Am I getting enough of a truck?

[BobKilmer]

I thought we were debating towing perfomance? Your braking example goes out the window with a trailer in tow.
when braking hard the pin weight increases dramatically pushing the rear tires into the road.

I didn't raise the difference in braking of SRW vs DRW. You did. I believe there is no real difference between the two.

I doubt the braking is going to behave as you described. There isn't really a weight transfer happening during braking, it is accelerations changing the forces on the vehicles. Any force from the RV deceleration is going to be forward, not down, and this will still load the front suspension of the TV, not the rear suspension.

[Tony_in_AZ]

A photo of the frame sticker on my 2021 F350 4x4 dually long bed truck. I thought it was interesting.

[powerscol]

I didn't raise the difference in braking of SRW vs DRW. You did. I believe there is no real difference between the two.

I doubt the braking is going to behave as you described. There isn't really a weight transfer happening during braking, it is accelerations changing the forces on the vehicles. Any force from the RV deceleration is going to be forward, not down, and this will still load the front suspension of the TV, not the rear suspension.

It appears you have never studied engineering or taken a dynamics class. @huntindog is correct especially for a 5th wheel. The king pin will rotate down increasing the load and depending on the hitch location effect front steering geometry. Yes it also shifts the weight forward as well. Unfortunately the trailer front axle lifts at the same time which is the result of the load shift on the equalizer. Lots of videos on this ( check MorRyde web page) showing the front wheel lockup.

Now as to the path of the load, yes the load on a SRW and DRW passes through the springs to the axle. The axle on the DRW spreads the load out wider and the springs are stiffer. Also I believe you will find the frame on a dually is slightly different than the SRW with different stuffier springs (this changes the load transfer weight) and mounting points, slightly outboard from the SRW due to the Dana 80 axle over the smaller Sterling axle. Other brands may be different. This is a good topic to search.

Now of note, I don't think the OP has been back to comment on anything since their first post I still believe he needs more truck

Also there was a post of folks towing a 150 series with a dually. I did that for a while after downsizing my trailer. I did not need a big unit anymore, and used the dually as I normally wood. Also some folk tow other trailers for work etc. Some like the extra stability of a dually too.

And there is nothing wrong with having too much truck. I have been an engineer too long to gamble on the safety of my family, to save a penny on a smaller truck.

Before I ordered my new truck I even considered a F450 for the turning radius and possible future trailer. I like to stay away from glamping (full hookups) and like the state and local parks and even the Nation Parks, all of which have average max unit length of about 35' and have tight sites, many unchanged fir over 40 years, and yes I have been towing various RV's that long or longer.

[BobKilmer]

It appears you have never studied engineering or taken a dynamics class. @huntindog is correct especially for a 5th wheel. The king pin will rotate down increasing the load and depending on the hitch location effect front steering geometry. Yes it also shifts the weight forward as well. Unfortunately the trailer front axle lifts at the same time which is the result of the load shift on the equalizer. Lots of videos on this ( check MorRyde web page) showing the front wheel lockup.

Now as to the path of the load, yes the load on a SRW and DRW passes through the springs to the axle. The axle on the DRW spreads the load out wider and the springs are stiffer. Also I believe you will find the frame on a dually is slightly different than the SRW with different stuffier springs (this changes the load transfer weight) and mounting points, slightly outboard from the SRW due to the Dana 80 axle over the smaller Sterling axle. Other brands may be different. This is a good topic to search.

Now of note, I don't think the OP has been back to comment on anything since their first post I still believe he needs more truck

Also there was a post of folks towing a 150 series with a dually. I did that for a while after downsizing my trailer. I did not need a big unit anymore, and used the dually as I normally wood. Also some folk tow other trailers for work etc. Some like the extra stability of a dually too.

And there is nothing wrong with having too much truck. I have been an engineer too long to gamble on the safety of my family, to save a penny on a smaller truck.

Before I ordered my new truck I even considered a F450 for the turning radius and possible future trailer. I like to stay away from glamping (full hookups) and like the state and local parks and even the Nation Parks, all of which have average max unit length of about 35' and have tight sites, many unchanged fir over 40 years, and yes I have been towing various RV's that long or longer.

You really should check your facts before making personal comments. I have degrees in Math, Physics, and Engineering. And 40 years of engineering experience designing and building complex, real world, aircraft and systems. I will match my engineering skills and experience against anyone. If you would like I will exchange resumes.

That experience, and the multiple dynamics classes I HAVE taken, are why I can say that huntindog is wrong. In fact, if you look at your comments, they indicate exactly what I said will happen. The load will transfer primarily to the front axles of the truck. If you draw a static and dynamic load diagram you will see that.

As for the wider body, I guess you didn't see the post just before yours. The F-350 Dually frame is the same as the F-350 SRW and F-250 SRW frame. The frame load paths are the same. Stiffer springs don't change the load path or the actual weight transferred.

For the load paths, again draw a static and dynamic load diagram. The torque and weight from the hitch is following a common load path on both the SRW and DRW path down to the axle. For there to be a difference in SRW vs DRW, there would have to be one of the following happening:
1) The axle is flexing to the point it can be felt in the truck. Doubtful any axle could take this much flex.
2) The tire tread is compressing to the point of being felt in the truck. Extremely doubtful. I would expect this to be accompanied by a squealing noise similar to cornering too hard.
Unless those are happening weight to the axle is the same as weight to the ground. Being wider doesn't help until there is enough force to try to lift a tire. Then being wider helps.

The one valid point you make is the difference in spring weights. That is the one difference that matters under normal conditions. I believe that the reported improvement for towing performance that most people talk about is due to this factor. I realized that long ago and I offset the added load of towing with my air springs. It doesn't change my ratings, but it allows me to use the full towing capability without any concerns about hitting my overload springs.

You are also correct about there not being anything wrong with having too much truck. But there is something wrong about confusing preference versus requirements, or making subtle jabs about safety wrapped in moneysaving comments.

[powerscol]

You really should check your facts before making personal comments. I have degrees in Math, Physics, and Engineering. And 40 years of engineering experience designing and building complex, real world, aircraft and systems. I will match my engineering skills and experience against anyone. If you would like I will exchange resumes.

That experience, and the multiple dynamics classes I HAVE taken, are why I can say that hutindog is wrong. In fact, if you look at your comments, they indicate exactly what I said will happen. The load will transfer primarily to the front axles of the truck. If you draw a static and dynamic load diagram you will see that.

As for the wider body, I guess you didn't see the post just before yours. The F-350 Dually frame is the same as the F-350 SRW and F-250 SRW frame. The frame load paths are the same. Stiffer springs don't change the load path or the actual weight transferred.

For the load paths, again draw a static and dynamic load diagram. The torque and weight from the hitch is following a common load path on both the SRW and DRW path down to the axle. For there to be a difference in SRW vs DRW, there would have to be one of the following happening:
1) The axle is flexing to the point it can be felt in the truck. Doubtful any axle could take this much flex.
2) The tire tread is compressing to the point of being felt in the truck. Extremely doubtful. I would expect this to be accompanied by a squealing noise similar to cornering too hard.
Unless those are happening weight to the axle is the same as weight to the ground. Being wider doesn't help until there is enough force to try to lift a tire. Then being wider helps.

The one valid point you make is the difference in spring weights. That is the one difference that matters under normal conditions. The reported improvement on towing performance is due to this factor. I realized that long ago and I offset the added load of towing with my air springs. It doesn't change my ratings, but it allows me to use the full towing capability without any concerns about hitting my overload springs.

You are also correct about there not being anything wrong with having too much truck. But there is something wrong about confusing preference versus requirements, or making subtle jabs about safety wrapped in moneysaving comments.

Not going down the rabbit hole

Safe travels

[huntindog]

I didn't raise the difference in braking of SRW vs DRW. You did. I believe there is no real difference between the two.

I doubt the braking is going to behave as you described. There isn't really a weight transfer happening during braking, it is accelerations changing the forces on the vehicles. Any force from the RV deceleration is going to be forward, not down, and this will still load the front suspension of the TV, not the rear suspension.

Not if your trailer brakes are working as they should be.

[Scott'n'Wendy]

Properly set up brakes will cause some but not huge upward/downward, forward/backward forces on the KP. Opinion...no data to back that up...lol
Typically, 70% of the braking of the TV is done by the front brakes. If there is extra pressure on the KP either upward or downward, it will change the point in which the anti-lock moderates the pressure in a panic stop.
IMO, the safety discussion is just personal. If you are towing within the rated payload of your TV, or the one you are about to buy, you are lots safe. How you drive is probably a bigger factor in safety..lol

[Calbar]

Properly set up brakes will cause some but not huge upward/downward, forward/backward forces on the KP. Opinion...no data to back that up...lol
Typically, 70% of the braking of the TV is done by the front brakes. If there is extra pressure on the KP either upward or downward, it will change the point in which the anti-lock moderates the pressure in a panic stop.
IMO, the safety discussion is just personal. If you are towing within the rated payload of your TV, or the one you are about to buy, you are lots safe. How you drive is probably a bigger factor in safety..lol

Very well said.

Rob

[LMagelitz]

After not seeing this for a couple of days, all I can say is, “the poor OP got more than he bargained for.” Maybe the OP should find a couple buddies, one with an SRW and one with DRW and decide for himself. That would be better than trying to gather anything useful from a bickering tirade between the “I have been driving for 150 years and have 42 doctoral degrees” from the SRW-only OR the DRW-only crowd.

When deciding between two important things, I’ll usually weight the opinions of those that have had each “thing” more than those that have only had one of the “things.” That is where the “experience” piece of the “tow experience” comes from.

Don’t bother flaming this response, cause I’m out. Geez…..

[Second Chance]

Thread closed.

Rob