of 2000 lbs on the rear ends of the spring bars produces an UP force of 2000 lbs at the hitch end of the spring bars.
The UP force of 2000 lbs minus the DOWN force of 1700 lbs on the ball gives a net UP force of 300 lbs at the hitch.
The vertical load on the receiver has been reduced by 300 lbs.
The vertical load transmitted through the ball has been increased by 1700 lbs.

It is interesting to note that TT weight and “tongue weight” do not enter into these calculations. The WD hitch does not distribute “tongue weight”. It simply removes load from the TV’s rear axle and distributes it to the TV’s front axle and the TT’s axles.

Thanks for both your posts. Nice, factual information with supporting documentation. I guess I had it wrong all these years. Your reference is quite helpful.

[huntindog]

So like it's like I said, I think. Lol its been a long day. The wdh transfers weight from the rear axle of the tv to the front of the TV. Not to the tt axle. Now mind you, I have a smaller tt and on this particular weight, we were just returning from some warranty work (botch job from the dealer) so we weren't packed for a trip and I was still turning in my wdh.

.1 Something is messed up with your weigh tickets. The GVW is off by 240# That number should be the same on both tickets.Whether WD is on or off.
.2 Re read what Ron wrote. It is NOT like you said

[Tigger1]

.1 Something is messed up with your weigh tickets. The GVW is off by 240# That number should be the same on both tickets.Whether WD is on or off.
.2 Re read what Ron wrote. It is NOT like you said

Agree. When I did my CAT scale weights, ticket#1 (WDH engaged) steer + drive axle was the same as ticket#2 (WDH dis-engaged) steer + drive axle.

Somehow his changed by 240# where it is also reflected in the Combined weight (12,040 vs. 11,800).

This is just a guess but it appears he stayed on the scales between weighs as there is just an 8 minute difference between tickets. I suppose it could be possible that by getting out of his truck to dis-engage the WDH then returning to the truck may have impacted the reading. Just a guess. With mine I pulled off, dis-engaged WDH, then back around and on again.

[Ynot4me2]

Agree. When I did my CAT scale weights, ticket#1 (WDH engaged) steer + drive axle was the same as ticket#2 (WDH dis-engaged) steer + drive axle.

Somehow his changed by 240# where it is also reflected in the Combined weight (12,040 vs. 11,800).

This is just a guess but it appears he stayed on the scales between weighs as there is just an 8 minute difference between tickets. I suppose it could be possible that by getting out of his truck to dis-engage the WDH then returning to the truck may have impacted the reading. Just a guess. With mine I pulled off, dis-engaged WDH, then back around and on again.

@huntingdog @traveldawg @Tigger1 @xrated
Looking at those sheets again, something is messed up. I did get off the scale to disengage the bars. That day was pretty quiet. And I swear that my 240 lbs butt was back in the truck. LOL
After re-thinking and re-watching that video I pulled some other scale sheets (same CAT scale) that I had. This was from a little trip we were doing and while I was still tuning the WDH. I was concentrating on the TV axle weight on the sheet as I was tuning the wdh.
These do show a difference of 120lbs on the trailer axle. The total is also off by 20lbs though. Must of been all that sweat from removing those bars.
We will be driving by that scale in Sept. for a 3 week trip and I wanted to hit again.
So I guess that wdh those move weight from the TV rear axle to the front tv axle and trailer axle.

[huntindog]

@huntingdog @traveldawg @Tigger1 @xrated
Looking at those sheets again, something is messed up. I did get off the scale to disengage the bars. That day was pretty quiet. And I swear that my 240 lbs butt was back in the truck. LOL
After re-thinking and re-watching that video I pulled some other scale sheets (same CAT scale) that I had. This was from a little trip we were doing and while I was still tuning the WDH. I was concentrating on the TV axle weight on the sheet as I was tuning the wdh.
These do show a difference of 120lbs on the trailer axle. The total is also off by 20lbs though. Must of been all that sweat from removing those bars.
We will be driving by that scale in Sept. for a 3 week trip and I wanted to hit again.
So I guess that wdh those move weight from the TV rear axle to the front tv axle and trailer axle.

It can be off 20 pretty easy as that is their unit of measure.

IE: It a vehicle weighs 5019 it could register as 5000 or 5020 and be within tolerance

[Bungy]

Maybe my old gray matter is failing me, but my logic circuits are not computing on this one.

I've read several comments referring to larger/heavier tires reducing the available payload, and I'm having a hard time understanding this line of thinking, so maybe someone can enlighten me.

The tires are not being carried on the truck, the truck is riding on the tires, so the available payload should not be affected, because payload is what's carried in/on the truck, yes/no/maybe?

Also, can someone explain to me how the WD/Anti-sway hitch puts some of the tongue weight back on the trailer, and what is the average amount of weight that goes back to the trailer, either in lbs or percentage.

Thanks!

Everything said so far is true however the weight police will only look at the load rating of your tires to determine if you’re overweight or not. Larger tires, say 18” vs 17” will have a higher load rating and may make you legal. Of course this has nothing to do with the GVWR on the door post.

[NB Canada]

Everything said so far is true however the weight police will only look at the load rating of your tires to determine if you’re overweight or not. Larger tires, say 18” vs 17” will have a higher load rating and may make you legal. Of course this has nothing to do with the GVWR on the door post.

I have never seen or heard of the “weight police” for a recreational vehicle
Would love to hear of what you have seen