FHK11 March Cab

[micramarch]

Well here is my Two pence worth.
The rear discs can cool better as they are open to the air. As you will notice with fast cars, they have vents that actually feed cold air to the brakes. You don't have this benefit with drums as the part the brakes are in contact with is covered.

 

[h701micra]

You don't have this benefit with drums as the part the brakes are in contact with is covered.

Drill holes in the back plates

 

[h701micra]

They both have their merits
Toyota and Subaru saw fit to put both on their cars... discs for the hydraulic side and drums for the handbrake

 

[hilton484]

They both have their merits
Toyota and Subaru saw fit to put both on their cars... discs for the hydraulic side and drums for the handbrake

Now you mention the vectra b I had also had both on the back. Confused the heck out of me at first then decided the discs look like top hats

 

[Enuo]

the reason drums overheat is because unlike a disc brake setup where the caliper presses the friction pad into the disc fairly evenly, on a drum brake the leading edge of one and trailing edge of the other brake shoe are pressed against the inside of the drum. This means that the majority of the friction occurs over a small area, and the shoes themselves overheat (due to localised friction).
There are ways you can improve the cooling;
Painting them matt black will allow them to radiate heat more efficiently
Adding fins, or a finned cover such as:

Will aid in the conducion of heat to the air. You can weld fins to the backplate too to help dissapate heat further.

On our K11's keeping the bias valve and the brakes themselves clean and well adjusted should be enough for most people though. Or you could try bigger drum brakes, I don't know if the rear drums from an almera would fit, they're a tiny bit bigger at least...