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Tire Stiffness & trailer swaying



 
 
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  #1  
Old September 25th 03, 03:13 PM
chris
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Default Tire Stiffness & trailer swaying

Several people have had good luck towing a glider with a Subaru
Forester.
I do not know why mine is different.
I just bought a 2004 Forester tried to tow with it. Mine is a
nightmare. It is unstable above 50mph. It has a lot of side to side
sway above 50mph if there is any steering input. It is almost
harmonic in nature – it does not dampen out quickly. If feels like
you are driving on Jello. It feels like the problem is much more the
tires than the suspension. Though that is hard to prove.

Even when parked if you push on the hitch with your foot the Forester
will sway side to side [right and left] a lot. You can watch the rim
move right and left in and out of the tire. I think the sidewalls are
just really weak. The tread is probably relatively soft also.

The Forester's tires are Yokohama Geolander G900 P215/60 R16 94H.
Even in normal driving the steering response and cornering are poor.
[Other Foresters may be equipped with 15" tires, and other models of
Geolander tires – rather than the G900].

My Mazda MX-6 [much lower car] has Pirelli P4000 P205/55 R15 87H – it
is stable, and if you push sideways it does not sway side to side
anywhere near the degree that the Forester does. Steering response
and cornering are good.

The Geolander G900 has a tall soft sidewall, it is 4.500" above the
rim rather than 3.625" for the P4000 [24%higher].

My best idea right now is to change to a shorter and stiffer sidewall
tire.
I am considering changing from P215/60 R16 94H
- an "H" rate tire with 60% width/height ratio, to
Bridgestone Turanza LS-V 225/50R16 92V - this is a V rate tire so the
sidewall is stiffer and at a 50 or 55 ratio it is shorter.
This is the V rated version of the tire that some other Forester
owners have [LS-H]. The tread should also be a harder sports car like
compound.



Some of these tires are rated and discussed on www.tirerack.com. It
seems that Steering response and cornering stability are good
expressions of my issue.
On tirerack there are a mass of good comments on the Turanza tire –
though I doubt anyone is towing. As far as I can tell everyone on
"tirerack" hates the geolander 900 like on mine.


Does anyone else have any Experience changing to a shorter V rated
tire for better stability?


My trailer does great and stable to 85+mph behind my Mazda MX-6, so I
do not think it is the trailer. The trailer is a 1979 Komet with a
Mosquito. It weighs ~1800lbs [816kg]. The tongue weight is 153lbs
[69kg]. The Forester's manual says to keep the tongue weight between
8-11% of the trailer. 8%=144lbs [65kg] 11%=198lbs [90kg].
[the max allowed is 200lbs on the tongue] The manual transmission
version of the Forester is rated for 2400lbs [1088kg] towing capacity.


I have already tried raising the tire pressure on the rear tires to
41psi [2.8bar] as recommended by the manual. The trailer tires are
about 40psi.


Chris Ruf

  #2  
Old September 25th 03, 04:10 PM
Bill Daniels
external usenet poster
 
Posts: n/a
Default


"chris" wrote in message
om...
Several people have had good luck towing a glider with a Subaru
Forester.
I do not know why mine is different.
I just bought a 2004 Forester tried to tow with it. Mine is a
nightmare. It is unstable above 50mph. It has a lot of side to side
sway above 50mph if there is any steering input. It is almost
harmonic in nature - it does not dampen out quickly. If feels like
you are driving on Jello. It feels like the problem is much more the
tires than the suspension. Though that is hard to prove.

Even when parked if you push on the hitch with your foot the Forester
will sway side to side [right and left] a lot. You can watch the rim
move right and left in and out of the tire. I think the sidewalls are
just really weak. The tread is probably relatively soft also.

The Forester's tires are Yokohama Geolander G900 P215/60 R16 94H.
Even in normal driving the steering response and cornering are poor.
[Other Foresters may be equipped with 15" tires, and other models of
Geolander tires - rather than the G900].

My Mazda MX-6 [much lower car] has Pirelli P4000 P205/55 R15 87H - it
is stable, and if you push sideways it does not sway side to side
anywhere near the degree that the Forester does. Steering response
and cornering are good.

The Geolander G900 has a tall soft sidewall, it is 4.500" above the
rim rather than 3.625" for the P4000 [24%higher].

My best idea right now is to change to a shorter and stiffer sidewall
tire.
I am considering changing from P215/60 R16 94H
- an "H" rate tire with 60% width/height ratio, to
Bridgestone Turanza LS-V 225/50R16 92V - this is a V rate tire so the
sidewall is stiffer and at a 50 or 55 ratio it is shorter.
This is the V rated version of the tire that some other Forester
owners have [LS-H]. The tread should also be a harder sports car like
compound.



Some of these tires are rated and discussed on www.tirerack.com. It
seems that Steering response and cornering stability are good
expressions of my issue.
On tirerack there are a mass of good comments on the Turanza tire -
though I doubt anyone is towing. As far as I can tell everyone on
"tirerack" hates the geolander 900 like on mine.


Does anyone else have any Experience changing to a shorter V rated
tire for better stability?


My trailer does great and stable to 85+mph behind my Mazda MX-6, so I
do not think it is the trailer. The trailer is a 1979 Komet with a
Mosquito. It weighs ~1800lbs [816kg]. The tongue weight is 153lbs
[69kg]. The Forester's manual says to keep the tongue weight between
8-11% of the trailer. 8%=144lbs [65kg] 11%=198lbs [90kg].
[the max allowed is 200lbs on the tongue] The manual transmission
version of the Forester is rated for 2400lbs [1088kg] towing capacity.


I have already tried raising the tire pressure on the rear tires to
41psi [2.8bar] as recommended by the manual. The trailer tires are
about 40psi.


Chris Ruf


You're right that tow vehicles often get overlooked when trailer sway is an
issue.

You can increase the stiffness of a tire a lot by just increasing the air
pressure. Try adding another 10PSI to the normal inflation pressure and see
what happens. If that helps, sidewall stiffness is likely to be the
problem - if not, the problem may be elsewhere.

There is another issue with SUV's suspensions that are intended for real
offroad operation. Often roll stiffness is greatly reduced compared to
normal passenger vehicles to minimize the neck-snapping side-to-side motion
on rough trails. This softer roll compliance combined with a higher CG also
means that trailer sway will induce a side-to-side rolling motion in the SUV
that, in turn, augments the trailer sway in a nasty feedback loop.

The fix is to replace the wimpy rear sway bar with a stiffer aftermarket one
from a company like Addco. Depending on the vehicle, you may also want to
replace the soft rubber sway bar bushings with a harder material like
urethane. The penalty for this modification is that the ride will be less
comfortable on rough surfaces.

Bill Daniels

  #3  
Old September 25th 03, 07:33 PM
Scott Correa
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Posts: n/a
Default


"chris" wrote in message
om...
The Forester's tires are Yokohama Geolander G900 P215/60 R16 94H.
Even in normal driving the steering response and cornering are poor.
[Other Foresters may be equipped with 15" tires, and other models of
Geolander tires - rather than the G900].


Chris.
My Tahoe on Geolanders (nice tire) handles very poorly at less than
44 psi all 4 corners. This is a truck rated tire and very succeptable to
underfilled type of problems. The symptoms sound like low tire pressure.
First, have a tire shop check the pressures. THEN use your gauge to make
sure
it is in the ballpark. I've seen cheapo gauges read way off after being
dropped,
not to mention not being very close to begin with.

Does your hitch have sufficient drop. If you are using the same
reciever/ball
you probably need to change top a lower dropped unit. If the ball is too
high
and the trailer is appreciably "nose up" they seem to want to oscillate
back and forth
without much provocation.

Just thiinking out loud................

Scott Correa


  #4  
Old September 26th 03, 04:04 AM
Chris Ruf
external usenet poster
 
Posts: n/a
Default


Since my original write up I have learned the following:
The dealer told me that the 2004 model is the first to be equipped with the
Geolander G900 tires, previous years had a different model tire. This is
the only change to the suspension that he is aware of between the 2003 and
2004 model.

The Maximum tire pressure on the tires is 44psi, so I upped the rear
pressure to 44psi and the fronts to 41. [for towing the manual says 29psi
front, 41psi rear]. I also changed the hitch from a straight one to a "drop
hitch" it is now 1.5" lower than the straight one. The drop hitch is about
4.0" shorter than the "lift hitch" [bent receiver hitch] that I originally
tried. The hitch ball is on a short receiver.
A test drive showed that the lower hitch/ball placement and the higher tire
pressures are an improvement. However still not acceptable. I think the
higher pressure stiffened the tires but not enough and the tread is still
too soft.

I have heard another Forester owner has had good luck with 75-100lbs of
tongue weight. An additional test drive was done after I moved several items
out of the front of the trailer to the back of the Forester. This reduced
the tongue weight to 118lbs [down 35lbs from 153]. The swaying seemed worse
with the lower tongue weight. [This follows the logic I have heard many
times].

Chris Ruf



  #5  
Old September 26th 03, 06:41 AM
CH
external usenet poster
 
Posts: n/a
Default

I don't know how long it does take for certain people
to recognise, that SUV's and 4-wheel drive cars

- are built for use in the outback and not for driving in towns
- have a high CG and are handling worse on windy roads than
any normal cars with good suspension (European/Japan cars)
- have big tires to suit off road driving, which are worse on
normal roads, worse than normal or low profile tires.
- often do not have independent side stable suspension on the
back which give them bad side stability (push the car sideways
on the rear bumper and let it go - if the hole car swings around
the vertical yaw axis then it does not suit towing)
- have bad aerodynamics and produce more turbulence behind,
which has again bad influence on the trailers stability.

Conclusions:
Quite any car is better for towing, in handling and safety than
a SUV.

I prefer to rent a 4-wheel drive for holiday in the outback,
own a small car with common rail turbo diesel engine
(2000 ccm, 110kW, 250Nm at 1750 rpm, and 4.5 to 6 liters
per 100km consumption).
Like that I can pay many tows with the saved money I do not
spend on petrol.
I can tow any trailer with brakes up to 1500kg stable with
100km/.
And on a windy road the SUV just disappear in the rear mirror.
But I cannot compete offroad with these monsters. I don't mind
because I only need offroad function perhaps 7 days a year.
How often do you need offroad capability?
Think of it when you buy the next car.
Chris


"chris" wrote in message
om...
Several people have had good luck towing a glider with a Subaru
Forester.


My Mazda MX-6 [much lower car] has Pirelli P4000 P205/55 R15 87H - it
is stable, and if you push sideways it does not sway side to side
anywhere near the degree that the Forester does. Steering response
and cornering are good.


Chris Ruf



  #6  
Old September 26th 03, 07:13 AM
tango4
external usenet poster
 
Posts: n/a
Default

Heresy! Devil out, be gone.

You are preaching to the 'hit it with a bigger sledgehammer' mob here lad.
If it aint got 5 litres of V8 petrol engine and 200kgs of tongue weight it
aint right!

:-)

Ian - 2300cc ( petrol I will admit ) Ford MPV and about 53 kgs tongue weight
a proven 100mph combination!


"CH" wrote in message
...
I don't know how long it does take for certain people
to recognise, that SUV's and 4-wheel drive cars

- are built for use in the outback and not for driving in towns
- have a high CG and are handling worse on windy roads than
any normal cars with good suspension (European/Japan cars)
- have big tires to suit off road driving, which are worse on
normal roads, worse than normal or low profile tires.
- often do not have independent side stable suspension on the
back which give them bad side stability (push the car sideways
on the rear bumper and let it go - if the hole car swings around
the vertical yaw axis then it does not suit towing)
- have bad aerodynamics and produce more turbulence behind,
which has again bad influence on the trailers stability.

Conclusions:
Quite any car is better for towing, in handling and safety than
a SUV.

I prefer to rent a 4-wheel drive for holiday in the outback,
own a small car with common rail turbo diesel engine
(2000 ccm, 110kW, 250Nm at 1750 rpm, and 4.5 to 6 liters
per 100km consumption).
Like that I can pay many tows with the saved money I do not
spend on petrol.
I can tow any trailer with brakes up to 1500kg stable with
100km/.
And on a windy road the SUV just disappear in the rear mirror.
But I cannot compete offroad with these monsters. I don't mind
because I only need offroad function perhaps 7 days a year.
How often do you need offroad capability?
Think of it when you buy the next car.
Chris


"chris" wrote in message
om...
Several people have had good luck towing a glider with a Subaru
Forester.


My Mazda MX-6 [much lower car] has Pirelli P4000 P205/55 R15 87H - it
is stable, and if you push sideways it does not sway side to side
anywhere near the degree that the Forester does. Steering response
and cornering are good.


Chris Ruf





  #7  
Old September 26th 03, 10:32 AM
Doug Hoffman
external usenet poster
 
Posts: n/a
Default

Not all SUVs are created equal (I won't get into all-wheel-drive cars,
many of which are *not* designed for offroad use). My Jeep Liberty is
nicely sized for my purposes. I had a landout last year in a freshly
plowed field. Nothing but a very off-road-capable 4WD vehicle could
have performed the retrieve. I was sure glad I had the Jeep! Then
there are the cars I've pulled out of ditches with it during the
winter.

But you are right about the issues with high CG, off-road tires, etc.
Anyone who drives such an SUV like a sports car is a fool.

-Doug


"CH" wrote in message ...
I don't know how long it does take for certain people
to recognise, that SUV's and 4-wheel drive cars

- are built for use in the outback and not for driving in towns
- have a high CG and are handling worse on windy roads than
any normal cars with good suspension (European/Japan cars)
- have big tires to suit off road driving, which are worse on
normal roads, worse than normal or low profile tires.
- often do not have independent side stable suspension on the
back which give them bad side stability (push the car sideways
on the rear bumper and let it go - if the hole car swings around
the vertical yaw axis then it does not suit towing)
- have bad aerodynamics and produce more turbulence behind,
which has again bad influence on the trailers stability.

Conclusions:
Quite any car is better for towing, in handling and safety than
a SUV.

I prefer to rent a 4-wheel drive for holiday in the outback,
own a small car with common rail turbo diesel engine
(2000 ccm, 110kW, 250Nm at 1750 rpm, and 4.5 to 6 liters
per 100km consumption).
Like that I can pay many tows with the saved money I do not
spend on petrol.
I can tow any trailer with brakes up to 1500kg stable with
100km/.
And on a windy road the SUV just disappear in the rear mirror.
But I cannot compete offroad with these monsters. I don't mind
because I only need offroad function perhaps 7 days a year.
How often do you need offroad capability?
Think of it when you buy the next car.
Chris

  #8  
Old September 26th 03, 01:57 PM
Bill Daniels
external usenet poster
 
Posts: n/a
Default


"GeorgeB" wrote in message
...
On Fri, 26 Sep 2003 03:04:36 GMT, "Chris Ruf"
wrote:

The Maximum tire pressure on the tires is 44psi, so I upped the rear
pressure to 44psi and the fronts to 41. [for towing the manual says

29psi
front, 41psi rear].


Generally, you don't want to harden up the fronts ... the sideways
force from the hitch doesn't generate much torque to bother them.
Hard fronts, even not pulling a trailer, often cause high steering
sensitivity. Tongue weight lightens the load on them. That is one of
the reasons for a weight-distributing hitch.


Be careful here to understand the four wheel drive system in your vehicle.
(I think the Subaru uses a central differential and not a viscous coupling
for its full-time 4WD.) However, any full-time 4WD vehicle will suffer very
expensive damage to the transfer case if the front and rear axles turn at
different speeds for an extended time as they would with different tire
pressures.

My Jeep uses and central viscous coupling instead of a center differential
so all four tires must always be the same diameter else very expensive
repairs are in the offing.

Bill Daniels

  #9  
Old September 26th 03, 02:20 PM
Tim
external usenet poster
 
Posts: n/a
Default

"tango4" s comments read:

Ian - 2300cc ( petrol I will admit ) Ford MPV and about 53 kgs tongue weight
a proven 100mph combination!


Ian a proven TINSFOS man

Tim - Peugeot 106 1100cc
A legal 60mph combination

--
Tim - ASW20CL "20"
  #10  
Old September 26th 03, 11:06 PM
ADP
external usenet poster
 
Posts: n/a
Default

I guess the "Ariana Wussies" have hit this forum - even if they aren't from
the US
Give me a break, there are so-called SUVs that can blow the doors off of
anything less than a
new Ferrari and out corner anything built in Japan.
In fact, I'll take my two wheel drive pickup truck and challenge you in
whatever 1000 cc turkey you drive
and race you an any road, any track, anywhere and drub you soundly - and
I'll drub you in a straightaway towing a 2000# load.
And, yes folks, I really can do it!

If you want to push this BS, go to Green Peace. Drive what you want where
and when you want.

The other responses to this thread were on point, what will make his vehicle
handle better while towing.
Please get with it.

Let the games begin!

ADP


"CH" wrote in message
...
I don't know how long it does take for certain people
to recognise, that SUV's and 4-wheel drive cars

- are built for use in the outback and not for driving in towns
- have a high CG and are handling worse on windy roads than
any normal cars with good suspension (European/Japan cars)
- have big tires to suit off road driving, which are worse on
normal roads, worse than normal or low profile tires.
- often do not have independent side stable suspension on the
back which give them bad side stability (push the car sideways
on the rear bumper and let it go - if the hole car swings around
the vertical yaw axis then it does not suit towing)
- have bad aerodynamics and produce more turbulence behind,
which has again bad influence on the trailers stability.

Conclusions:
Quite any car is better for towing, in handling and safety than
a SUV.




 




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