Reply
 
Thread Tools Search this Thread Display Modes
 
Old 07-04-2015, 10:39 AM   #1
Rivet Master
 
John&Vicki's Avatar
 
1990 25' Excella
Sisters , Oregon
Join Date: Jul 2013
Posts: 887
Images: 4
Oversteer - Tail Wagging the Dog

When you see the tree you're going to hit, that's called understeer. If you can only hear and feel it, it's oversteer.

There's another active thread right now that discusses the dangers of towing on sharp declines. If speed isn't controlled carefully, especially when entering a curve at the end of a decline, the trailer can take over with disasterous results, such as a roll-over. It appears to me to be very similar to oversteer, something I'm familiar with.

Early Porsches, with the engine in the rear, are notorious for oversteer. Ralph Nader pretty much got the "unsafe at any speed" rear engined Corvairs off the road. Porsches, while having much better handling, are every bit as bad.

When you drive an early Porsche at high speeds, such as on the track, you learn to scrub speed before entering a curve: slow in, fast out. Hitting the brakes, or even lifting on the throttle, too late in the middle of a curve is a strict no-no and can result in your car going by you. An exception is that experienced Porsche drivers use oversteer to their advantage by throttle steering through curves: go in hot, lift a bit in the middle which kicks out the rear end, then re-apply the throttle when you're pointed the direction you want to go.

So who cares - this is an Airstream forum.

I haven't seen oversteer discussed here, but I think we potentially have a big case of it when towing a trailer. Unlike a Porsche engine which weighs a few hundred pounds, we have thousands of pounds of inert weight back there. I suspect that oversteer may be a factor in many accidents involving down grades and curves. I know trailers have brakes which helps a lot but consider the following scenario:

A driver has been on a long downgrade and has used his brakes a lot to control his speed as opposed to downshifting. Trailer drum brakes are primitive and are probably hot and fading at this point, while the more sophisticated car brakes are still working fine. He enters a curve too fast and hits his brakes - the car slows down and the trailer keeps going. Now the tail is wagging the dog.

On downgrades I think the key to prevent this is to go slow and control the speed with the engine as much as possible by down-shifting. And on twisty roads the key is slow to the correct speed before entering the curve, not midway through.

Cheers,
John
__________________

__________________
John & Vicki
WBCCI #4291

Grown men don't need leaders. ~ Edward Abbey
John&Vicki is offline   Reply With Quote
Old 07-04-2015, 11:39 AM   #2
Rivet Master
 
Alphonse's Avatar

 
2010 28' Flying Cloud
Lower Alabama , USA
Join Date: Mar 2012
Posts: 649
John, great point. You are correct that we don't see much discussion about it. There are a couple of folks here who I have seen speak up about it and give some good advice.

As you point out, slow and easy down the hill or this oversteer stuff can come violently into play when the trailer tries to pass you. We often forget that the kinetic energy of it all is proportional to the square of the speed. Too fast equates to a system with big energy in it to take you down.
__________________

__________________
Alan
"If you must choose between two evils, pick the one you never tried before!"

Air #64439
Southeastern Camping Unit WBCCI #5033
TAC AL-8
2017 Canopenian
Alphonse is offline   Reply With Quote
Old 07-04-2015, 12:31 PM   #3
Rivet Master
 
John&Vicki's Avatar
 
1990 25' Excella
Sisters , Oregon
Join Date: Jul 2013
Posts: 887
Images: 4
A crollary to this is countering trailer sway. Again, when the trailer starts swaying the reaction is to lift on the accelerator and step on the brakes. That just encorages that beast in the back to try and pass you. Just as with a Porsche in a curve you shouldn't brake and you shouldn't lift on the throttle. Just gently maintain speed and use the brake controller manually to slow the trailer and restore the tension between it and the tow vehicle. So much of this is counter intuitive. I'm really grateful that I've had so much seat time in a vehicle that grossly oversteers. Kind of like practice for towing a trailer.

Cheers,
John
__________________
John & Vicki
WBCCI #4291

Grown men don't need leaders. ~ Edward Abbey
John&Vicki is offline   Reply With Quote
Old 07-05-2015, 01:48 AM   #4
4 Rivet Member
 
2007 27' International CCD FB
San Diego , California
Join Date: Sep 2014
Posts: 328
Thank you for starting this thread. It's definitely a topic that is not well understood and worth more discussion on.

I like the Porsche analogy as it resonates with me but perhaps may not with others. The key here is that the rear engine Porsche's carry a high percentage of weight at the rear, and under trail braking conditions in a turn, the rear has a propensity to pass the front end.

This dynamic is even more serious in a articulated vehicle.

Specifically, this is the condition where the tow vehicle is contributing the majority of braking (i.e. engine braking, badly setup trailer brake bias, bad trailer brakes). In this state, stability will be compromised in a turn or evasive maneuver.

Once an angle is introduced to the coupling, the momentum of the trailer will be translated into yaw on the tow vehicle. This induced yaw, will add additional angle onto the coupling, which adds additional yaw leverage on the tow vehicle. A situation that can quickly spiral out of control if not recognized by the driver.

Like the Porsche example, braking may exacerbate the situation. I say may because that depends on all the equipment working and the brake bias in the brake controller to be configured correctly.

The safer response is to apply manual trailer brakes via the brake controller or even accelerate.
__________________
pteck is offline   Reply With Quote
Old 07-05-2015, 02:40 AM   #5
Rivet Master
 
2016 30' International
Scottsdale , Arizona
Join Date: Jul 2010
Posts: 723
Great topic!

A related side note... as a motorcycle rider, one learns quickly that the time to scrub speed is prior to entering the curve and then to accelerate through it. If you find yourself too fast and you're in the curve... MUCH better to just hold steady on the throttle and lean into the curve even harder, than to grab the brakes and throw all the dynamics into a tizzy. And then, don't make that mistake ever again! Motorcycle curve techniques and dynamics are very much like driving a 911 (which I drove for a few years in the mid 1970's).

In addition, well developed skills in situational awareness is something that serves the motorcyclist VERY well, and it applies well to driving all manner of much larger vehicles, as well. Not that I would advise EVERYONE learn to ride a motorcycle, but it imparts valuable learning which I have found applicable to other vehicles including driving a 44' Class A motor coach, pulling a 5th wheel, and a trailer.
__________________
DHart is offline   Reply With Quote
Old 07-05-2015, 10:04 AM   #6
Rivet Master
 
Silver Otter's Avatar

 
2011 31' Classic
Nellysford , Virginia
Join Date: Mar 2011
Posts: 979
Images: 6
Blog Entries: 1
Quote:
Originally Posted by DHart View Post
Great topic!

A related side note... as a motorcycle rider, one learns quickly that the time to scrub speed is prior to entering the curve and then to accelerate through it. If you find yourself too fast and you're in the curve... MUCH better to just hold steady on the throttle and lean into the curve even harder, than to grab the brakes and throw all the dynamics into a tizzy. And then, don't make that mistake ever again! Motorcycle curve techniques and dynamics are very much like driving a 911 (which I drove for a few years in the mid 1970's).

In addition, well developed skills in situational awareness is something that serves the motorcyclist VERY well, and it applies well to driving all manner of much larger vehicles, as well. Not that I would advise EVERYONE learn to ride a motorcycle, but it imparts valuable learning which I have found applicable to other vehicles including driving a 44' Class A motor coach, pulling a 5th wheel, and a trailer.

Great comment, Dhart. As an old Motorcycle Safety Foundation Instructor, I feel I'm a better truck/trailer driver for my training in Bike handling as described above.
__________________
Greg and Linda Heuer
2011 31' Classic Ltd. - The Silver Otter III
2013 GMC Denali 2500HD 6.6 DuraMax
TAC VA-18 | WBAC 1927 - Shen. Valley Unit 149 | AIR 53869
https://www.linkedin.com/in/gheuer
Silver Otter is offline   Reply With Quote
Old 07-05-2015, 10:22 AM   #7
Rivet Master
 
Wingeezer's Avatar
 
2005 30' Classic
Burlington , Ontario
Join Date: Sep 2008
Posts: 2,709
Quote:
Originally Posted by Silver Otter View Post
Great comment, Dhart. As an old Motorcycle Safety Foundation Instructor, I feel I'm a better truck/trailer driver for my training in Bike handling as described above.
I agree whole heartedly. Apart from being more aware of the physics involved,
I think that the years I have spent on two wheels serve to make me much more of a defensive driver when on 2 wheels or 4, and even more when towing.

You just seem to automatically expect the other guy to screw up and constantly assess what you would do when he/she does, what would be your options and escape route etc.?

It also makes you aware of things such as staying out of other people's blind spots, and not driving too close behind large trucks where your forward visibility is severely limited and you may suddenly be faced with a huge chunk of tire lying in the road in front of you with insufficient time to react.

Brian.
__________________
Brian & Connie Mitchell

2005 Classic 30'
Hensley Arrow / Centramatics
2008 GMC Sierra SLT 2500HD,4x4,Crew Cab, Diesel, Leer cap.
Wingeezer is offline   Reply With Quote
Old 07-05-2015, 11:09 AM   #8
Rivet Master
 
A W Warn's Avatar
 
2000 25' Safari
1999 34' Excella
Davidson County, NC , Highlands County, FL
Join Date: Aug 2006
Posts: 2,571
Quote:
Originally Posted by John&Vicki View Post
go slow and control the speed with the engine as much as possible by down-shifting. And on twisty roads the key is slow to the correct speed before entering the curve, not midway through.

Cheers,
John
Excellent advice!
__________________
Alan
2014 Silverado 1500 Crew Cab 5.3L maximum trailering package (yes, I'm towing the 34')
A W Warn is offline   Reply With Quote
Old 07-05-2015, 12:00 PM   #9
Rivet Master
 
John&Vicki's Avatar
 
1990 25' Excella
Sisters , Oregon
Join Date: Jul 2013
Posts: 887
Images: 4
Thanks for the post pteck. Your technical explanation of oversteer really adds to the discussion and my basic comments. And great input from those experienced with motorcycles. It's not that common to have experience with oversteer as almost all vehicles have engines in the front with a tendency to understeer. I think it's valuable for those of us who have experienced oversteer by happenstance to share our experiences. A good understanding of this topic should help to make us all safer out there, regardless of our trailer, TV and hitch. Physics trumps everything.

Cheers,
John
__________________
John & Vicki
WBCCI #4291

Grown men don't need leaders. ~ Edward Abbey
John&Vicki is offline   Reply With Quote
Old 07-05-2015, 07:25 PM   #10
4 Rivet Member
 
gecko's Avatar
 
2009 28' International
Pacific Palisades , California
Join Date: Dec 2009
Posts: 372
John--great thread! Three comments: (1) in curves, (and especially downhill) ALL vehicles should be driven like Porsches and motorcycles--just makes sense for all the great explanations here (2) it makes sense to set the trailer brakes to be just s bit stronger than the tow vehicles. In the event that you actually do have to brake downhill on a curve (elk, anyone?), this will let the not overtaxed (because you haven't been riding them, of course) trailer brakes to make trailer serve as a sea anchor,slightly holding back the lead vehicle instead of pushing it and (3) with the combo of EARLY engine braking and EARLY vey light straight brake application well before the curve, you can easily control your speed while in the vulnerable downhill mode.
__________________
gecko is offline   Reply With Quote
Old 07-05-2015, 09:30 PM   #11
Rivet Master
 
tjdonahoe's Avatar
 
2013 31' Classic
billings , Montana
Join Date: Feb 2010
Posts: 1,843
Every one is still talking about the Bozeman pass accidents, well it is a cake walk if you pay attention, we been traveling it up and down in our big trucks and with our travel trailers for over thirty years with no problems, with very little service braking,the jake brake and exhaust brake doing most of the work.....
__________________
tjdonahoe is offline   Reply With Quote
Old 07-05-2015, 10:44 PM   #12
Rivet Master
 
Lumatic's Avatar

 
1971 25' Tradewind
1993 34' Excella
Currently Looking...
Estancia , New Mexico
Join Date: Feb 2005
Posts: 6,642
Images: 16
Blog Entries: 1
Trailer Brakes First! https://video.search.yahoo.com/video...sigi=11v52jveh
__________________
Sail on silver girl. Sail on by. Your time has come to shine.
Lumatic is offline   Reply With Quote
Old 07-06-2015, 08:42 AM   #13
Rivet Master
 
m.hony's Avatar
 
2013 30' Classic
Greenwood , Mississippi
Join Date: Oct 2012
Posts: 11,832
Everything we ever wanted to know about towing a trailer (40 feet of train!) we can learn from Lucille Ball and Desi Arnaz, or from Clinton Twiss, the author of the book.
__________________
2013 Classic 30 Limited
2007 Silver Toyota Tundra Crew Max Limited 5.7 iForce
2006 Vivid Black Harley-Davidson Road King Classic
1999 Black Nissan Pathfinder LE
TAC #MS-10
WBCCI #1811, Region 6, Unit 56
Airforums #70955
m.hony is offline   Reply With Quote
Old 07-06-2015, 09:16 AM   #14
Rivet Master
 
switz's Avatar

 
2014 31' Classic
2015 23' International
2013 25' FB International
Apache Junction , Arizona
Join Date: Sep 2012
Posts: 4,799
Images: 8
Those yellow speed caution signs with lower speed numbers than the posted speed limits are there for a reason. I would suggest that when towing, the driver should drop speed to that caution number or even lower when on steep grades.

We have a challenge on every trip when heading North or East by going through Salt River Canyon east of Phoenix. The posted speed limit when transiting the actual canyon is 35 while some turns are cautioned at 25. The grade is steep and the turns are tight with the mountain right at the edge of the road.

On a motorcycle, this is great sport as long as no loose gravel is on the road from a recent rain....

I keep a longer than normal gap between me and the vehicle head and let the engine brake hold the speed at or below posted or the yellow sign speed. I grab the trailer disc brake controller to apply some braking action if the speed starts to creep upwards sort of like releasing a drag chute. That keeps the rig in line.

The longer gap allows me to watch all the brake lights light up on the vehicles ahead and just let up on the throttle to keep the distance. Whenever this is a small pull off, I let the speed demons pass as they like to be about 10 feet off the trailer bumper.
__________________

__________________
WBCCI Life Member 5123, AIR 70341, 4CU, WD9EMC

TV - 2012 Dodge 2500 4x4 Cummins HO, automatic, Centramatics, Kelderman level ride airbag suspension, bed shell

2014 31' Classic model 30 twin beds, 50 amp service, 900 watt solar system, Centramatics, Dill TPMS, disc brakes, 16" tires & wheels
switz 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
Does the tail wag the dog? MrUKToad Towing, Tow Vehicles & Hitches 56 08-14-2013 07:21 AM
Leak near tail light, but it's not the tail light adwriter73 Leaks - Weatherstrips, Gaskets, Caulks & Sealants 7 03-31-2013 12:34 PM
First dog in AS - how do you eliminate that dog smell? Whirlaway The Pet Forum 42 03-22-2010 06:54 PM
A/S Dog Rescue - happy ending Creampuff The Pet Forum 6 02-23-2004 01:49 PM
Our Second Outing, Dog's First....not so good!!! 71Overlander The Pet Forum 43 09-22-2003 08:53 PM


Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 11:24 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.