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Currently I own a Mk5 Astra SRi, however I am looking to sell this and buy a Ford Focus Mk2.

The other day I looked at a Ford Focus Zetec Mk2. My understanding is that Zetec is sort of the ford equivalent of an Astra SRi (given that ST is the equivalent of a VXR).

The only thing that really threw a spanner in the works for me was the drum brakes on the back wheels. I had a look around and found that the latest two models of VW Polo have discs, as do Golf's from Mk4 onwards, as do most Seat Leons, and even Prius's!

Why on earth would a reputable company still fit this ancient technology, when most modern cars are using rear disc brakes? And, how much of an impact do drum brakes have in comparison to disc brakes?

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4 Answers 4

up vote 8 down vote accepted

Drum brakes are cheaper to manufacture than disc brakes, because there are fewer moving parts and because in the rear the parking brake (which often works by a drum-and-shoe mechanism even on four-wheel-disc-equipped cars) can share a drum with the "regular" brakes.

All other things being equal, discs work better than drums, especially in wet conditions.

However, in this case, in regular driving you will very likely never notice a difference. Most of the braking effort, even in a panic stop, comes from the front wheels. So front discs are much better than front drums, but rear drums are not much worse than rear discs.

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4  
for what it's worth, plenty of disc-brake-equipped cars do not use drum parking brakes. –  mac Jun 18 '13 at 18:09
    
@mac: Good point. The only cars I've seen like that are '80s Saabs, but I can believe there are others. Edited my answer. –  dodgethesteamroller Jun 18 '13 at 18:44
    
Adding on to this - the braking percentages are something on the order of 70Front/30Rear or 80Front/20Rear in some cases. –  jsanc623 Jun 18 '13 at 21:14
    
More examples. 2g Mitsubishi Eclipse uses drum in disc setup for parking brake. MKII MR2 uses a special disc only parking brake mechanism. –  Brian Knoblauch Jun 20 '13 at 18:45
    
BMW 318 TDS E36 (1996) Compact has rear drum brakes –  Skippy Fastol Feb 4 at 16:35

Tom & Ray point out that drum brakes can serve double-duty as the parking brake. Other people around the web believe it has to do with retooling costs.

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The rear brakes hardly contribute to stopping your car. They do between 20% and 30% of the work, so they can be cheap without compromising your safety or stopping distance. Mind you, drum brakes last much MUCH longer than discs. I have a Vauxhall Corsa B that has done 100k miles (160k kilometers) and the drums and shoes are still good for at least another 50% of that distance. See it as Ford saving you money. If you want to increase your braking performance, spend some extra money on pads and rotors up front the next time you have to change them. And stay away from slotted and cross-drilled rotors if you don't do lots of high speed stops. A smooth rotor has a larger contact area, so gives better stopping performance in normal conditions. Slotted and drilled rotors are a compromise between performance and better cooling characteristics for sport and track applications.

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"Slotted and drilled rotors are a compromise between ..." - they're not really a compromise when you take in to account the full set up of much larger pads and rotors. Interesting point nonetheless. –  andrewb Oct 5 '13 at 23:34
    
Understood. But your average ricer doesn't go for larger rotors or pads, they just have the OEM stuff drilled, which is stupid. –  Juann Strauss Oct 7 '13 at 10:21

Besides being cheap to manufacture, lighter, being easier to use as a parking brake, and being of limited usefulness on a front engine car to begin with... Drum brakes also have the advantage of being "no drag". When they're off, they're completely off. Compare to disc brakes where there can still be a little bit of drag as there's no mechanism to pull the pads off the disc when not under braking...

It's a common thing for drag race cars that come with disc brakes to have them removed and replaced with drums for the weight and drag reasons.

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