Discussion
Why do they exist?
A disc seems like such a simple, obvious and effective way of slowing or stopping a rotating wheel that it's hard to imagine how anyone would come up with the drum brake. Harder still to imagine why many brand new cars in 2012 still have drum brakes.
So there must be some good reason. Something to do with materials? Some quirk of hydraulics? What is the reason?
A disc seems like such a simple, obvious and effective way of slowing or stopping a rotating wheel that it's hard to imagine how anyone would come up with the drum brake. Harder still to imagine why many brand new cars in 2012 still have drum brakes.
So there must be some good reason. Something to do with materials? Some quirk of hydraulics? What is the reason?
Cost.
Most of the braking is carried out by the front axle due to weight shift so therefore discs really aren't needed on the rear of most cars - how many cars have vented discs on the rear for example?
Drums are cheap to manufacture and it's easy/cheap to incorporate the handbrake mechanism as well.
Most of the braking is carried out by the front axle due to weight shift so therefore discs really aren't needed on the rear of most cars - how many cars have vented discs on the rear for example?
Drums are cheap to manufacture and it's easy/cheap to incorporate the handbrake mechanism as well.
+1, I'd guess incorporating the handbrake is one of the main reasons (less complex)
http://en.wikipedia.org/wiki/Drum_brake#Advantages
http://en.wikipedia.org/wiki/Drum_brake#Advantages
I think all of the above are valid answers as to why drum brakes are still fitted to cars, but to me, the OP appeared to ask how anyone even came up with the drum brake when the disc brake seems to be a far more logical solution for stopping a rotating wheel/ axle.
Interesting question though. Maybe it's a case of sometimes, the simplest solution is hardest to see
Interesting question though. Maybe it's a case of sometimes, the simplest solution is hardest to see
From wikipedia as I can't be bothered writing it out myself:
Drum brakes are used in most heavy duty trucks, some medium and light duty trucks, and few cars, dirt bikes, and ATV's. Drum brakes are often applied to the rear wheels since most of the stopping force is generated by the front brakes of the vehicle and therefore the heat generated in the rear is significantly less. Drum brakes allow simple incorporation of a parking brake.
Drum brakes are also occasionally fitted as the parking (and emergency) brake even when the rear wheels use disk brakes as the main brakes. The vast majority of rear disc braking systems use a parking brake in which the piston in the caliper is actuated by a cam or screw. This compresses the pads against the rotor. However, this type of system becomes MUCH more complicated when the rear disc brakes use fixed, multi-piston calipers. In this situation, a small drum is usually fitted within or as part of the brake disk. This type of brake is also known as a banksia brake.
In hybrid vehicle applications, wear on braking systems is greatly reduced by energy recovering motor-generators (see regenerative braking), so some hybrid vehicles such as the GMC Yukon hybrid and Toyota Prius (except the third generation) use drum brakes.
Disc brakes rely on pliability of caliper seals and slight runout to release pads, leading to drag, fuel mileage loss, and disc scoring. Drum brake return springs give more positive action and, adjusted correctly, often have less drag when released.
Certain heavier duty drum brake systems compensate for load when determining wheel cylinder pressure; a feature unavailable when disks are employed. One such vehicle is the Jeep Comanche. The Comanche can automatically send more pressure to the rear drums depending on the size of the load, whereas this would not be possible with disks.
Due to the fact that a drum brakes friction contact area is at the circumference of the brake, a drum brake can provide more braking force than an equal diameter disc brake. The increased friction contact area of drum brake shoes on the drum allows drum brake shoes to last longer than disc brake pads used in a brake system of similar dimensions and braking force. Drum brakes retain heat and are more complex than disc brakes but are often the more economical and powerful brake type to use in rear brake applications due to the low heat generation of rear brakes, a drum brakes self applying nature, large friction surface contact area, and long life wear characteristics(%life used/kW of braking power).
Although drum brakes are often the better choice for rear brake applications in all but the highest performance applications, vehicle manufactures are increasingly installing disc brake system at the rear wheels. This is due to the popularity rise of disc brakes after the introduction front ventilated disc brakes. Front ventilated disc brakes performed much better than the front drum brakes they replaced. The difference in front drum and disc brake performance caused car buyers to purchase cars that also had rear disc brakes. Additionally rear disc brakes are often associated with high performance race cars which has increased their popularity in street cars. Rear disc brakes in most applications are not ventilated and offer no performance advantage over drum brakes. Even when rear discs are ventilated, it is likely that the rear brakes will never benefit from the ventilation unless subjected to very high performance racing style driving.
Drum brakes are used in most heavy duty trucks, some medium and light duty trucks, and few cars, dirt bikes, and ATV's. Drum brakes are often applied to the rear wheels since most of the stopping force is generated by the front brakes of the vehicle and therefore the heat generated in the rear is significantly less. Drum brakes allow simple incorporation of a parking brake.
Drum brakes are also occasionally fitted as the parking (and emergency) brake even when the rear wheels use disk brakes as the main brakes. The vast majority of rear disc braking systems use a parking brake in which the piston in the caliper is actuated by a cam or screw. This compresses the pads against the rotor. However, this type of system becomes MUCH more complicated when the rear disc brakes use fixed, multi-piston calipers. In this situation, a small drum is usually fitted within or as part of the brake disk. This type of brake is also known as a banksia brake.
In hybrid vehicle applications, wear on braking systems is greatly reduced by energy recovering motor-generators (see regenerative braking), so some hybrid vehicles such as the GMC Yukon hybrid and Toyota Prius (except the third generation) use drum brakes.
Disc brakes rely on pliability of caliper seals and slight runout to release pads, leading to drag, fuel mileage loss, and disc scoring. Drum brake return springs give more positive action and, adjusted correctly, often have less drag when released.
Certain heavier duty drum brake systems compensate for load when determining wheel cylinder pressure; a feature unavailable when disks are employed. One such vehicle is the Jeep Comanche. The Comanche can automatically send more pressure to the rear drums depending on the size of the load, whereas this would not be possible with disks.
Due to the fact that a drum brakes friction contact area is at the circumference of the brake, a drum brake can provide more braking force than an equal diameter disc brake. The increased friction contact area of drum brake shoes on the drum allows drum brake shoes to last longer than disc brake pads used in a brake system of similar dimensions and braking force. Drum brakes retain heat and are more complex than disc brakes but are often the more economical and powerful brake type to use in rear brake applications due to the low heat generation of rear brakes, a drum brakes self applying nature, large friction surface contact area, and long life wear characteristics(%life used/kW of braking power).
Although drum brakes are often the better choice for rear brake applications in all but the highest performance applications, vehicle manufactures are increasingly installing disc brake system at the rear wheels. This is due to the popularity rise of disc brakes after the introduction front ventilated disc brakes. Front ventilated disc brakes performed much better than the front drum brakes they replaced. The difference in front drum and disc brake performance caused car buyers to purchase cars that also had rear disc brakes. Additionally rear disc brakes are often associated with high performance race cars which has increased their popularity in street cars. Rear disc brakes in most applications are not ventilated and offer no performance advantage over drum brakes. Even when rear discs are ventilated, it is likely that the rear brakes will never benefit from the ventilation unless subjected to very high performance racing style driving.
DanielC4GP said:
From wikipedia as I can't be bothered writing it out myself:
Drum brakes are used in most heavy duty trucks, some medium and light duty trucks, and few cars, dirt bikes, and ATV's. Drum brakes are often applied to the rear wheels since most of the stopping force is generated by the front brakes of the vehicle and therefore the heat generated in the rear is significantly less. Drum brakes allow simple incorporation of a parking brake.
Drum brakes are also occasionally fitted as the parking (and emergency) brake even when the rear wheels use disk brakes as the main brakes. The vast majority of rear disc braking systems use a parking brake in which the piston in the caliper is actuated by a cam or screw. This compresses the pads against the rotor. However, this type of system becomes MUCH more complicated when the rear disc brakes use fixed, multi-piston calipers. In this situation, a small drum is usually fitted within or as part of the brake disk. This type of brake is also known as a banksia brake.
articulated lorrys since the late ninties have been switching to disc's , one heel of a difference its made, the reasons for drums up to the ninties are weight on trucks, as someone has commented earlier my first car was drums all round, no servo....................jesus.
In hybrid vehicle applications, wear on braking systems is greatly reduced by energy recovering motor-generators (see regenerative braking), so some hybrid vehicles such as the GMC Yukon hybrid and Toyota Prius (except the third generation) use drum brakes.
Disc brakes rely on pliability of caliper seals and slight runout to release pads, leading to drag, fuel mileage loss, and disc scoring. Drum brake return springs give more positive action and, adjusted correctly, often have less drag when released.
Certain heavier duty drum brake systems compensate for load when determining wheel cylinder pressure; a feature unavailable when disks are employed. One such vehicle is the Jeep Comanche. The Comanche can automatically send more pressure to the rear drums depending on the size of the load, whereas this would not be possible with disks.
Due to the fact that a drum brakes friction contact area is at the circumference of the brake, a drum brake can provide more braking force than an equal diameter disc brake. The increased friction contact area of drum brake shoes on the drum allows drum brake shoes to last longer than disc brake pads used in a brake system of similar dimensions and braking force. Drum brakes retain heat and are more complex than disc brakes but are often the more economical and powerful brake type to use in rear brake applications due to the low heat generation of rear brakes, a drum brakes self applying nature, large friction surface contact area, and long life wear characteristics(%life used/kW of braking power).
Although drum brakes are often the better choice for rear brake applications in all but the highest performance applications, vehicle manufactures are increasingly installing disc brake system at the rear wheels. This is due to the popularity rise of disc brakes after the introduction front ventilated disc brakes. Front ventilated disc brakes performed much better than the front drum brakes they replaced. The difference in front drum and disc brake performance caused car buyers to purchase cars that also had rear disc brakes. Additionally rear disc brakes are often associated with high performance race cars which has increased their popularity in street cars. Rear disc brakes in most applications are not ventilated and offer no performance advantage over drum brakes. Even when rear discs are ventilated, it is likely that the rear brakes will never benefit from the ventilation unless subjected to very high performance racing style driving.
articulated lorrys now have all round disc's, since the ninties trucks have been moving this way, weight was a big issue, its made one hell of a difference in the way they stop, as commented earlier my first car, escort mk1 had drums al round, with no servo..................jesus.Drum brakes are used in most heavy duty trucks, some medium and light duty trucks, and few cars, dirt bikes, and ATV's. Drum brakes are often applied to the rear wheels since most of the stopping force is generated by the front brakes of the vehicle and therefore the heat generated in the rear is significantly less. Drum brakes allow simple incorporation of a parking brake.
Drum brakes are also occasionally fitted as the parking (and emergency) brake even when the rear wheels use disk brakes as the main brakes. The vast majority of rear disc braking systems use a parking brake in which the piston in the caliper is actuated by a cam or screw. This compresses the pads against the rotor. However, this type of system becomes MUCH more complicated when the rear disc brakes use fixed, multi-piston calipers. In this situation, a small drum is usually fitted within or as part of the brake disk. This type of brake is also known as a banksia brake.
articulated lorrys since the late ninties have been switching to disc's , one heel of a difference its made, the reasons for drums up to the ninties are weight on trucks, as someone has commented earlier my first car was drums all round, no servo....................jesus.
In hybrid vehicle applications, wear on braking systems is greatly reduced by energy recovering motor-generators (see regenerative braking), so some hybrid vehicles such as the GMC Yukon hybrid and Toyota Prius (except the third generation) use drum brakes.
Disc brakes rely on pliability of caliper seals and slight runout to release pads, leading to drag, fuel mileage loss, and disc scoring. Drum brake return springs give more positive action and, adjusted correctly, often have less drag when released.
Certain heavier duty drum brake systems compensate for load when determining wheel cylinder pressure; a feature unavailable when disks are employed. One such vehicle is the Jeep Comanche. The Comanche can automatically send more pressure to the rear drums depending on the size of the load, whereas this would not be possible with disks.
Due to the fact that a drum brakes friction contact area is at the circumference of the brake, a drum brake can provide more braking force than an equal diameter disc brake. The increased friction contact area of drum brake shoes on the drum allows drum brake shoes to last longer than disc brake pads used in a brake system of similar dimensions and braking force. Drum brakes retain heat and are more complex than disc brakes but are often the more economical and powerful brake type to use in rear brake applications due to the low heat generation of rear brakes, a drum brakes self applying nature, large friction surface contact area, and long life wear characteristics(%life used/kW of braking power).
Although drum brakes are often the better choice for rear brake applications in all but the highest performance applications, vehicle manufactures are increasingly installing disc brake system at the rear wheels. This is due to the popularity rise of disc brakes after the introduction front ventilated disc brakes. Front ventilated disc brakes performed much better than the front drum brakes they replaced. The difference in front drum and disc brake performance caused car buyers to purchase cars that also had rear disc brakes. Additionally rear disc brakes are often associated with high performance race cars which has increased their popularity in street cars. Rear disc brakes in most applications are not ventilated and offer no performance advantage over drum brakes. Even when rear discs are ventilated, it is likely that the rear brakes will never benefit from the ventilation unless subjected to very high performance racing style driving.
Edited by rumple on Sunday 15th January 19:44
Scuffers said:
drums can be more powerfull, have a bigger friction area, last longer, etc.
Most trucks have drums for this reason alone (brake feel is less important when your dealing with 18 wheels via air-brakes.)
Majority of new trucks are now on discs. They've taken so long to catch up as they've had lots of problems with cracked discs during development. Shattered truck brake discs are not an uncommon sight on the motorways.Most trucks have drums for this reason alone (brake feel is less important when your dealing with 18 wheels via air-brakes.)
Why shouldn't they exist? In every modern car to which they are fitted, they are adequate and fit for purpose- even in my Caterham race car. Only problem is having to adjust them every once in a while. As others have said, the vast majority of braking is done by the front axle, and I doubt my car would be any faster over a lap with discs on the back.
The main disadvantage of drums for me, and the main reason I prefer discs is that, despite working fine, they shoes and inside of the drum can deteriorate dangerously. I've taken some apart where the friction material just falls off, and have suffered at least one car spinning due to a locked rear drum due to this fault.
At least on a disc system it's easier to have a quick look to determine overall condition.
At least on a disc system it's easier to have a quick look to determine overall condition.
http://www.motorera.com/history/hist07.htm
Interesting site with lots about brakes. I guess we only had drums because they were self-servoing, which made them easier to operate by rod or cable.
Interesting site with lots about brakes. I guess we only had drums because they were self-servoing, which made them easier to operate by rod or cable.
Noesph said:
+1, I'd guess incorporating the handbrake is one of the main reasons (less complex)
http://en.wikipedia.org/wiki/Drum_brake#Advantages
Both at the rear means I can use the parking brake without risking any marking of the disks after a hard drive. I can't believe the GTO is the only car with this set-up.http://en.wikipedia.org/wiki/Drum_brake#Advantages
driverrob said:
Both at the rear means I can use the parking brake without risking any marking of the disks after a hard drive. I can't believe the GTO is the only car with this set-up.
Both on the rear is just pointless complication IMO.Normally the drum ends up being too small to act as a decent parking brake and the duplication means more maintenance and expense.
I'd much rather have good size drums on the rear than only discs or a hybrid system.
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