Why signs telling trucks to "Use Lower Gear" on steep hills? (Not physics question)

Why do they have those signs telling trucks to use a lower gear when going downhill? I know a lower gear will hold the truck back but why do you need to have a sign telling the drivers? It’s seem like putting up a sign to brake before every stop sign.

Because people are idiots. Why do they have ‘yield’ signs when chances are you are ALWAYS going to have to yield in those circumstances? same reason I think. For morons.

It’s a way of warning truckers who might be unfamiliar with the area that the hill is longer and steeper than it may appear to be from the top.

Even so, they could brake right? Maybe this is a bit of a physics question after all.

Brakes get hot and become ineffective - or even burn out - if applied for long periods.

Brakes can overheat and fail on steep hills, especially on a fully-loaded 18-wheeler. Lower gear takes the strain off the brakes.

Because,a hill’s grade is measured in percentage,10% 20% etc.,and depending on the state there is probably a specified speed limit at which trucks of various weight configurations are permitted to proceed down the hill.The "Trucks use Lower Gear,"is a preliminary warning sign advising them to gear down BEFORE they reach the crest of the hill,or they may be in too high a gear to safely decend said hill without overheating the brakepads.

You have to realize that the experience a trucker has in a vehicle weighing 70,000 lbs and the experience that you might have in your passenger car weighing somewhere between 2,500 lbs (Mazda Miata) and 5,500 lbs (unladen Chevy Suburban) is going to be radically different.
In a bad circumstance, the trucker may wind up running the brakes quite hard in addition to gearing down. Apparently the gearing down does not always suffice.

I hope a follow up is kosher. Do those grade percentages correspond in some way to an average angle of slant? For example, does 10% mean 10% of a 45 degree angle?

Anyone who has driven a manual transmission car is familiar with compression slowing. By shifting into lower gears you are balancing your truck in a state of constant “compression slowdown” so that you maintain a safe downhill speed without taxing your brakes.

Mostly a mater of proper gear selection. If in need of additional braking power most heavy vehicles are also equipped with a Jacobsen Engine brake and or transmission retarders

Percent grade is the tangent of the angle multiplied by 100. For the trigonometry-impaired, it is the rise divided by the run multiplied by 100.

For example, a slope that rises one foot for every ten feet of horizontal travel has a grade of ten percent. If it rose a foot and a half for every ten horizontal feet it would have a grade of fifteen percent.

A grade of ten percent is about 5.7 degrees. Fifteen percent is about 8.5 degrees, and twenty percent is about 11.3 degrees. A hundred percent is 45 degrees.

Nope, a 10% grade means it drops or rises a foot for every 10 vertical feet. You’ll have to break out your calculator, computer or trig tables to get from “percentage” to “angle”. 10% is about a 5.7 degree slope.

Should be driveline retarders…

A 10% grade means that for every 100 feet of horizontal distance, the road drops 10 feet in elevation. This corresponds to about a 5 degree downward slope.

Make that 10 HORIZONTAL feet, of course, and Mr. Lichtman, a worthy alumnis of Ingres (hello, Jeff), snuck in ahead of me.

A yield sign is a notification that one does not have the right of way at an intersection. It overrides the usual rules for determining who gets to go first at the intersection and helps determine guilt if there is a collision. I don’t know why you think the signs are for morons.

A 10% slope means it drops 10 feet for every 100 feet.

Ever head east on I-70 into Denver? There’s many huge signs with flashing lights saying things like “Steep Grade next 7 miles, Truckers use lower gear.” Halfway down there’s a sign that says “Truckers don’t be fooled, steep grades ahead, use lower gear.”

I suspect Denver got tired of scraping truckers off the road at the bottom of the hill.

Crud - botched the tags. Sorry.