Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×
 


Reply
 
Thread Tools Search this Thread Display Modes
 
Old 10-15-2014, 09:01 PM   #21
Rivet Master
 
rodsterinfl's Avatar

 
2006 25' Safari
St. Augustine , Florida
Join Date: Oct 2011
Posts: 2,670
Images: 10
Great read. Obviously you care enough to find out the details. I've read quite a bit and experimented with my own setup. What really helped me was The Curt hitch setup guide and the Ford advice on front suspension. As others stated, each setup gives different results. The eyeball method that Curt uses is pretty close. They suggest setting up a WD hitch with these simple steps:

On flat ground measure the height of each wheel well center from ground to top.

Hitch up the trailer without using WD and measure the wheel wells again. (this allows for a corrective reference)

Ford F150 advice on my year state that the front end must not ever be lower than without a load or, the first measure of the front wells.

Then, the adjustment begins. At 5.5 inches on my PP, I have all but 1/8" from original front wheel well position. So, the front really determines the amount of overall distribution capability. My first attempt at this method indicated at the CAT Scale that I was within 100 lbs of original front axle weight. I have since shaved that down to less loss than that. It does not gain weight on the front end which blows the distribution formula of thirds but I regain my original front-end weight by WD and distribute the bulk of the weight across trailer and rear of truck. This is the result, more or less, that I have gotten from two different hitch systems. The point is that even the simple wheel well measure, checked by the CAT Scale, provided me a fairly accurate method for setting the weight distribution. When I first started doing this I contacted a Curt representative concerned that I could not get the weight evenly distributed. He told me that no one does across all three axle points.
__________________
WBCCI 8653/AIR 60240
2022 Ford F150 PowerBoost Platinum w/7.2KW
rodsterinfl is offline   Reply With Quote
Old 10-15-2014, 09:45 PM   #22
4 Rivet Member
 
Livingston , Texas
Join Date: Dec 2007
Posts: 394
Exclamation

Quote:
Originally Posted by SteveH View Post
It's great to see some work done on the matter by the US DOT-NHTSA. However, I still believe not all setups are the same. A 1/2 ton pickup is different than a 3/4 ton, and they are both obviously different than a front wheel drive minivan. Each user must actually experiment with their own setup trying different adjustments to end up with the best driving, riding, and handling possible for their own rig.
Steve, I agree 1000% on this.

Many of the "rules" posted on this forum ignore too many important vehicle-specific factors.

Ron
Ron Gratz is offline   Reply With Quote
Old 09-12-2015, 06:54 PM   #23
4 Rivet Member
 
Livingston , Texas
Join Date: Dec 2007
Posts: 394
To avoid further hijacking, the following quoted text has been imported from Post #814 and Post #819 of the Equal-i-zer Hitch Thread.

Quote:
Originally Posted by Ron Gratz in another thread:
Quote:
Originally Posted by Inland RV Center, In
To remove weight from the front axle, will deem the steering wheel to become progressively useless, which in turn simply means your asking for a loss of control.
As I attempted to explain in response to Al's question about the weight of the WDH and bars:

Any mass added to a TV behind the rear axle will cause load to be removed from the front axle.
The added mass also will cause the TV's center of mass to move rearward.

The load on the front tires is reduced, but the distance from the front tires to the CM is increased.
Since the length of the moment arm (distance from axle to CM) is increased, the front tirescan cause the same amount of steering torque.

The steering ability of the front tires does not become progressively worthless, because the tires are exerting their force over a longer moment arm.

Now, if you're talking about load removed from the TV's front axle due to the downward force on the ball resulting from "tongue weight" -- you're talking about a completely different situation.
The reason it's different is because the "tongue weight" removes load from the TV's front axle, but doesn't cause a rearward movement of the TV's center of mass.

Ron
Quote:
Originally Posted by Al & Missy in another thread:
Quote:
Originally Posted by Ron Gratz

Now, if you're talking about load removed from the TV's front axle due to the downward force on the ball resulting from "tongue weight" -- you're talking about a completely different situation.
The reason it's different is because the "tongue weight" removes load from the TV's front axle, but doesn't cause a rearward movement of the TV's center of mass.
Ron
And this is the part i dont understand. Why is 900# of tongue weight any different from a 900# weight sitting on the hitch?

Taken to the limit, no matter how far aft the weight is, if it lifts the front tires off the ground, they won't provide any steering force. Not trying to be argumentative, just want to understand.

Al
Ron Gratz is offline   Reply With Quote
Old 09-12-2015, 07:05 PM   #24
4 Rivet Member
 
Livingston , Texas
Join Date: Dec 2007
Posts: 394
Al,

Yes, theoretically you can use tongue weight to lift the front tires off the ground.
If a TV has a 160” wheelbase and 4000# on the front tires, a 1000# tongue weight placed 640” (53.3’) behind the rear axle could completely unload the front tires.
Of course, you’d have to allow the tongue to drop a distance of 4 times the amount of front lift.

In reality, 1000# TW probably would remove only about 400# from the front axle. A 10% decrease in front axle load could be compensated by increasing the steering angle by about 10%.

But, the question is:
Why shouldn’t we just go ahead and use the WDH to replace all of the lost front-end load (or even replace more than 100% just for good measure)?
Doesn’t more load on the front tires make the front of the TV more responsive to steering input?
The answer to this second question is, “Yes”. However, more responsive steering is not necessarily a desirable objective.
Overly responsive steering (a.k.a. “oversteer”) easily can lead to loss of control.

When a TV and TT are rounding a curve, the pavement is exerting a force against the TT’s tires. That force is directed toward the inside of the curve.
Since the pavement force is acting rearward of the TT’s CG, the ball must exert a force (also directed toward the inside of the curve) to keep the TT in equilibrium.
According to Newton’s third law, since the ball is pushing the coupler inward, the coupler must be pushing the ball (and the rear of the TV) outward.

The outward force acting on the rear of the TV, tends to cause the TV to turn toward the inside of the curve. This tends to make the TV oversteer.
Simply placing a mass on the ball does not cause a lateral force on the ball, and doesn’t make the TV tend toward oversteer.

So, given that lateral force from the TT, when rounding a curve, will cause the TV to tend toward oversteer, why is it undesirable to use a WDH to add too much load back onto the TV’s front tires?
It is undesirable because adding load to the front tires (without moving the TV’s CG forward), also makes the TV tend toward oversteer.

Back in the 1970s, a scientific study conducted for the DOT-NTHSA (discussed in Post #3) demonstrated that increasing the load distribution degraded the tow vehicle understeer (made the TV tend toward oversteer) and reduced the speed for incipient jackknifing.
The study also concluded:
“---In this respect it was found that hook-ups resulting in a small hitch-low attitude (corresponding to 0 percent hitch load transfer to the front axle in conventionally sprung tow cars) is more desirable than a level attitude which provides approximately 25 percent hitch load transfer.---“

Circa 2010, a Letter to Editor contained the following:
---Specifically, recent full scale testing conducted by the SAE Tow Vehicle Trailer Rating Committee (and now published in SAE J2807), determined that the use of weight distributing hitch torque should be minimized. In fact they recommend that the Front Axle Load Restoration (FALR) not exceed 100% (100% means that the front axle weight is brought back, via weight distribution, to a weight equal to its “no trailer” condition).---"

Shortly thereafter, Ford indicated a desirable FALR for their trucks should be 50%. Other TV and hitch manufacturers then came forth with similar recommendations

Short story – TV and WDH manufacturers have concluded that allowing some load to remain removed from the front axle is preferable to restoring all of the load.

Ron
Ron Gratz is offline   Reply With Quote
Old 09-13-2015, 09:36 AM   #25
Rivet Master
 
Currently Looking...
Mantua , Ohio
Join Date: Jul 2005
Posts: 7,062
Blog Entries: 2
I got it. From my towing experience I agree totally as to not adding all the weight back to the front end.
xrvr is offline   Reply With Quote
Old 10-06-2016, 11:16 PM   #26
4 Rivet Member
 
Collyn's Avatar
 
Church Point , NSW
Join Date: Jul 2013
Posts: 261
FALR etc

I have not posted on this forum for a fair time as have been busy working on a (now 25 year!) project re a reasonably plain English guide to caravan & tow vehicle stability. It keeps getting too long.

Am currently attempting to get my head around the J2807 FALR performance metrics - as very applicable also to Australia (but where the WDH makers still push for 100% restoration - despite Cequant's recomendations).

There seems to be some confusion in that a few reports refer to 'reducing front tire weight' as increasing understeer' - that it cannot do. It can only decrease understeer.

That being so the suggested decrease appears to be such that a closer to neutral steer balance is achieved. What puzzles me though is that the then possible oversteer introduces a positive feedback loop - the last thing one needs in a close to infinite oversteer leading to jackknifing.

Or is it possibly that the full FALR introduces so much understeer that the desirable 0.4 g lateral cannot be achieved - and it is felt better that it should be (possibly enabling Dexter or AL-KO ESC to catch the rig if necessary).

I've read almost everything published re this since 1970 (particularly from Richard Klein) etc - and cannot see any other explanation.

(This is an increasing issue to us in Australia - where the caravan industry appears to have gone ape - with four tonne end-heavy megavans - with 5% tow ball mass - and towed by 2.5 tonne vehicles like a Toyota Hilux).

Would truy appreciate comment - particularly from Ron Gratz - whose comments I have been following for a long time.

My background is originally GM Applied Research (in the UK) mainly on suspension. I now write books and articles re all sorts of RV stuff (plus solar) but this area has always been my favourite.

I tend to speak metric and use esses where you use zeds (sorry zees?) but do understand pounds and mph! - no matter how archaic!

Collyn Rivers
Collyn is offline   Reply With Quote
Old 10-07-2016, 03:16 PM   #27
Vintage Kin
 
Fort Worth , Texas
Join Date: Nov 2006
Posts: 8,014
Images: 1
Weight Distributing Hitch Adjustment

The only expert around here (or on other RV forums) is Andrew Thomson of Can Am RV Centre, London, ON. Is a consultant to both Airstream and to the SAE committee on the above.

I'd recommend a thorough reading of his commentary at his website, on the Canadian magazine, RVLife, and his many posts at this site.

His refutation of "other than FALR" is solid. 31/1/2016 date at his website; Setting Torsion Bars.

Specifically, (and IMO) J2807 purposefully ignores whole classes of vehicles, both as potential TVs and wind loads on TTs versus the unrepresentative trailer employed.

Now, the differences between travel trailers here, in England or in Australia make for other problems in analysis.

I've enjoyed reading your contributions elsewhere and wish you well in your endeavor.
slowmover is offline   Reply With Quote
Old 10-07-2016, 08:54 PM   #28
4 Rivet Member
 
Collyn's Avatar
 
Church Point , NSW
Join Date: Jul 2013
Posts: 261
Quote:
Originally Posted by slowmover View Post
The only expert around here (or on other RV forums) is Andrew Thomson of Can Am RV Centre, London, ON. Is a consultant to both Airstream and to the SAE committee on the above.

I'd recommend a thorough reading of his commentary at his website, on the Canadian magazine, RVLife, and his many posts at this site.

His refutation of "other than FALR" is solid. 31/1/2016 date at his website; Setting Torsion Bars.

Specifically, (and IMO) J2807 purposefully ignores whole classes of vehicles, both as potential TVs and wind loads on TTs versus the unrepresentative trailer employed.

Now, the differences between travel trailers here, in England or in Australia make for other problems in analysis.

I've enjoyed reading your contributions elsewhere and wish you well in your endeavor.
Thank you for that - will follow it up.

I agree there is a major difference between UK and US practice, but to many Australian companies build product that is much closer to US than UK.

The theoretical basis however is the same.
Collyn Rivers
Collyn is offline   Reply With Quote
Old 10-07-2016, 09:33 PM   #29
4 Rivet Member
 
Collyn's Avatar
 
Church Point , NSW
Join Date: Jul 2013
Posts: 261
Have now read Andrew's refutation (and his associated writings) but he does not address the question that I was asking: what is the reason - in J2807 FALR -for reducing the WDH's effect on front-end mass (that thus reduces understeer.

I suspect it is to increase the ability to withstand higher g forces by ensuring the rig can follow a tighter radius (without incurring oversteer). If not, then what and why.

I have been reading Ron's postings in this area and they do reflect that of most (of the few!) people working in this field worldwide.

Collyn Rivers
Collyn is offline   Reply With Quote
Old 10-07-2016, 09:39 PM   #30
4 Rivet Member
 
Collyn's Avatar
 
Church Point , NSW
Join Date: Jul 2013
Posts: 261
Ron

Would you be kind enough to have a look at my postings re FARL - I would very much appreciate your comments. (Can be found by entering Collyn into the Search engine.

Kind regards
Collyn Rivers
caravanandmotorhomebooks.com

(in Australia)
Collyn is offline   Reply With Quote
Old 10-08-2016, 01:36 AM   #31
Vintage Kin
 
Fort Worth , Texas
Join Date: Nov 2006
Posts: 8,014
Images: 1
The simple answer is that -- after more than fifty years of success -- that "restricting" tow ratings to pickups enhances their desirability. Sales driven. (No different from other industries, alas).

Leave the tongue weight on the rear axle and it cancels out vehicles actually better suited to the job. Not to mention worse dynamics, overall.

One may as well examine the state of trailer suspensions. I believe you've compared them unfavorably to late 19th Century horse-drawn buggies which also used leaf springs. Shock absorbers are rarely even optional.

Not even a whiff of aerodynamic design (well understood before the 1930s), and hobbled farther by raised suspensions to accommodate the latest fad of "slide-outs". Worse in winds than their 1960s forebears.

Vehicles that once had adequate tow ratings (and still may in foreign countries) have had those dropped to token assignments. "Not tested".

The real world proves otherwise.

One could drive a pickup thru the omissions and obfuscations.


1990 35' Silver Streak
2004 555 Cummins
slowmover is offline   Reply With Quote
Old 10-08-2016, 07:30 AM   #32
Rivet Master
 
Vintage Kin Owner
N/A , N/A
Join Date: Sep 2012
Posts: 989
Images: 1
Quote:
Originally Posted by slowmover View Post
The only expert around here (or on other RV forums) is Andrew Thomson of Can Am RV Centre, London, ON. Is a consultant to both Airstream and to the SAE committee on the above.

I'd recommend a thorough reading of his commentary at his website, on the Canadian magazine, RVLife, and his many posts at this site.

His refutation of "other than FALR" is solid. 31/1/2016 date at his website; Setting Torsion Bars.

Specifically, (and IMO) J2807 purposefully ignores whole classes of vehicles, both as potential TVs and wind loads on TTs versus the unrepresentative trailer employed.

Now, the differences between travel trailers here, in England or in Australia make for other problems in analysis.

I've enjoyed reading your contributions elsewhere and wish you well in your endeavor.
Collyn,

A few points:

SlowMover is obviously a big fan of Andrew T. To state that he is the ONLY expert here or else where is obviously SlowMover's personal opinion and not necessarily accurate. I would surely read Andrew T's articles as they are very informative. Just don't take them as ground truth. There are many that disagree with his opinions based on their own many years of experience.

J2807 is SAE's standard for determining vehicle tow ratings. Everybody who is anybody has had input in setting up the standard. Its a set of well defined repeatable tests that allows (to some extent) apples to apples comparison of vehicles from different manufacturers. It tests pulling/stopping/cooling capacity of tow vehicles, their hitch strength, and their stability.

Testing is a means to verify the design. If the design says that a vehicle can tow 10,000#, we need an objective test to verify that. There is no point in testing a vehicle that is not designed for towing. Thats why auto manufacturers do not test the Camry's, Miata's, etc. but tests the pickups, SUVs, etc that have a substantial tow rating.
rostam is offline   Reply With Quote
Old 10-08-2016, 11:51 PM   #33
4 Rivet Member
 
Collyn's Avatar
 
Church Point , NSW
Join Date: Jul 2013
Posts: 261
Thank you

I have studied J2807 at length since it was first announced and understand that its intent is often misunderstood (and in some places possibly misrepresented).

The query I have is very specific.

It is why (by reducing the amount of understeer as a result of 100% FALR) is this seen as enhancing safety.

As I understand this part of J2807 full FALR results in the degree of understeer preventing a lateral acceleration of 0.4 g (it suggests 0.3 g).

Is it thus seen that it is better to limit understeer such that a higher g level is feasible?

This appears to be the only explanation. I was hoping that Ron might respond. I have read a fair number of his responses and understand his point of view.

If interested I have a piece in the new Australian Rvdaily.com in late October re AL-KO ESC, Dexter DSC and the lesser known IDC systems.

I do I fear share many of Slowmover's reservations re the state of trailer design. The EU is way ahead but does not build trailers of the size used in the USA.

Ours are somewhere inbetween - and with far too low nose mass (as low as <5%) and towed by vehicles often two thirds their weight. The physics relating to their behaviour is however just the same.

I have a large number of articles on my website re caravan & tow vehicle stability (but need to check this forum's rules re Links etc before mentioning that again).

Collyn Rivers
Collyn is offline   Reply With Quote
Old 10-09-2016, 05:34 AM   #34
Rivet Master
Commercial Member
 
Andrew T's Avatar

 
2019 27' Tommy Bahama
London , Ontario
Join Date: Aug 2007
Posts: 1,343
Hi Collyn

Below is a column I wrote about the SAE weight transfer recommendation. Certainly there may be something here that I don't understand but try as I might I cannot get the SAE recommendation to be stable.

If I can help feel free to call sometime and if you get to NA sometime feel free to come for a visit and we can do some test drives.

Andrew T

SAE J2807 Tow Rating Standard.
Setting The Torsion Bars:

In previous articles we discussed how to set your torsion bars properly. If you need a refresher here is a quick summary.


1) To set the torsion bars you need a level cement pad. To start, you want the trailer and tow vehicle in a straight line, disconnected, with the coupler ready to drop on the ball.

2) With the tow vehicle in position but disconnected use some masking tape and mark a height on all four corners of the tow vehicle’s bumpers, for example 22 inches, or whatever is appropriate for your tow vehicle.

3) Now that we know how the tow vehicle sits without the trailer, we want to determine the change in position when we connect. Generally the goal is to have the tow vehicle pushed straight down, so the front is pushed down the same amount as the rear.

4) Connect the trailer, do up the torsion bars and measure the change on the masking tape.

5) You will find that the tow vehicle will have been pushed down by the weight of the trailer. For example, the rear measurement may now be 20” instead of 22” but the front may have come up to 22.5”. In this case, you need to go up to the next link (adding tension to the torsion bars) and measure again.

6) However, you may find that the next link puts you into the opposite position where the front is pushed down 1” and the back stays even at the 22” mark. This means that the torsion bars are transferring too much weight forward.

7) If this is the case then you need a partial link. To do that, overlap two chain links and slide a ½” bolt through them. A ½” bolt is 1/3 of a link of adjustment so in some cases you will need 2 bolts to achieve the correct transfer.

8) Most tow vehicles will end between 21 ¼” & 21 ½” front and rear if you started with marks at 22”.

9) If you are setting up a new hitch the bars will wear in quite quickly. You’ll likely need to add a third of a link in 2-500 miles. You will need another third after another 500-1000 miles. You’ll probablyy feel the difference in the steering as this happens. After a while it just won’t feel as planted as it was after your initial set up. It’s fine to experiment 1/3 of a link at a time you should notice the difference in steering feel right away if it was the right or wrong change to make.

10) If you can’t get the weight to transfer to the front wheels without your torsion bars meeting the trailer frame then you don’t have enough reward angle on your ball mount, torsion bars too light, a hitch receiver that is too weak, or all of the above.

This is how we have configured hitches for the past 45 years. Because of these articles and internet searches, people with towing stability problems regularly seek us out. This is how we wind up helping them most of the time. A couple of hundred times every year we reconfigure a problem hitch that was installed elsewhere to these new settings. The difference is usually quite dramatic and customers are quite pleased. Now they don’t have to sell their trailer or buy a bigger truck.

The SAE has been working on a tow rating standard that they can use to better determine a vehicle’s tow rating. The standard will be better than nothing but it will still have many issues, the main one being that it is dependent on weight alone. The issue that concerns me most though is that they have come out with a recommendation on how to adjust torsion bars that in my experience is quite flawed.

What most vehicle manufacturers’ use for tow testing are enclosed cargo trailers with test weights inside. This gives the cargo trailers a low center of gravity, and most of them use torsion axle suspensions. Connect a tall RV trailer with a slide-out, leaf springs and no shocks and those handling tests are no longer meaningful. In a cross wind a tall RV trailer will behave much worse, however they did no testing on cross wind effects and really how could they? However most loss-of-control trailer accidents are the result of sudden wind changes.
The next barrier to effective testing is another SAE standard that we discussed in previous issues. Many of the vehicles being tested have hitch receivers that are too weak to transfer weight properly. If you cannot set up the hitch optimally how can you perform a good handling test? And most of the testing appears to be done with little or no rearward angle on the ball mount so the weight transfer on the tow vehicles is wrong. Without angle on the ball mount when turning, weight is taken off the front wheels and inside rear wheel and all dumped on the outside rear wheel. Last but not least the testing was done with the ball positioned well behind the bumper, and no effort was made to reduce overhang. The bottom line is that they never tested a truly dialed-in hitch system.
The next concern with J2807 is the handling tests themselves. I’m not certain how useful they are. One involves a test where traveling at highway speed, the steering wheel is snapped 180 degrees and immediately snapped back to the straight ahead position. The problem with this test is no correction for steering gear ratio or wheelbase. We talked about this in the article on steering. In a vehicle with a short wheelbase and a quick steering ratio this is a very violent maneuver, whereas in a long wheelbase vehicle with a slow steering gear it’s relatively relaxed.
J2807 is not the only time this method has been used. A few years ago Transport Canada set out to test the handling safety of 15 passenger vans. In this maneuver they used a steering robot to snap the steering wheel. This procedure removes the human equation but again they did not correct for steering ratio or wheelbase. The robot would seem like the ideal way to test; but is it? When in an emergency situation, as important as your steering input is the steering’s communication back to you. You can feel if the front tires are starting to plow or the back end is coming around. Take the human equation out of testing if you want, but in the real world people do the driving. A better test might be to flag down the first 20 everyday drivers and see how they perform.
The second SAE handling test is a steady state circle around the skid pad. As the G force increases the tow vehicle will start to go outside the circle, either the back end will break loose (oversteer) or the front tires will plow (understeer). Car companies like understeer. Now my own testing of this is on a delightful exit ramp with a downhill decreasing radius turn. What I find with my combinations is that the front end will almost always start to plow first but if you overcorrect which is the tendency then the back end will come around. If you just let it drift a little it pretty smoothly continues around the ramp drifting a slight bit off line. In the SAE test they kept breaking the back end loose. Which is to be expected since their hitch set up was unloading the inside rear tire and overloading the outside rear.
This combination of events led them to recommend a strange way of adjusting a weight distribution hitch. Instead of setting the hitch to push the tow vehicle down the same amount front and rear they use another method. Measure the height of the front of the tow vehicle. Drop the trailer on the ball without torsion bars. Measure again. Let’s say the front raises 2” then they want you to set the torsion bars so the front raises 50% from its solo position or in this case 1” higher than its solo position. This results in a considerable unloading of the steering axle. If you set your combination up this way it will be quite unstable at highway speeds especially when there is truck turbulence or cross winds.
In theory it would have a little more traction decelerating into low speed sharp turns. I have never seen an accident that was at all serious on a low speed sharp turn but there have been plenty due to loss of control at highway speed. After the SAE came out with this I thought possibly we’ve been wrong for 40 years. I tried setting up some combinations with their method and none of them were what I would consider stable at highway speeds. In fact most of the 200 trailers a year that we fix for people come in close to the SAE spec, usually due to a combination of weak receivers and improperly set ball mounts.
Before writing this column I wanted some more track testing just to check again that there was not something I was missing. I felt I should use a pick up as that is what the SAE used mostly in their testing. We used a ½ ton GM truck with a 34’ Airstream for testing. We tested it to the industry spec where the truck is pushed down evenly and to the suggested SAE spec. Two differences from the SAE testing were that our ball was close to the bumper as possible and we strengthened the stock hitch receiver. In their test the back axle lost traction with the industry specification. In the 100’ slalom we achieved 81 KPH with the hitch set to our spec, 81 KPH is really moving in the slalom. At the 6th cone the Airstream drifts sideways on all six tires which is no easy feat. In theory if the back tires were to break loose on the truck this is where it should happen when the trailer is sliding sideways but the truck stayed planted and slid very little if at all. When we tried the same speed with the SAE spec we made it to the second cone and had to give up the run due to lack of control. On the track there is a nice declining radius turn where we expected the SAE spec truck to do better but there was no speed difference to speak of, on both settings the front tires started to plow before the back wheels broke loose. Next we tried a steady state turn that took us down and then up a lip of asphalt as well as over several bumps with less sticky pavement. The SAE setting bounced more and felt less planted but again we could not measure any appreciable difference in speed. I think though most drivers would find it much easier with the industry spec.
If I were you at this moment I would be saying “who is this RV dealer schmuck who thinks he knows more than the Society of Automotive Engineers?” That’s a valid question. I have some advantages that the SAE does not have. I’m sure I’ve driven more combinations of trailers and tow vehicles with more hitch systems, tire changes etc. etc. than anyone you’ll ever meet. I don’t just wander down the road them either. I do quick lane changes, panic stops, and all manner of emergency maneuvers. I am also close to the real world customer. If a customer says they are having an issue, I’ll say let’s go for a ride and you can show me. We then get a good feel for what is really happening out there. We take most of our own vacations with trailers, so I always have something to experiment with. Additionally, we’ll have 7 to 10 different tow vehicles of our own that we use for pickups and deliveries. I can focus on RV trailers, while the SAE must worry about cargo, boat and horse trailers as well. The test track is a great tool and we spend a lot of time there but nothing is quite like real world testing, and that we have in spades. We have the opportunity to pay a lot of attention to something that no one else wants to be bothered with.
The other parts of SAEJ2807 are acceleration and cooling system tests. The combination at its rated weight needs to be able to accelerate from 0-60 in 30 seconds, unless it is a dual wheel truck, and then it can take 35. The cooling system test is done on a 10-mile long 6% grade in Arizona in 100+ degree heat at a minimum speed of 40 MPH, unless it is a dually. Then 35 MPH is magically ok.
One thing I asked for in the SAE standard was publication of the individual test results. This would allow people to find a vehicle that suits their individual needs better. For example, a Ford Edge crossover SUV may not have the acceleration of V8 F-150 with a V8, and it also might not do as well on the cooling system test but it would almost certainly be better in a handling test and be comparable stopping. If you are concerned about fuel economy and safety but not in a big hurry, and willing to back off a little in extreme heat, the Edge performs very well without compromising safety. For many it suits their lifestyle better. As it is, you only know the rating is lower but you don’t know why. Even then they would have to test the Edge to find its limits but since they only plan to rate it for 3500 they test to that and leave it there. Coincidently the Explorer which is built on a similar platform with the same drivetrain is rated to tow 5000 pounds but it is not nearly as good a tow vehicle. It sits higher, has a softer suspension, and a longer overhang on almost the same wheelbase.

I have the greatest respect for the SAE. What the auto industry has accomplished is nothing short of amazing, and the technologies reach far beyond the car industry. I think in this case the SAE has tried to take on something that should not be their job. Then whose job is it? I believe it should be the RV dealer. The dealer is the only one who sees the trailer, vehicle and hitch system and who also meets the driver and understands how he’s going to use the combination. But since many RV dealers are afraid to get involved over fear of lawsuits etc. the towing equation tends to be neglected. In fairness, if we didn’t have a 45-year track record I doubt we would do what we do either. The good news is you don’t have to take my word for any of this. It’s easy to experiment with your own combination. Set it up to both specs and try it each way and you can decide for yourself if the industry spec of the last 50 years is right or the SAE spec.
In the end, getting the right combination and making sure it is configured properly is often up to you. That’s why you need to look beyond tow ratings and solely weight, and focus on the core principles behind the design of the tow vehicle and the trailer. And of course never compromise your hitch set up!
__________________
Andrew Thomson
London, Ontario

"One test is worth a thousand expert opinions."
Tex Johnston, Boeing 707 test pilot
Andrew T is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
From the Noob desk: weight vs. weight distributing TINLOVE Hitches, Couplers & Balls 5 10-12-2014 10:10 PM
New single-arm weight distributing hitch bfk Hitches, Couplers & Balls 18 07-30-2006 09:45 PM
Weight distributing hitch choices Safari64 Hitches, Couplers & Balls 18 02-23-2006 11:12 AM
Blue Ox Weight Distributing Hitch Bill Price; Hitches, Couplers & Balls 5 02-28-2004 11:18 PM
Weight Distributing Hitch joshua32064 Hitches, Couplers & Balls 1 09-27-2003 07:16 AM


Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.



All times are GMT -6. The time now is 10:52 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.