On Sunday, June 19, 2016 at 7:44:33 PM UTC-4, Henning Schröder wrote:
I'm on Tire Rack and need to make a choice to help a friend.
What's the *practical* difference of 10mm wider tread?

1. This SUV is a dozen years old & has never been off road
2. This SUV is used like a car & never carries a heavy load
3. What matters to the owner is economy & safety

From the standpoint of economy (e.g., miles per tire), I don't
know if a 10mm wider tire will last longer or shorter. Do you?

From safety, I "guess" that 10mm more of tread width is safer,
but the driver is a little old lady (literally) in a no-snow
state, so, traction isn't really a problem.

Any idea what's best?

Stock OEM is 225x75R15
Current tires are 235x75R15 but I'm replacing all four.

What difference (practically) does 10mm make?

Not much. With that small difference they will fit. In terms of
how long they last, won't make any difference. I recall doing some
calcs back in college that showed about one molecule worth of rubber
comes off each revolution. Certainly that small difference isn't
going to affect how many miles they last. If snow is a consideration,
wider is usually worse for traction, because the tire can't dig
throw the snow to the pavement as easily. Wider is also more susceptible
to hydroplaning. But on dry pavement, wider has more traction.