What it Really Weighs

[Barb&Tim]

Originally Posted by harveyrv

I am considering replacing my 3500# axle with a 4400# rated axle.

Hmmm:

harveyrv, have you considered a possible downside of this being a much harsher ride for your TM?

For Torflex axles, Dexter seems to recommend axle choices that puts the best ride performance when the torsion bar is at or near horizontal when trailer is a rated load.

If i am reading this correctly, at higher torsion bar angles, less torque is applied to the torflex axle and more torque is applied to the tires/wheels.

Tim

[Mr. Adventure]

Originally Posted by Barb&Tim

Hmmm:

For Torflex axles, Dexter seems to recommend axle choices that puts the best ride performance when the torsion bar is at or near horizontal when trailer is a rated load.

If i am reading this correctly, at higher torsion bar angles, less torque is applied to the torflex axle and more torque is applied to the tires/wheels.

Tim

The axle spindle is mounted on an arm that swivels in the same direction as tire rotation, so the softest ride would be when the arm is horizontal (no torque is applied to the wheels). The reference manual I posted earlier in this thread says that Dexter sells axles with different starting angles, so you could work at this a bit if you were in the trailer building business.

[scrubjaysnest]

Thanks MR. A for the link to the aps manual.


From it I would say the GAWR for the 2011 2720 SL is 3500# not the 3640# TM uses. The lowest rating I can find on our TM is the 3500# stamped on the axle. The wheels I don't know about because I have been unable thus far to find a rating. The tires, Goodyear Marathons, are 2540# at 65 psi per the side wall.

I'm with harveyrv on the 4400#. It looks like the better way to go. That said I'm sure there are other limiting factors like the frame of tongue. It also appears the 2720SL has the potential to be loaded much heavier on the street side than the curb side. Up to 32 gals on water, refrig plus contents, dry weight of water heater, and the battery(s).

[Barb&Tim]

Originally Posted by scrubjaysnest

I would say the GAWR for the 2011 2720 SL is 3500# not the 3640# TM uses.

I have disagree with your conclusion. I stand by my previous explanation of why the GAWR is 3640#.

Tim

[Wavery]

Originally Posted by Mr. Adventure

From Dexter Axle, Definition of Terms, P3:

"GAWR - Gross Axle Weight Rating
The value specified by the vehicle manufacturer as the load carrying capacity of the axles in a system, as measured at the tire-ground interfaces. This includes the wheels and tires."

Dexter applications Manual:
http://i.b5z.net/i/u/1080235/f/Appli...te_Catalog.pdf

You may want to read the part titled "Load Ratings". It explains why they defer to the trailer manufacturer for the GAWR........ The "LOAD RATING" is stamped on the axle and simply stated......."load" is the weight that Dexter says the axle can carry on the mounting brackets..

[Mr. Adventure]

Originally Posted by scrubjaysnest

Thanks MR. A for the link to the aps manual.

From it I would say the GAWR for the 2011 2720 SL is 3500# not the 3640# TM uses. The lowest rating I can find on our TM is the 3500# stamped on the axle. The wheels I don't know about because I have been unable thus far to find a rating. The tires, Goodyear Marathons, are 2540# at 65 psi per the side wall.

I'm with harveyrv on the 4400#. It looks like the better way to go. That said I'm sure there are other limiting factors like the frame of tongue. It also appears the 2720SL has the potential to be loaded much heavier on the street side than the curb side. Up to 32 gals on water, refrig plus contents, dry weight of water heater, and the battery(s).

The GAWR is the rating on the vehicle label plate. It's measured on a scale and includes the wheels and tires. The "Load Rating" Harvey points out is useful in keeping apples to apples comparisons while you're contemplating an axle swap, as he is at this moment. You have no practical way to measure your axle loads at the point of contact between the axle and the frame, so therefore, the Load Rating stamped on the axle is not otherwise going to be a relevant term.

These are static loads. Dynamic loads are much higher as we encounter the bumps in the road. People with extreme bumps are the ones exploring the edge of the envelope. It's all OK, though because The Dexter people build a lot of trailer axles and they know a lot about these things.

I'd expect the frame to not become a factor within the TM family of axles if the size of the frame members turns out to be the same on all TM's, an easy thing to verify. The load at the hitch ball is going to be well short of the loads at the axle attach points (~600# +/- wdh loads vs 1750 on each side (2500 in the 3023). The bending swing hitch issue explored on another thread (http://www.trailmanorowners.com/foru...8063#post78063) is a possibly non-trivial concern for those with swing hitches, since it appears to establish the swing hitch connection point as the frame's weakest spot (if I had a swing hitch, I would be periodically checking for paint cracks at welds and looking for signs of bending in this area).

[scrubjaysnest]

Originally Posted by Barb&Tim

I have disagree with your conclusion. I stand by my previous explanation of why the GAWR is 3640#.

Tim

Since it is only 140# and less then 10% it really isn't a big deal but per the RV industry and Dexter we only can go with what they define which is the weakest link. And yes you are correct the final defining point per Dexter and the RV industry is the manufacturer of the RV even though they both define it slightly different.

[Mr. Adventure]

The Adventuremobile has a V6 with 220hp. For perspective:

The 37 foot Winnebago I used to own had a Ford V10 engine with 310hp towing a small car and a tow dolly for a total of about 26000# combined weight on the road in adventure mode. On one grand adventure a few years ago, we crossed the Continental Divide 18 times in 5 different states without any power problems.

In round terms, the Highlander in combo with the TrailManor has about 2/3 of the power and 1/3 of the weight we had with the motorhome (and almost 3 times the gas mileage, too). In other words, the TrailManor gives me more than double the power to weight ratio versus my previous RV setup.

[T and C]

Originally Posted by Mr. Adventure

The Adventuremobile has a V6 with 220hp. For perspective:

The 37 foot Winnebago I used to own had a Ford V10 engine with 310hp towing a small car and a tow dolly for a total of about 26000# combined weight on the road in adventure mode. On one grand adventure a few years ago, we crossed the Continental Divide 18 times in 5 different states without any power problems.

In round terms, the Highlander in combo with the TrailManor has about 2/3 of the power and 1/3 of the weight we had with the motorhome (and almost 3 times the gas mileage, too). In other words, the TrailManor gives me more than double the power to weight ratio versus my previous RV setup.

Mr. Adventure,

I think the power to weight ratio of an RV is more complex than that. The maximum horsepower rating on any motor is at a specific rpm. If the optimum rpm for a specific engine is 5000 rpm, and that engine is only turning at 3500, it is not developing its full designed horsepower rating at that moment. Therefore the actual, (versus rated) power to weight ratio is actually constantly changing as you drive.

Tom

[Mr. Adventure]

Originally Posted by T and C

Mr. Adventure,

I think the power to weight ratio of an RV is more complex than that. The maximum horsepower rating on any motor is at a specific rpm. If the optimum rpm for a specific engine is 5000 rpm, and that engine is only turning at 3500, it is not developing its full designed horsepower rating at that moment. Therefore the actual, (versus rated) power to weight ratio is actually constantly changing as you drive.

Tom

"Optimum" and max horsepower are at different places on the power curve. The purpose of all those gears in the transmission is to keep the engine in a productive range. The purpose of an automatic transmission is so that we don't have to do math to find the right one.

But you're absolutely right: the Ford truck V10 engine is designed to have a broad power curve like a diesel, with lots of pulling power across a wide rpm range (it has 150+hp from 2500 to 4500rpm, and most of that range is over 200hp). It's purpose is probably not to impress us so much with it's peak horsepower as it's value in a truck engine. But it looks like the Toyota 3.5l puts out 150 hp rising to 220hp while going from about 3700rpm to over 6000rpm, which isn't shabby (torque is in the 200ft-lb range vs a max of 410ft-lb for the V10) (the data is from people trying to sell performance-ware:Toyota http://www.knfilters.com/dynocharts/69-8611_dyno.pdf and Ford V10 http://www.gearvendors.com/images/f68.gif). So, we currently have half the torque and 1/3 of the weight as my motorhome experience, netting a 50% improvement. We're not underpowered for towing a TrailManor.

What actually counts is having enough power in a range where you can use it, and the more pounds you haul, the more power you need and the more fuel you use. It's possible that I would own a different tow vehicle if I towed over the pass and through the Eisenhower tunnel every week, but I'm not worried about visiting there again someday.