Bridges, and the ones with grating
Portland is a river city and the crossings define it. Several of the older bridges carry open steel grating rather than a solid deck, and that surface behaves nothing like asphalt.
In the wet, steel grating gives markedly less grip and it steers the car slightly — the tyre follows the grating pattern. Drivers here learn to hold a steady line and not to brake hard on one, and the ABS learns about it too.
Mechanically, what matters is that the vehicle's grip margin is smallest exactly where the surface is least forgiving. Tyre condition and brake condition are not abstractions on a wet grated deck in December; they are the whole of what you have.
Rain corrodes brakes that never dry
Portland is damp for most of the year — not dramatic rainfall, but persistent, from October into June.
Cast iron rusts whenever it is wet, and a brake rotor is cast iron. On a car driven hard the pad sweeps it clean and it never matters. On a car doing short journeys in permanent damp, the brakes never get hot enough for long enough to dry out.
The result is rotor faces pitted and scaled while still well above minimum thickness, caliper slide pins seized with emulsified grease and water past the boots, and corrosion between the rotor hat and the hub that causes runout and is felt as a pulsation.
A coated rotor is worth more here than the price difference suggests, because the coating protects the hat, the vanes and the edges — exactly the surfaces the pad never sweeps.
The gravel streets nobody expects
Portland has hundreds of blocks of unimproved residential street — genuinely unpaved, inside the city limits, in neighbourhoods that are otherwise urban.
For anyone living on one, that means gravel and potholes for the first and last part of every journey. Grit is thrown at every rubber boot, so a split constant-velocity boot ends a joint in weeks. Air filters load faster than any interval anticipates. And in the wet those streets become deep mud and standing water rather than merely rough.
DEQ, and only here
Emissions testing in Oregon applies in the Portland metropolitan area and the Rogue Valley rather than statewide. There is no periodic safety inspection anywhere in the state.
So a check engine light is a registration problem in Portland and merely a maintenance question in most of Oregon. The test reads the OBD-II system on anything from 1996 onward: a lit lamp fails it outright, and so does a set of readiness monitors that has not completed after somebody cleared a code.
On a car of short damp-weather journeys those monitors can take a long time to set. Fix the fault, then drive several days of mixed use including cold starts and a period at steady speed, then go.
The West Hills
The hills west of downtown are steep, narrow and winding, and a great many people commute over them daily.
That is continuous cornering, which loads outer joints, tie rod ends and the steering rack; and repeated descents, which put heat into brakes that are already compromised by corrosion. Brake fluid absorbs moisture from the air, and in this climate it has had every opportunity.
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