Audi RSQ8 towing 27' Globetrotter... Are we nuts or in love?

[BayouBiker]

Originally Posted by matthewk

Trailer has its own brakes. This shouldn't ever happen if the gain is properly set.

Matthew. Under ideal braking, accounting for normal trailer braking conditions, the trailer will only stop the dynamic load on the trailer axles when brakes are applied. There is no good reason to assume the trailer axle friction coefficients are superior to the tow vehicle, logic suggests just the opposite.

Ok so this means that the tow vehicle will be required to hold back the tongue weight plus the dynamic torque applied to the tongue due to trailer stopping force. In an emergency this will be at least 20% and could climb to 25% of the trailer when the trailer brakes are at their stopping limit. Applying trailers brakes harder will only cause the tires to lock and then even more stopping force is transferred to the tow vehicle, 50% or more. Dexter is aware of this and attempts to bias the brakes so they will not lock when the axles are 90-95% or more loaded. This helps prevent inexperienced drivers from causing significant issues by setting the bias too high.

[BayouBiker]

Originally Posted by pteck

No disrespect and I admire your passion.

There is an fundamental understanding you have that is not correct, that you have voiced multiple times in various threads. The primary concern with overhung hitches is not oversteer as you assume. It's actually just the opposite - understeer.

Intuitively, putting a weight at the rear axle increases rear axle traction. Put it on the rear axle in an overhung manner adds to that effect with reduced front axle traction. Understeer, and loss of directional control, is a primary limiting factor. In fact, the main J2807 tests are for understeer against different FALR settings in its Combination Handling Requirements when establishing vehicle tow limits. Among damping factors and others.

pteck, thanks for your concern. Your intuition about the static torque effects are spot on, but you failed to address the effect of lateral forces from trailer inertial moment. Unfortunately for travel trailers in particular, this effect is much greater than the effects you did address. There are many great articles and papers online that discuss this in detail. Take a closer look at the SAE J2807 combined handing test. The one addressing Understeer gradient is expressed that way because the convention is to express it as degrees of understeer per g of lateral force. Understeer is positive, oversteer is negative and the test requires a gradient greater than zero.

Thought you might want to know before you continue your thoughts on oversteer. The resulting jackknife due to loss of control in an accident is not the main root of concern as you keep alluding to.

Static instability (positive feedback oversteer) and dynamic instability (amplifying sway) both end in out of control oversteer leading to jackknife and likely rollover.

Severe understeer can be an issue also, but it generally forces undesired drift into the next lane or the guard rail. Not nice.

Have a look at some articles and come back to me if you still believe I have this wrong.

[Sailorguy]

There is no doubt about it, your Audi isn't cut out to Tow a 27 foot GT. If your heart is set on an Audi (nice vehicle) I would recommend you consider a smaller AS, say the 22 Caravel!

[Lafitte]

^
what he said .....

[Collyn]

I am interested to know if forum members actually weigh their travel trailer payloads - or estimate that weight.

Until recent years a major US tyre association published a yearly report on a vast number of actually measured laden trailers. About 80% were well over their maximum - many even beyond the tyres allowed maximum.

Australian police do similar checks - with almost findings - about 80% are over. One (that had a rated payload of about 500 lbs) was 2000 lbs!.

Collyn

[dznf0g]

Originally Posted by Collyn

I am interested to know if forum members actually weigh their travel trailer payloads - or estimate that weight.

Until recent years a major US tyre association published a yearly report on a vast number of actually measured laden trailers. About 80% were well over their maximum - many even beyond the tyres allowed maximum.

Australian police do similar checks - with almost findings - about 80% are over. One (that had a rated payload of about 500 lbs) was 2000 lbs!.

Collyn

I do. Scales every couple years and a very elaborate spreadsheet where every pound, based on tv or trailer location is accounted for. Took me several years to perfect it, but it is very accurate.

[gator.bigfoot]

Originally Posted by Collyn

Isaac Newton.
Collyn

I'll believe the guy who sets up hundreds of trailers every year and has setup just about any vehicle and trailer out there. The guy who tests the combination for stability and handling and a bunch of "armchair engineers". Seems to me these armchair engineers just want to get recognized for knowledge they don't have. Book knowledge and experience are 2 different things in my world. I meet people like you every day and in my mind they should have found a different career.

[BayouBiker]

I don't see installers do properly designed towing stability tests for sway or oversteer with both the vehicle and the trailer loaded with gear or equivalent weights as they would be for camping. The result is the customer towing with a vehicle over the manufacturers ratings does not know if the combination will remain in control in unusual circumstance outside the tested conditions.

[pteck]

Originally Posted by BayouBiker

pteck, thanks for your concern. Your intuition about the static torque effects are spot on, but you failed to address the effect of lateral forces from trailer inertial moment. Unfortunately for travel trailers in particular, this effect is much greater than the effects you did address. There are many great articles and papers online that discuss this in detail. Take a closer look at the SAE J2807 combined handing test. The one addressing Understeer gradient is expressed that way because the convention is to express it as degrees of understeer per g of lateral force. Understeer is positive, oversteer is negative and the test requires a gradient greater than zero.



Static instability (positive feedback oversteer) and dynamic instability (amplifying sway) both end in out of control oversteer leading to jackknife and likely rollover.

Severe understeer can be an issue also, but it generally forces undesired drift into the next lane or the guard rail. Not nice.

Have a look at some articles and come back to me if you still believe I have this wrong.

Fair and perhaps its semantics. I'm not forgetting lateral forces.

I think where we differ is that traditionally, oversteer is defined by sideslip at the rear axle. That's not what's going on at least in the initial loss of control. It's actually loss of traction at the front axle due to the overhung hitch forces. Less traction equals less positive directional control. To your point, lateral force from an overhung hitch can also influence the yaw of the vehicle, and without enough positive front axle control, will ultimately create a jackknife situation - because the tow vehicle doesn't have enough front axle traction to maintain control. Whether we want to call that oversteer or understeer, it is ultimately the trailer overwhelming the tow vehicle front axle traction initially, then into an unrecoverable posture.

It's why when a WD hitch is setup wrong, that the vehicles steering feels floaty. Propensity to sway. Etc.

Hence the need for a weight distribution hitch. To return front axle weight, traction, directional influence, and stability for control.

Which is very relevant to this thread. The OP may not appreciate that a level tow vehicle is not the same as one setup with weight distribution for proper stability. Hopefully this thread will do that so they don't find out the hard way.

[Collyn]

Originally Posted by gator.bigfoot

I'll believe the guy who sets up hundreds of trailers every year and has setup just about any vehicle and trailer out there. The guy who tests the combination for stability and handling and a bunch of "armchair engineers". Seems to me these armchair engineers just want to get recognized for knowledge they don't have. Book knowledge and experience are 2 different things in my world. I meet people like you every day and in my mind they should have found a different career.

I am intrigued by how you believe it is feasible to for a non-engineer to 'test for' stability and handling without a very real risk of writing off the rig.

I am an engineer and have done such testing many times (by using outriggers) and on a dedicated motor industry proving ground (MIRA in the UK).

Collyn

[AlbertF]

Originally Posted by Collyn

I am intrigued by how you believe it is feasible to for a non-engineer to 'test for' stability and handling without a very real risk of writing off the rig.



I am an engineer and have done such testing many times (by using outriggers) and on a dedicated motor industry proving ground (MIRA in the UK).



Collyn

Have you watched the videos on his website?

[Shiny16]

Originally Posted by gator.bigfoot

I'll believe the guy who sets up hundreds of trailers every year and has setup just about any vehicle and trailer out there. The guy who tests the combination for stability and handling and a bunch of "armchair engineers". Seems to me these armchair engineers just want to get recognized for knowledge they don't have. Book knowledge and experience are 2 different things in my world. I meet people like you every day and in my mind they should have found a different career.

Yep. That Isaac Newton guy is just clueless.

[Collyn]

Originally Posted by AlbertF

Have you watched the videos on his website?

I do show a fair bit of testing gear etc (and major articles re towing etc) on my website - but forum rules (that I totally accept) preclude my personally naming it.

Collyn

[Shiny16]

When you buy a new vehicle it comes with placards that set limits for the vehicle. I’m sure this is in no small part involves a great deal of input from trained engineers. I’m curious. When CanAm does a modification and sets up a vehicle to tow more then the restrictions put in place by the manufacturer do they offer any paperwork or signed endorsement attesting to the new weight?

[Shiny16]

Originally Posted by gator.bigfoot

I'll believe the guy who sets up hundreds of trailers every year and has setup just about any vehicle and trailer out there. The guy who tests the combination for stability and handling and a bunch of "armchair engineers". Seems to me these armchair engineers just want to get recognized for knowledge they don't have. Book knowledge and experience are 2 different things in my world. I meet people like you every day and in my mind they should have found a different career.

I operate the machine that is a requirement of my job within the specs and limits set by the engineers that designed it. The kind of engineers that have degrees. The book learning kind. If I wanted to be an engineer I would have gotten an engineering degree.

[AlbertF]

Originally Posted by Shiny16

When you buy a new vehicle it comes with placards that set limits for the vehicle. I’m sure this is in no small part involves a great deal of input from trained engineers. I’m curious. When CanAm does a modification and sets up a vehicle to tow more then the restrictions put in place by the manufacturer do they offer any paperwork or signed endorsement attesting to the new weight?

No, they do not. But they don’t modify vehicles either. They install receivers - either their own design or reinforced third party products - and wiring and electric brake controllers. They may recommend better tires, and sometimes recommend better shock absorbers. Any competent RV dealer would do these things. I would not consider any of these items to be “modifications.”

There is one thing that Can Am doesn’t typically do, which is adding air bags to “help” the rear springs of a tow vehicle. They utilize properly adjusted weight distributing hitches instead.

They’ve set up two Volvos for me. After 50 000 km (about 31,000 miles) of towing, I have no reason to doubt the reasonableness of what they’re doing.

This is an interesting thread, and I’m trying to maintain an open mind, but the threat of oversteer at the limits of adhesion isn’t causing me to lose any sleep.

Maybe it’s because I grew up in a snowbelt region and I consider the ability to drift a car an important element of being a truly safe driver.

[Collyn]

Originally Posted by AlbertF

No, they do not. But they don’t modify vehicles either. They install receivers - either their own design or reinforced third party products - and wiring and electric brake controllers. They may recommend better tires, and sometimes recommend better shock absorbers. Any competent RV dealer would do these things. I would not consider any of these items to be “modifications.”

There is one thing that Can Am doesn’t typically do, which is adding air bags to “help” the rear springs of a tow vehicle. They utilize properly adjusted weight distributing hitches instead.

They’ve set up two Volvos for me. After 50 000 km (about 31,000 miles) of towing, I have no reason to doubt the reasonableness of what they’re doing.

This is an interesting thread, and I’m trying to maintain an open mind, but the threat of oversteer at the limits of adhesion isn’t causing me to lose any sleep.

Maybe it’s because I grew up in a snowbelt region and I consider the ability to drift a car an important element of being a truly safe driver.

I agree totally re your last para - my wife grew up in Finland and has no issues if her car drifts at speed. It is, however, close to impossible to correct a tow vehicle and trailer by steering if it starts snaking above its critical speed. This is because all ongoing movements are random-like. The best the driver can do is to hold the steering wheel firmly and centrally.

Re the ongoing sneers at engineers - do they seriously feel a Boeing 747 is designed by mechanics?

Collyn

[gator.bigfoot]

Originally Posted by Collyn

I am intrigued by how you believe it is feasible to for a non-engineer to 'test for' stability and handling without a very real risk of writing off the rig.

I am an engineer and have done such testing many times (by using outriggers) and on a dedicated motor industry proving ground (MIRA in the UK).

Collyn

You don't need time be an engineer to test things. You just need common sense, which doesn't exist much. I work in the auto industry. Over here in sunny UK as I type, working on the latest electric vehicles. I see what goes on. I work with dozens of engineers every day. I wish most of them would go back to school and learn some more. I'd rather work with guys who don't have an engineering degree but are skilled in what they do and can think on their feet than a bunch of theoretical engineers that have not actually had practical experience. Those things are world's apart. Practice and theory, I'll take the guy with the practice any day. Don't get me wrong, some engineering is needed. But an engineer with experience. I usually find it is the guy without the degree that teaches the guy with one about the real world.

[BayouBiker]

Originally Posted by AlbertF

Have you watched the videos on his website?

Yes, possibly all of them, the test conditions used, demonstrate handling performance and driving skills generally well within the combination safe operating limits. Certainly within the conditions the system is able to manage oversteer. The videos do not test response to static instability (positive feedback oversteer) or dynamic instability (amplifying sway) both of which lead to a jackknife and probable rollover if not arrested early in the event. Since there are no tests for these issue, the owner cannot possibly know the range of safe conditions.

[Andrew T]

The assumption that a trailer will inevitably sway if the speed is high enough is funny. This combination I have had over 100 mph. Don’t try that with your HD truck. Oh yea you can’t it’s governed at 90 to protect you from the instability.

When I am asked if I am an engineer. My reply is “no I’m just the poor schmuck who has spent his life fixing things an engineer said would work”.

That’s my joke anyway. In truth though I have a lot of respect for what good engineering can do. There is a lot of truly bad engineering though. Of course a huge amount of engineering time is spent on reducing weight and cost. We don’t believe the trailer hitch is the place to do that.

Most modern cars and unit body SUV’s are amazing tow vehicles compared to what was available 50 years ago. However 50 years ago most testing was done with correctly configured hitch systems. Today they test with terrible hitch systems so current automotive engineers have never actually tested a great hitch with a great tow vehicle even if the higher ups would let them.

However even if they wanted to the engineer usually has their hands tied by marketing, bean counters and don’t forget legal. Outside looking in though I think marketing must win as there are some truly terrible tow vehicles with way too high a tow rating that I’m sure some engineer held his nose and looked the other way.

Interesting, the first Front Drive V6 rack and pinion steering, 4 wheel independent suspension Oldsmobile 88 we put a hitch on was for a GM engineer so he could tow his 31’ Airstream. It worked so well we got one of our own. When customers test towed with it they were blown away and we put hitches on 400 of them over the years.