"chris" wrote in message
om...
Here is the feedback on my trailer towing problem.
I thought I'd make a detailed write up to share what I learned with
others.

I was waiting until I gave a real towing trip as proof that this fix
worked. I recently drove from Atlanta up to the Sequatchie Valley in
TN. This included highway driving as well as crossing Signal Mountain
on a steep winding road. The Forester XT now is a good safe tow
vehicle. The turbocharged engine is really powerful, during hill
climbs I had to downshift not because it was too weak, but because it
wanted to race up the hills.

As I suspected it was indeed the tires at fault. For some reasons
the auto manufacturers insist on pinching pennies and putting on lousy
tires when for ~$20 of cost to them they could impress their customers
with a much higher quality ride.

The original tires were Yokohama Geolander G900 P215/60 R16 94H.
These are really poor quality, I suspect that they are the very
minimum standard of the H speed rating. This is an all season tire.

I replaced them with Toyo Proxes TPT P225/55 R16 95V.
These are much higher quality overall, [as well as the ratings for
treadwear, temperature & traction]. The key was switching from poor
"H" to good "V" rated tires. This gave a much stiffer sidewall.
The tire size is also 10mm wider [225 vs 215 with a 5% shorter
sidewall 55 vs 60]. [2% net reduction in diameter].
The tread compound is also harder, more like a sports car tire.

All these changes eliminated the uncontrolled harmonic
swaying/fishtailing that I experienced when towing my trailer with the
tall tires on the tow vehicle. During normal driving the ride is
stiffer, this is fine with me, the cornering is much improved.


Years ago I read that every force your car generates, acceleration,
braking and cornering etc. is transmitted through the tires - don't
skimp, they are one of the most components of the vehicle.
My advice to others that are experiencing swaying:
Invest in good quality tires.
Upgrade the speed rating to get a stiffer sidewall. [from S or T to H,
from H to V]
Consider shortening the sidewall with a lower ratio.
Increase the tire pressure.

Thanks for your report. I have one question about what you've written. I
understand your conclusions related to tire aspect ratio, but why do you
relate tire speed rating to sidewall stiffness? My understanding was that
the speed rating primarily involved tires capacity to deal with heat. Could
there not also be T or H rated tires with relatively stiff sidewalls?

Thanks.