Disk or drum brakes ?

[Renze]

I'm talking full air brakes here. Electric brakes are next to non-existent in Europe. They probably will be, untill the automotive industry adopts the 48 Volt standard for on board electricity like airco compressor, electric windows, and keep the small things like lights just 12 volt like it used to be.
some manufacturers are talking about it, and it is expected that many car makers get a split 12/48 volt system in cars within 10 years.

So, which will function better, if we keep the way of actuating out of it ?

My boss used to have a Ford Sierra. Every time he braked hard in rainy weather and then drove through water with hot disks, they warped. After 3 sets of new disks, he decided it was time to change for a car with better brakes.

Over here in Europe, i've never seen a low bed trailer with disk brakes. Only flat deck and box trailers.

 

[patrick_g]

Just stirin' the pot... Why do you suppose that the metal of drums would not rust as bad as disk rotors while just setting for a looooong time?

Pat

 

[Egon]

I have been atinkin???

If I'd like to stop real quick or slow down on a long steep hill the disk brakes are the way to go.

If I want an emergency brake that works well in cold/wet conditions and does not freeze solid I'd go for the drum brakes.

And if I had my way all driving wheels would mounted inboard.

 

[wushaw]

Just stirin' the pot... Why do you suppose that the metal of drums would not rust as bad as disk rotors while just setting for a looooong time?

Pat

Disk are completely exposed to the elements.
Have ya ever gone to a wrecking yard an pulled either that has not been submerged in water?

 

[Renze]

Another thing i've heard from a drum brake axle salesman: Disk brake pads get "lazy" if you dont use them to full capacity, which means they loose functionality after a while of light duty use.

 

[wushaw]

Lazy??? What??? I have never experienced, seen or heard of a "lazy" disk brake pad.

 

[patrick_g]

How long do disk brakes have to be on vacation before they get lazy? Our family sedan is a Prius and the way I drive it maximizes the regenerative braking and minimizes the use of the disk brakes. We have almost 30,000 miles on it and the "real" brakes have seen about as much service as if it had been driven 5,000 or less. Unless setting the parking brake prevents laziness I can't imagine how I would have avoided it in my style of use. Unless it is more imagined than real or something that is rare and unusual.

Hmmmm, lets see now... a drum brake salesman said...

Pat

 

[Renze]

They told me that disk brake pads, when only used slightly, get "glassy" and hard...
For my personal experience, it's the other way around: I only had this "glassy" bake hardened brake pads on my previous car, a volvo 440 turbodiesel, with solid brake disks. I assume the brakes got too hot and the brake pads got overheated, so they lost effectiveness. (due to my driving style i have to say, going from 160 to 60 in seconds, beats the crap out of them brakes)
My current car, a Volvo 850 2.5 TDI, has vented disks all around. Stopping power is just great, compared to the 440 (which is an entry level Volvo, the predecessor of the S40 and never made it outside europe)

I think with disk brakes, the biggest issue is that too small brake disks get too hot, even though they do have the nominal brake torque. it's easy to build a disk brake that has more brake capacity than cooling capacity, which means "glassy" brake pads and warped rotors, because an enthusiastic designer wanted to save on weight by taking a too small brake disk.

The drum brake designer doesnt get in this risk zone, because he needed the steel anyways, to withstand the purely mechanical forces of the expanding brake shoes. The disk brake has a claw, pushing the brake pads on from both sides, equalling these bend forces to zero.

where i am going is, the drum brake designer needed the steel anyways to cope with the mechanical forces of the expanding brake shoes, and designs to the mechanical limit of the brake.
The disk brake designer doesnt have to count for any bend forces, so the mechanical force is not the limiting factor. For disk brakes, the amount of heat that the disks can dissipate is the limiting design factor.

 

[patrick_g]

Renze, You are right on target. Super thin rotors will generate the same braking force as thick well ventilated ones (for a little while.) Thin is cheap so guess where the bean counters force the design to go.

Pat

 

[Renze]

Another thing is rental trailers: Companies set the trailer brake valve higher, so the trailer does the stopping, so the brakes of the hired trailer wear excessive, and the truck brakes (which are replaced at the transport company's own cost instead of on the rental companies expense) are saved.

To me, drum brakes still seem the most reliable bet because you cant go wrong.