The passes
Idaho is mountainous through most of its length, and the routes across it are sustained grades rather than hills.
Descending puts continuous heat into the brakes with no interval to shed it. Pad fade arrives first as the friction material outgasses and its coefficient drops — the pedal feels normal and the car stops less. Then boiling fluid, because brake fluid absorbs water from the atmosphere over years regardless of mileage and boils lower every year. Then a pulsation afterwards from uneven rotor cooling.
Testing brake fluid takes a minute and it is the item that decides how a descent goes.
Climbing is the cooling system's hardest case: high engine load, low road speed so little airflow through the radiator, and thin air at altitude that carries away less heat. Three things working against it at once.
Engine braking is free and it is what the low gears are for.
Off the pavement
A great deal of Idaho's road network is unpaved — forest roads, county roads, and the access to most of the places people actually go.
Gravel adds abrasion to every failure mode. Grit is thrown continuously at every rubber boot, so a split constant-velocity boot ends a joint in weeks. Air filters load at rates no interval anticipates. Brake dust plus grit becomes a grinding paste around caliper slides.
Washboard — the corrugation that forms across a gravel road — works a damper at high frequency and small amplitude for miles at a time. That heats the fluid inside and fades the damping in a way a single impact never does.
A valley growing faster than its roads
Boise, Meridian and Nampa have grown faster than almost anywhere in the country, and the road network has been behind for a decade.
Stop-start commuting is a brake problem: the pads do all the speed control at full vehicle weight, and they are consumed at a mileage rural driving would never approach. Construction and patched surfaces make it a suspension problem too, and a kerbed wheel produces a vibration that survives every rebalance because balance was never the problem.
Range, and no inspection
Idaho runs from genuine winter cold to hot dry summers. Heat destroys batteries — the chemistry accelerates with temperature — and cold reveals the damage on the worst possible morning. Replace on age, before winter.
There is no statewide periodic safety inspection, and emissions testing applies only in the Boise area. Brakes, suspension, steering, tyres and lights are checked by nobody but the owner.
Given mountain descents on one side and unpaved roads on the other, an annual look-over with the wheels off is the substitute: pad thickness measured, brake fluid tested for water, boots checked at full lock, and each wheel rocked at 12 and 6 o'clock.
Checked