Tire Stiffness & trailer swaying

(JJ Sinclair) wrote in message
There was a lot said on the *Komet Trailer Fin* causing instability, about a
year ago. I typed in *Komet Trailer* into Google and found a good report by,
Dan Dunkel. He was able to tame the beast by adding turbulators on each side of
his trailer fin. This report is on page 3 of Google, under Komet Trailer.
Hope this helps,

JJ Sinclair

JJ,

Last year I installed the turbulator strip on my Komet fin. It is
about .75" [19mm] high and about 3" [75mm] back from the front of the
fin. [aluminum extrusion]. It has made a very noticeable difference,
and stablilzed the trailer at higher speeds, especially behind the
disturbed flow of 18wheel trucks. This cured an aerodynamic problem
that felt aerodynamic.

I also did a short test drive with the rear hatch of the Forester
open. This should have significantly altered the airflow between the
tow vehicle and the trailer. This had no impact on the swaying issue.
The swaying issue begins with a steering input, does not appear/feel
to be aerodynamic in nature. [And even if it were the Forester does
not seem to have much steering response on these tires to counteract
the motion].

Also the swaying starts at about 45mph [72km/h] which is low for this
much force to be generated aerodynamically.

Thanks for the feedback,
Chris

Chris wrote
Also the swaying starts at about 45mph

Have you tried adding shock absorbers? Don't jump my sierra, if this has been
covered, I haven't been following along. I had a utility trailer that would
sway so much I was afraid it would dump its load, adding shocks did the trick.


JJ Sinclair

"chris" wrote in message
om...
(JJ Sinclair) wrote in message
There was a lot said on the *Komet Trailer Fin* causing instability,
about a
year ago. I typed in *Komet Trailer* into Google and found a good report
by,
Dan Dunkel. He was able to tame the beast by adding turbulators on each
side of
his trailer fin. This report is on page 3 of Google, under Komet
Trailer.
Hope this helps,

JJ Sinclair

JJ,

Last year I installed the turbulator strip on my Komet fin. It is
about .75" [19mm] high and about 3" [75mm] back from the front of the
fin. [aluminum extrusion]. It has made a very noticeable difference,
and stablilzed the trailer at higher speeds, especially behind the
disturbed flow of 18wheel trucks. This cured an aerodynamic problem
that felt aerodynamic.

I also did a short test drive with the rear hatch of the Forester
open. This should have significantly altered the airflow between the
tow vehicle and the trailer. This had no impact on the swaying issue.
The swaying issue begins with a steering input, does not appear/feel
to be aerodynamic in nature. [And even if it were the Forester does
not seem to have much steering response on these tires to counteract
the motion].

Also the swaying starts at about 45mph [72km/h] which is low for this
much force to be generated aerodynamically.

Thanks for the feedback,
Chris

My Komet trailer has the aluminum spoilers on the fin and it seems to tow
well up to 75MPH - unless there is a sharp steering input like Chris says.
My feeling is that the problem is suspension/tire related. I tow with a
Jeep Grand Cherokee and below 65 MPH the handling is perfect.

I'm pretty sure that the problem is with the Jeep. (Despite remarks to the
contrary, the older Jeep Grand Cherokee (ZJ) is a lightweight among the
current crop of SUV's and not much heavier than the Forester.) I've had
similar but worse problems towing other trailers.

I deliberately started the sway on an empty stretch of interstate highway
and observed that the trailer sways back and forth rotating about the
vertical axis while the Jeep rolls side to side rotating about the
longitudinal axis. In other words the trailer fishtails while the towing
vehicle rolls back and forth. The period of the trailer's sway is the same
as the Jeeps natural roll frequency so there seems to be a destructive
resonance going on. The Jeep rolls in the direction of the travel of the
front of the trailer which suggests that the Jeeps roll center is much lower
than the tow hitch. Lowering the tow ball is not an option for ground
clearance reasons so increasing the Jeep's roll stiffness seems a good way
to go.

So far, I've increased the Jeep's tire pressure up to the point that the
ride is too stiff for comfort and, while it does help, that's not the
solution I want because of the harsh ride. The next try is to replace the
13mm stock rear sway bar with a 25mm diameter ADDCO bar. Since the
handling with the trailer is really quite good below 65 MPH, this is not a
high priority issue with me since slowing down saves a lot of fuel anyway.

Bill Daniels

Definite.
Mondeo and ASW-20
Wonder why you ever had a doubt.

"Tim" escribió en el mensaje
...
Graeme Cant s comments read:

Tim wrote:
Cheers!

I've decided that the combination isn't the best.

So do I trade the 20 for a PW5? Or do I sell the wife and get a Mondeo
????

Post photos of all four and we'll help you decide.

ASW20
http://www.gliderforum.com/photos/sh...9&currentpos=3

PW5
http://www.hotornot.com/r/?eid=N8KRKES&key=WPU

Wife
http://my.tenforward.com/rozebud/button/2/kysmy.jpg

Mondeo
http://www.tiscali.co.uk/motoring/ro...test_14_1.html

So what do you think?
--
Tim - ASW20CL "20"

chris wrote:
...This had no impact on the swaying issue.
The swaying issue begins with a steering input, does not appear/feel
to be aerodynamic in nature. [And even if it were the Forester does
not seem to have much steering response on these tires to counteract
the motion].

Also the swaying starts at about 45mph [72km/h] which is low for this
much force to be generated aerodynamically.

I owned a Forester for a short time a few years ago and I think the
steering is either over-assisted or inadequately self-centreing (or
both!). I suppose you'd say the force gradient is too flat. Whatever
the cause, it always seemed to me to be too sensitive to small inputs.
Unless I rested at least one elbow, the car would readily set up a
slight wander from side to side. It was easy to set up a rhythmical
roll which had very little natural damping even with no trailer
attached. It would drift off line easily with a moment's inattention.

The tyres were probably Bridgestones but I can't be sure now. They
certainly weren't low profile - probably 75-80 (this was the unblown 2
litre - not the GT)

I towed a Blanik about 800kms with the Forester. I certainly didn't
have chris's problems - I drove happily at speeds up to 110km/h with no
trailer instability but I remember it wasn't a relaxing drive and winds
did affect it. I recall carefully keeping my elbows on the armrests to
damp the steering. The drawbar load would have been about 60-70kg and I
followed the book on tyre pressures for max load.

My thought would be that the main problem is the trailer but it's
exacerbated by a car with sensitive steering and inadequate roll
damping. Check the drawbar load and suspension of the trailer first.
It's probably cheaper to move the trailer axle back than to change cars!

I'd agree with the guy who said boost the tyre pressure at the rear but
not the front. Stiffer rear roll bar would be useful. The GT version
probably has lower profile tyres and rims which would help - check if it
has a stiffer roll bar.

The Forester steering is similar to a SAAB I once owned. Audi are a bit
like it too. I think largish FWD cars tend to have dead, over-assisted
steering and Subaru is a 4WD which comes from a FWD tradition. 4WDs
which come from the other end - Land Cruiser, Land Rover - seem to have
better weighted steering and are less sensitive and more stable.

GC

In article . net,
says...
So far, I've increased the Jeep's tire pressure up to the point that the
ride is too stiff for comfort and, while it does help, that's not the
solution I want because of the harsh ride. The next try is to replace the
13mm stock rear sway bar with a 25mm diameter ADDCO bar. Since the
handling with the trailer is really quite good below 65 MPH, this is not a
high priority issue with me since slowing down saves a lot of fuel anyway.

This stiffer bar will tend to move the handling towards oversteer (less
stable in turns) because it increases the load on the outside rear tire
in a turn. Be cautious checking out the handling, and be prepared to
also increase the size of the front sway bar to move the handling
towards understeer (more stable in turns).

--
-------
Eric Greenwell USA

Trailer tires can make a big difference also. In the USA, they are
noted as "ST" (special trailer) rated. My last cobra really swayed
bad until I changed the regular car radials (not cheap ones)on it for
"ST" rated tires.
Since they are made for trailers and thus non-steering, the sidewalls
are stiffer. They did the trick for me. My new cobra has european
radials and it does not do as well, but I've not gotten around to
changing
them. My tow vehicle is a 4WD Tahoe which is no lightweight. High CG
may account for some of the problem also. High quality
tires on the tow vehicle also make a difference.

I can't go along with advocating overinflation of the tires. Up to
the max. allowable yes, but beyond that you become the test driver.

-Deputy Dog


(RHWOODY) wrote in message ...
This may be helpful - over inflate the
rear vehicle tires - at least maximum
pressure - leave the front vehicle tires
at normal pressure (dampening) -
and at least maximum pressure in the
trailer tires - over inflation is better.
This is the most stable configuration.
Additionally, buy a couple 5 gallon
canisters and fill them with water and
place them in the front of the trailer.
Good luck, and drive safe.

Personal choice and the sensible matching of the tow vehicle to the
trailer is what it is all about.

I should explain that here in California where we are recalling our
Governor one of the over 140 candidates is placing tv ads stating that
if you drive an SUV you support terrorism. This candidate now also
supports the governor who made it legal for illegal immigrants to
obtain a drivers license. Go figure. Other people label SUV drivers as
antisocial. Give me a break. You can be just as 'antisocial' on the
road in a Civic as well as in a Tahoe; or flying a Ventus as well as a
PW5. So some of SUV drivers here are just a bit touchy about all that!

Alex Chappell wrote in message ...
As long as it's stable who cares?
I know people who have walked away from pretty scary
accidents - punctures at speed limit whilst towing
on dual carriageway and the like - when it has been
a sensible, well behaved combination, SUV or otherwise.
Equally, there are combinations which are just an
accident waiting to happen. Once it gets out of control,
the soggy suspension and high C of G just make an SUV
dead easy for the trailer to flip, however heavy it
is (ever watched wrestling?)
Light cars are easily steered by big trailers.

Don't know about in the US, but here in the UK you
could probably put all trailer smashes down to one
of three things:

1. lightweight cars with a large distance betweeen
the rear axle and hitch. Plenty of these around here.
The trailer does the steering especially if it is heavy.

2. Rogue trailers. Most trailers are perfectly OK towed
within the limits. Some change dramatically between
empty and loaded. I remember a ? homebuilt two-seater
trailer which loaded was a nightmare and empty was
almost impossible. I know of trailers which use old
caravan suspension components or car tyres, which are
almost always not stiff enough. Get one of these on
an SUV and it would be interesting.


3. Bad driving.Self explanatory.

Have a nice day

Al

At 16:12 29 September 2003, Bruce Greeff wrote:
Hi Graeme

Lots of prejudices here mate, sorry if I offended.

Maybe it is a SIFOW thing, I prefer not driving trucks.

Again each to his own.

In article .net,
says...
Absolutely true Eric. Anyone contemplating such a modification should be
quite careful.

The Jeep GC comes stock with a 1.25" front bar and a .5" rear bar which
results in extreme understeer. The word on the Jeep forums is that the
ADDCO 1" rear bar improves on-road handling a lot while hurting the off-road
capability a bit.

I just recalled that years ago I improved the handling of my '89 Dodge
Grand Caravan by adding a rear sway bar, because it had way too much
understeer. It didn't noticeably affect the stability while trailering,
or hurt the ride except for speed bumps taken diagonally. Let us know
how the bigger bar works out.
--
-------
Eric Greenwell USA

"Eric Greenwell" wrote in message
t...
In article .net,
says...
Absolutely true Eric. Anyone contemplating such a modification should be
quite careful.

The Jeep GC comes stock with a 1.25" front bar and a .5" rear bar which
results in extreme understeer. The word on the Jeep forums is that the
ADDCO 1" rear bar improves on-road handling a lot while hurting the
off-road
capability a bit.

I just recalled that years ago I improved the handling of my '89 Dodge
Grand Caravan by adding a rear sway bar, because it had way too much
understeer. It didn't noticeably affect the stability while trailering,
or hurt the ride except for speed bumps taken diagonally. Let us know
how the bigger bar works out.
--
-------
Eric Greenwell USA

Way back when I was dabbling in sports car racing, there was a saying about
understeer and oversteer. They said that if a Jaguar (understeer) driver
lost control and went off the race course, he would make a hole in the
boundary fence rolling forwards. If a Porsche (oversteer) driver lost
control, he would go through the same hole in the fence the Jag made but
going backwards.

Bill Daniels