On Tuesday, March 13, 2018 at 7:55:15 PM UTC-4, Eric Greenwell wrote:
Bruce Hoult wrote on 3/4/2018 8:35 AM:
Sidewall stiffness helps. Either inherent -- crossplys are better than radials, all else being equal -- or created by pumping them up to the maximum pressure.

Realistically, the only time you can choose crossply (aka "bias ply") tires is in
the "ST" category (trailer tires), because they aren't commonly available for
passenger cars. The steel belt gives the tire tread more lateral stiffness than a
the same size non-belted crossply tire, and consequently more stability to the
trailer. There are other very good reasons radials are the most common car and
trailer tire; the only advantage of a non-belted trailer tire is lower price.

I actually did the experiment last year, putting same size radials and bias ply
tires on my trailer. The radials let me tow about 7-10 mph faster. Contrary to
"common knowledge", the radial ST tire deflected less laterally than the same size
bias ply ST tire. A similar (not identical) size LT radial tire had even less
deflection than the other two when tire pressures were set for the same load rating.

It's a small sample of the tire universe, but illustrates choosing by assumed
sidewall stiffness is not a good way to choose tires.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)

I agree that radials work well from my experience. I don't actually understand why people think the tires on the trailer are the problem. The trailer tire sidewalls are not flexing in my experience. In my experience the tires at the rear of the tow vehicle are the critical item.
The trailer tires/axel are the hinge point, however all the resistance from swaying needs to happen at the hitch and forward.

I had a Subaru Forester that had very soft sidewall H rated tires. The komet trailer got extremely unstable at 45mph and higher.

(Without a trailer on even) I could not believe that tire got an H rating it was really soft, you could push sideways on the hitch and watch the entire vehicle oscillate. I thought I was going to have to sell the Forester.

Higher inflation especially of the rear tires helped some.

Instead I changed to a stiff sidewall V rated good quality tire then i could tow very stable up to 85+mph. I also kept the rear tires inflated about 5 psi higher than the fronts.

No change of trailer tires was involved - I usually ran radials on the trailer.

Chris