Tires again (but this time on the tow vehicle)

I recently replaced the Original Equipment Michelin MXV4 H-rated tires on my
VW Passat 4 motion wagon (Variant for those of you in Europe) with Dunlop SP
40 A/S all weather radials. Other than lacking a speed rating, they are the
same dimensions as the originals. Although the new tires are okay in
regular driving, I've noticed that the towing performance is much worse.
The car and trailer combination (LS8 in a new Anschau Komet Euro Trailer)
used to be rock solid up to 75mph; any mild trailer wag would damp out
immediately. Now, trailer wag can set up at around 65mph, and it seems
less likely to damp out.

I'm assuming that one aspect of speed rated tires must be a stiffer sidewall
to handle cornering loads. I'm guessing that this may be a part of the
problem. Anyone else experience similar?

Erik Mann (P3)

Hi Erik,

From my experience I think you are right on! Trailer tires are usually
a bias belted tire which have a much stiffer side wall. A previous
thread cited great improvement by using a 17 inch wheel with low
profile (aspect ratio) tires. One way to improve the situation you
describe is to signifigantly increase your rear tire pressure (36-38
psi) and also the pressure of the trailer tires (40 psi). To get a
better feel for the situation, try pushing the rear of your vehicle
sideways with a pulsing effort. When your frequency is close to the
natural frequency in that mode you will be surprised at how little
effort it takes to sustain the motion. If you watch the sidewall while
doing this you will notice that the majority, if not all, of the motion
is in the side wall. The increased pressures will increase the natural
frequency and thereby allow a higher speed before the swaying becomes
objectionable.

Lorry charchian

I tow a large trailer which carries both my Salto sailplane
and my Skybolt biplane behind a Dodge Ram 2500. When
I changed tires a couple of years ago, they inadvertently
installed 8 ply (load range D) instead of 10 ply (load
range E). The towing characteristics went from excellent
to scary. The tire shop fixed the mistake, and all
is well again.

If you are towing a sailplane trailer at 75 MPH behind
a VW Passat, let me know where you're going, so I can
be sure to stay far away. IMHO, not nearly enough
tow vehicle mass, regardless of tires.

At 05:30 03 February 2005, Papa3 wrote:
I recently replaced the Original Equipment Michelin
MXV4 H-rated tires on my
VW Passat 4 motion wagon (Variant for those of you
in Europe) with Dunlop SP
40 A/S all weather radials. Other than lacking a speed
rating, they are the
same dimensions as the originals. Although the
new tires are okay in
regular driving, I've noticed that the towing performance
is much worse.
The car and trailer combination (LS8 in a new Anschau
Komet Euro Trailer)
used to be rock solid up to 75mph; any mild trailer
wag would damp out
immediately. Now, trailer wag can set up at around
65mph, and it seems
less likely to damp out.

I'm assuming that one aspect of speed rated tires must
be a stiffer sidewall
to handle cornering loads. I'm guessing that this
may be a part of the
problem. Anyone else experience similar?

Erik Mann (P3)

Bob C wrote:

If you are towing a sailplane trailer at 75 MPH behind
a VW Passat, let me know where you're going, so I can
be sure to stay far away. IMHO, not nearly enough
tow vehicle mass, regardless of tires.

For what it is worth, the website for VW of Australia indicates that the
towing capacity for the VW Passat is 1300 km (2860 pounds) -- almost
twice the weight of a glider trailer (with glider). Of course, VW
doubtless does not use the same number in the US.

Lorry wrote:
Hi Erik,

From my experience I think you are right on! Trailer tires are usually
a bias belted tire which have a much stiffer side wall.

Take a look at the trailers (both travel trailer and glider trailer)
around you and in the showrooms. You will find almost all of them come
with radial tires. Bias ply tires are cheaper to buy, and that is their
only advantage. Radials are a superior tire, even for trailers. There is
an important difference between trailer rated tires and the typical car
rated tires, even with the same size: the trailer tire _tread_ deflects
less (lower slip angle) for the same side load. There are some other
differences, but that's the one we notice.

A previous
thread cited great improvement by using a 17 inch wheel with low
profile (aspect ratio) tires.

A lower profile will also yield a tread that deflects less.

One way to improve the situation you
describe is to signifigantly increase your rear tire pressure (36-38
psi) and also the pressure of the trailer tires (40 psi).

This will often reduce the "fishtailing", but don't exceed the maximum
pressure rating, shown on the side of the tire. Running a higher
pressure than recommended for the vehicle and tire will likely also
increase your tire wear, increase your braking distance, and definitely
give a harder ride.

To get a
better feel for the situation, try pushing the rear of your vehicle
sideways with a pulsing effort. When your frequency is close to the
natural frequency in that mode you will be surprised at how little
effort it takes to sustain the motion. If you watch the sidewall while
doing this you will notice that the majority, if not all, of the motion
is in the side wall.

The side to side motion you see by doing this is unimportant, and is
about the same at all speeds, unlike true swaying. As attractive as this
theory is, sidewall deflection of this sort isn't what controls the
swaying behind the tow vehicle, which is a dynamic interaction of the
tread deflections (not sidewall) on the tow vehicle and trailer, coupled
to the masses of the vehicles through the hitch.

The increased pressures will increase the natural
frequency and thereby allow a higher speed before the swaying becomes
objectionable.

THe increased pressure reduces the tread deflection for a given side
load - that's why it can help. It might help enough to be useful. I
think, instead, you should carefully consider if these new tires really
are suitable for your vehicle. Do a search using Google's "advanced
groups" search, using these:

AT least one of the words: forester
Group: rec.aviation.soaring
author: Chris

Chris solved his Subaru Forester swaying problem by replacing tires.
Quite dramatic.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Lorry,

Thanks. On the tire pressure suggestion, turns out that the max pressure
for these tires is only 35. I've always been one to run near the top of the
recommended range; I like the stiffer ride and it seems to help gas mileage
noticeably. In this case, even running at the max pressure, it's obvious
that the sidewalls aren't stiff enough.

Looks like another trip to the tire store is in order...

P3


"Lorry" wrote in message
ups.com...
Hi Erik,

One way to improve the situation you
describe is to signifigantly increase your rear tire pressure (36-38
psi) and also the pressure of the trailer tires (40 psi). To get a
better feel for the situation, try pushing the rear of your vehicle
sideways with a pulsing effort.

Hi Erik,

If I remember correctly, the max. press. listed on the side walls of
the original tires supplied on my Olds Silhouette and Cobra trailer is
44 psi. I usually only elevate the tire pressures when going on a long
trip when I need to travel at higher speeds. From experience, this
alows me to cruise about 10 mph faster which helps. However, I agree
that the sidewalls need to be stiffer. The thread I refered to
described their solution which was to buy a pair of aftermarket 17in
wheels (for some model Honda) having the correct 4 bolt pattern and
equiping them with low profile tires. They were elated with the
results. I would do the same if I wasn't so cheap!

Let me know what you decide to do and the results.

Lorry

IMHO, not nearly enough
tow vehicle mass, regardless of tires

Following this logic, I'd be better off using an M-1 Abrahms... :-))

The Passat is a fantastic tow vehicle. With a curb weight of around
3800 lbs, all-wheel drive, stiff suspension, low CG, and a relatively
short coupling between hitch and rear axle, it's a great compromise
between tow vehicle and every day transportation. And with highway
mileage of about 25 (versus what - 16 for the Dodge?), I can still
afford to take a tow when I get to the airport! (and no, I don't really
tow at 75mph, but it is [was] no problem if I needed to for short
bursts with the old setup).

P3

"Papa3" wrote in message
oups.com...
The Passat is a fantastic tow vehicle. With a curb weight of around
3800 lbs, all-wheel drive, stiff suspension, low CG, and a relatively
short coupling between hitch and rear axle, it's a great compromise
between tow vehicle and every day transportation. And with highway
mileage of about 25 (versus what - 16 for the Dodge?), I can still
afford to take a tow when I get to the airport! (and no, I don't really
tow at 75mph, but it is [was] no problem if I needed to for short
bursts with the old setup).

P3


A few years ago I too thought that the Passat wagon looked like a good
choice to tow a glider trailer. When I went to look into buying one I found
out that "Volkswagon recommends that you don't use this vehicle for towing".
I first thought that the dealer was full of it, so I called Volkswagon
myself and, after being handed off a few times, got the definitive answer
that "we (VW) do not recommend that the Passat (or Jetta) be used for towing
and we do not publish any recomended trailer weight limit." Now, I
certainly won't argue with someone who says that he has had good results
using a Passat to tow, but I personally tend to believe the manufacture when
they say that you should not use their automobile for towing.
(This is in the US; perhaps in Europe VW gives a different story.)

Does anyone have experience towing with a Subaru Outback (2005 model
especially)? It bests the Passat wagon in most of the specs that I care
about, including price, and it is rated to tow 2700 lbs (1225 kg).

Michael McNulty wrote:

they say that you should not use their automobile for towing.
(This is in the US; perhaps in Europe VW gives a different story.)

Looking at the outcome of some liability lawsuits in the US, I'm
surprized that there are still manufactorers which recommend their
product for *anything*.

Stefan