Article about Tandem Torsion Axle Issues

[Semievolved]

Not really trying to cause trouble or angst but this article was very interesting to me and I hope of general interest as well.

https://mechanicalelements.com/torsi...dem-or-triple/

[oldwave]

Interesting article

[yangstyle]

That is an interesting article.
The diagrams with the car and trailer going over the bump are exaggerated I feel as the trailer is tongue low and if it was level depending on the size of the bump the back suspension probably would not leave the ground like shown.
The article would mean more to me if it had some data or testing from real world situations.

[C&G in FL]

Even though it makes jacking the trailer less convenient, I knew there was a reason I was glad my Escape has leaf springs with an equalizer! But I think (my opinion) the implication that tandem (or triple) torsion axles should not be utilized on a trailer is somewhat anal.

[rubicon327]

This is what Dexter says in their Applications Manual regarding dual and triple torsion axles if anyone is interested. Escape uses the #10.

[bborzell]

It would appear that the only factor that might cause the front wheel to assume an excess load because of the rear wheel leaving the road surface would be the front wheel using all of it’s available travel.

I wonder whether tandem torsion axles are designed with sufficient travel in the trailing (or leading) axle to accommodate those occasions when the wheel on the leading axle might lift the trailing wheel.

Do torsion axles offer significantly less travel than leaf springs by design?

[Perry Butler]

Took that with a grain of salt.

We did replace both axles in the first 7,000 miles, but that was because of a manufacturing defect, not because we keep driving over speed bumps. Our camper will last longer if we have a more supple axle. A stiffer axle will shake, vibrate, and rattle the camper causing other failures. Now at 27,000 miles our axles are fine, but I'd rather replace an axle than have our camper shake apart.

Sure, I wish Escape built their trailers with a walking beam torsion axle, but they don't. What fiberglass manufacturer builds with a walking beam?

There are many, many reasons we chose an Escape, but the axle was/is not even in the top 10. The Dexter axle is easily replaceable. I figure at around 100,000 miles we'll replace both axles, since they're kind of like shocks and can only flex so many times. YMMV.

Enjoy,

Perry

[escape artist]

Originally Posted by Perryb67

Took that with a grain of salt.

We did replace both axles in the first 7,000 miles, but that was because of a manufacturing defect, not because we keep driving over speed bumps. Our camper will last longer if we have a more supple axle. A stiffer axle will shake, vibrate, and rattle the camper causing other failures. Now at 27,000 miles our axles are fine, but I'd rather replace an axle than have our camper shake apart.

Sure, I wish Escape built their trailers with a walking beam torsion axle, but they don't. What fiberglass manufacturer builds with a walking beam?

There are many, many reasons we chose an Escape, but the axle was/is not even in the top 10. The Dexter axle is easily replaceable. I figure at around 100,000 miles we'll replace both axles, since they're kind of like shocks and can only flex so many times. YMMV.

Enjoy,

Perry

Hi: Perryb67... My Dr.'s advised me to shake the salt habit. The odd grain here and there doesn't hurt IMHO. When we changed from the 5.0 w/ a torsion axle to the 5.0TA w/ springs, equalizers and shackles I was concerned about towing the extra weight. After 6 yrs... I'm not so concerned. Alf
escape artist N.S. of Lake Erie

[JeffreyG]

Originally Posted by rubicon327

This is what Dexter says in their Applications Manual regarding dual and triple torsion axles if anyone is interested. Escape uses the #10.

This is it in a nutshell. The author of the original article describes the situation of one axle momentarily carrying additional weight as being "overloaded" which struck me as very wrong right from the outset. If two axles are rated to carry 3000 lbs apiece, then they are "overloaded" only when either axle is sitting with greater than 3000 pounds in a static, flat condition. Obviously the axle manufacturer anticipated that there will be both dynamic and situational static loads that are greater than the flat, static case. Encountering these cases is not an "overload".


To make an analogy, imagine a fighter aircraft has a maximum takeoff weight of "X". If this aircraft executes a maneuver, the wings may suddenly be bearing 4X, 5X, 6X or even more weight. That aircraft is not suddenly overloaded, it is doing what it was designed to do at the load limit.


If you put the design weight on a axle and slam into a pothole, it again is not "overloaded", it is bearing an extreme force it was presumably designed for when at the design load.

[Semievolved]

Originally Posted by rubicon327

This is what Dexter says in their Applications Manual regarding dual and triple torsion axles if anyone is interested. Escape uses the #10.

Thanks for posting this, it does address the question.
To me, the take home message is to do the best job I can ensuring the trailer is level front to back and to drive with extra care and slowly over speed bumps or other situations where unequal loading of the axles will occur.

I understand that leaf springs require a shock to damp the shocks.

I wonder if there's a great reason Escape and other RV makers don't opt for a single larger capacity axle to address this issue? With the load more concentrated on a single axle, the frame would likely need to be stronger through that area but it would avoid the unequal loading issue and also the extra tire wear that comes from the axle sets fighting each other on tight radius curves.



Maybe it's tire and wheel strength limitations that force them to use tandem axles.



It seems the Flexride suspension is quite nice and allows more adjust-ability than Dexter axles. That combined with what appears to be some quality control issues with Dexters that come and go, I wonder if Escape has considered switching over to Flexride?

[Brian B-P]

Originally Posted by JeffreyG

If two axles are rated to carry 3000 lbs apiece, then they are "overloaded" only when either axle is sitting with greater than 3000 pounds in a static, flat condition. Obviously the axle manufacturer anticipated that there will be both dynamic and situational static loads that are greater than the flat, static case. Encountering these cases is not an "overload".


To make an analogy, imagine a fighter aircraft has a maximum takeoff weight of "X". If this aircraft executes a maneuver, the wings may suddenly be bearing 4X, 5X, 6X or even more weight. That aircraft is not suddenly overloaded, it is doing what it was designed to do at the load limit.

Good point, but not quite true... as the quoted statement from Dexter explains, while bumps are part of design conditions, including momentarily having the entire trailer supported by one of two axles, having the entire trailer supported by one of three axles is not. This is comparable to pulling 3G's in an aircraft which is designed only for 2G's.

1. A trailer with one 3,000-pound-rated axle and a loaded gross weight of 3,000 pounds (on the axles) would be within the axle ratings, and would be properly equipped.
2. A trailer with two 3,000-pound-rated axles and a loaded gross weight of 6,000 pounds (on the axles) would be within the individual axle ratings, and would be adequately equipped.
3. A trailer with three 3,000-pound-rated axles and a loaded gross weight of 9,000 pounds (on the axles) would still be within the individual axle ratings, but would not be adequately equipped.

Anyway, there are no triple-axle Escapes, and the tandem axle loading situation has been considered. Early tandem-axle Escapes were lighter, and used Torflex units with the rubber reduced in length to suit a lower load (such as 2500 pounds) for better ride and control; however, the load capacity was still kept well over half of the allowed trailer weight due to the effect of bumps in a tandem configuration and non-level towing.

While it advises against even tandem use of these trailer suspensions, I think the article describes the issues and solutions well. An equalized suspension system would be better, but beam axles are worse than independent suspension and leaf springs are worse than rubber. The ideal solution is independent suspension, with the leading and trailing suspensions linked by using connected air springs... and no, that's not inexpensive or simple, so I'm not suggesting that Escapes should have that.

[Brian B-P]

Originally Posted by Perryb67

Sure, I wish Escape built their trailers with a walking beam torsion axle, but they don't. What fiberglass manufacturer builds with a walking beam?

None, of course (as I assume Perry is implying), because it would be more expensive, more complicated, uncommon... and would be unappreciated by almost all potential buyers.

[Brian B-P]

Originally Posted by Semievolved

To me, the take home message is to do the best job I can ensuring the trailer is level front to back and to drive with extra care and slowly over speed bumps or other situations where unequal loading of the axles will occur.

That makes good sense to me.

Originally Posted by Semievolved

I understand that leaf springs require a shock to damp the shocks.

It is true that a leaf spring by itself provides no damping of suspension movement, while the rubber used as the spring in a Torflex does provide damping. In a leaf-spring setup, only friction in the relative movement between the leaves of the multi-leaf spring pack provides any damping; that is generally considered adequate in basic trailers, but is not good enough for better trailers or for any motor vehicle, so separate hydraulic dampers (shock absorbers) are used as well. I added shock absorbers to a leaf-sprung travel trailer, and the improvement was noticeable.

On the other hand, even a rubber suspension like Torflex doesn't have enough damping to be ideal. The similar trailer suspensions sold in Europe have optional shock absorbers for better performance.

Originally Posted by Semievolved

I wonder if there's a great reason Escape and other RV makers don't opt for a single larger capacity axle to address this issue? With the load more concentrated on a single axle, the frame would likely need to be stronger through that area but it would avoid the unequal loading issue and also the extra tire wear that comes from the axle sets fighting each other on tight radius curves.

Maybe it's tire and wheel strength limitations that force them to use tandem axles.

There is no problem getting single axle suspension with sufficient capacity for any Escape, and wheels and tires to suit, and the frame loading isn't a problem. Escapes over 17' have tandem axles because buyers expect it, and value the additional stability that the scrubbing tires of a tandem provide. Reace did consider a single axle for the 19', and chose what he believed (my guess is correctly) would be preferred by buyers.

Originally Posted by Semievolved

It seems the Flexride suspension is quite nice and allows more adjust-ability than Dexter axles. That combined with what appears to be some quality control issues with Dexters that come and go, I wonder if Escape has considered switching over to Flexride?

The Flexiride design is inherently better in some ways than Torflex, but the only adjustment is in static height, and that doesn't address any of the tandem-axle issues. It also has shorter suspension arms (4.5" versus the 6" of a Torflex), which are not desirable in some ways. While Flexiride is generally highly regarded among rubber trailer suspensions, it is also typically more expensive... and a travel trailer buyer is unlikely to be willing to pay a premium for it.

[TTMartin]

Originally Posted by Semievolved

I wonder if there's a great reason Escape and other RV makers don't opt for a single larger capacity axle to address this issue?

Tandem axles tow better, they are less prone to sway. This is especially important with short wheelbase tow vehicles like SUVs that seems to be one of Escape's target markets.

Escape trailer's tandem axles is the reason I began looking at Escape trailers in the first place. Without Escape trailers having tandem axles I probably would have just purchased a Casita.

FWIW, IMO the author of that article is full of it and talking out his buttocks.

When towing a trailer with tandem torsion axles it is necessary to have the trailer level. However, regardless of the type or number of axles it is best to have the trailer level when towing it.



It has already been posted that the manufacturer states their torsion axles can deal with momentary overload in a tandem arrangement.

Also, keep in mind Escape trailers are far from being at the maximum weight limit of the axles to begin with. The GVW of the bumper pull trailer are 5000 lbs, dry weights are less than 4000 and together the tandem axles are rated for 7000 lbs.

[escape artist]

Hi: TTMartin... Thank you for stating the obvious so eloquently!!! I'm on a salt reduced diet so trying to control my take of grains. We hit a wash out towing the 5.0TA and didn't even upset the Rams alignment. The whiplash was so great that it split the battery case... but it was old too. Alf
escape artist N.S. of Lake Erie

[rubicon327]

Originally Posted by TTMartin

Also, keep in mind Escape trailers are far from being at the maximum weight limit of the axles to begin with. The GVW of the bumper pull trailer are 5000 lbs, dry weights are less than 4000 and together the tandem axles are rated for 7000 lbs.

Even the early 19's like ours which used 2300# axles for a smoother ride have not experienced any problems in 10+ years. I don't see any reports of failed or sagging axles. GVWR 4000#, 2510# dry weight (brochure), figure 3300# total on the axles going down the road (excluded tongue weight); axles together rated for 4600#. Don't anticipate any problems but if new axles are needed after 20-30 years it isn't hard or very expensive to bolt some new ones on.

[Iowa Dave]

Dance with the one that brought you. Both our Escapes have worked well with the factory axles on the terrain we are comfortable traveling. Vigilance, balanced tires and loading, regular maintenance and daily review of the mantra “Easy does it”, keeps me rolling along and not wasting time reading about why something I have that works doesn’t work.
Merry Christmas
Iowa Dave

[George Johnson]

There are a couple of additional things relating to axles and suspensions that haven't yet been mentioned on this thread.

First, with dual axles, you have the option of brakes on all four wheels. Much better heat dispersion on those long downhill grades.

Second, I have had several long haul truckers tell me that when equipped with linked dual axles, such as walking beams or equalized leaf springs, the shocks of rough roads transmitted to the load in the vehicle are greatly reduced.

There is also the additional safety factor of much better control of the trailer in the event of a blowout of one of the trailer's tires, an unfortunately common occurrence with the cheaply made (but not inexpensive!) ST tires commonly used on RV trailers.

[Centex]

If anyone wants to do more reading about 'walking beam' and 'torsion axles' there's this article and the others linked within it (all from the same source as the article linked in the OP above).

Case Study: Torsion Axle Walking Beam Suspension (Part 1)

Case Study: Suspension Engineering with Twin Torsion Axles – Part 2

[Brian B-P]

Originally Posted by George Johnson

Much better heat dispersion on those long downhill grades.

You also need brakes on all four wheels just to match the braking performance of brakes on the two wheels of a single axle. While some jurisdictions may allow brakes on just one axle of a trailer which requires brakes, brakes on both axles may be required and they are always provided on Escapes.

Originally Posted by George Johnson

Much better heat dispersion on those long downhill grades.

If you are dragging the trailer brakes down long downhill brakes you need to stop doing that and use engine braking properly, no matter how many crude drum brakes you have on the trailer. Even modern disk brakes on motor vehicles should not be used to control descent speed on an extended grade.