On 6/07/2017 5:15 PM, Chaya Eve wrote:
On Thu, 06 Jul 2017 02:08:04 -0400, "Steve W." wrote:

What you feel is known as feathering, one side of the tread block wears
more than the other. If you looked at the end of the block it would
appear as a wedge.

It is commonly caused by improper toe settings and if on one edge only
by improper camber angle as well. BUT it can also be caused by using a
common tire on a vehicle that is driven aggressively. IE high speed
cornering. That places a lot of weight on the outer edge of the tire and
tries to force it to roll under. That will wear the outer edges rapidly.

Now if you had one spot that was "normal" then a wear spot then "normal"
going all the way around the tire that would be cupping. That is
normally a suspension wear problem.

That was a far better answer than I had expected so I appreciate your
expertise. The vehicle was aligned but probably about 2 years ago (while
the tires are about a year old).

The car is driven on a five mile hill every day with scores of hairpins but
it's NEVER driven fast. Those turns are made probably at 20 to 25 MPH (you
can't take the turns any faster and stay on your side of the road).

That means you *are* traveling very fast, at least for the conditions.
What you are saying is that you are leaving no safety margin on each
hairpin. You will definitely be wearing the outer edges of the tyres
doing that.

Could that steep (10% or so) continuously twisting 5-miles each way every
day have caused the "feathering" you explained my "stairstepping" to be?

The hairpins are the reason for the feathering on the outer edges of the
tread. If you adjust to eliminate the feathering on curves, you may see
wear on the inside of the tread instead. It is a suspension geometry
anomaly, a compromise if you will, that you can do little about. If you
only drove on a freeway every day, you would see no feathering. FWD
vehicles tend to fare worse for a number of reasons, one being the
greater SAI angles generally used on them, another being the greater
weight on the steering axles. I get the same issue here with my Toyota
due to the predominance of roundabouts and sharp corners I need to
negotiate. The steering alignment was, and is, spot on.

Toe specs are usually given as a range. Set yours to the favourable side
of the spec range realising that FWD vehicles tend to be positive toe
rather than negative.

--

Xeno