Trailer brakes: electric or override, disk or drum?

Brakes are often the most complex part of a trailer and an increasingly important decision as the weight capacity of the trailer increases. Braking systems can be categorized in a number of ways, first and most importantly is the control method (electric or override), followed by the actuation method (mechanical, hydraulic or electric) and the brake design itself (disk or drum).

These categories are often interrelated, for example, drum brakes are available with any actuation method, but disk brakes are only available with mechanical or hydraulic actuation. Similarly hydraulic actuation can be electric or override, but mechanical is limited to override only. So the benefits and drawbacks of each option have to be weighed as a whole system.

Trailer Brakes - Carbon Equipment


The control method is arguably the most important variable in the braking system, having a large impact on effectiveness and safety. Override brakes work by using a sliding coupling, which acts similar to a brake pedal in a car. When the towing vehicle decelerates, the trailer pushes against the coupling, and the coupling then forces the brakes to be applied through either a mechanical or hydraulic linkage.

The quicker the car decelerates, the harder the trailer pushes against the coupling, and the more force is applied to the brakes. This process is a very effective negative feedback loop that automatically adjusts to keep the force on the tow vehicle constant. This system is very simple and low cost and doesn’t require any special hardware to be installed on the towing vehicle which makes it a popular choice for light trailers.

The simplicity does come with drawbacks though. Since it is a passive system, the trailer brakes don’t receive any signal from the tow vehicle about when the brakes are applied or when the car is reversing. This means the brakes are applied when reversing, requiring the operator to disengage the brakes, then reengage to continue normal operation. It also means that the brakes are only applied when the trailer is already pushing against the vehicle, the brakes cannot help pull the tow vehicle to a stop and the ‘gain’ cannot be adjusted by the operator.

Electric brakes on the other hand typically use a control module installed on the tow vehicle (although trailer mounted units are available). These generally operate by measuring the deceleration of the vehicle and applying the brakes proportionally, either directly or through an electric over hydraulic system. Since electric brake control modules have no feedback from the trailer, the driver must manually adjust the gain (or braking force) to best suit the current conditions. By using a high enough gain, the trailer can brake more than the car keeping tension on the coupling, rather than the trailer pushing the tow vehicle.

The brakes can also be applied independently of the tow vehicle, or in the case of an emergency can automatically be applied if the trailer is disconnected from the tow vehicle, a legal requirement for any trailer over 2,000kg. The disadvantages of an electric braking system are all tow vehicles must have a control module installed, and the effectiveness of the braking system is largely dependent on the quality of the control module, and the ability of the driver to adjust the brakes properly. Typically electric braking systems are less smooth than override braking systems but also much more powerful.

The next factor in the braking process is the actuation method, where there are three standard options, electric, mechanical or hydraulic. This choice often depends primarily on the control system chosen since electric actuation can only use electronic control, and mechanical actuation can only be used with override control. Hydraulic is the only option that is available with both control methods but is only advantageous in some niche situations.

When controlled by an override coupling, hydraulic brakes are far more complex than mechanical brakes but can be installed on both the front and rear axles of a tandem trailer to provide higher braking force. However, due to the breakaway braking requirements, this option is limited to trailers below 2,000kg, which are generally better as a single axle trailer anyway. Hydraulic brakes with electronic control is an option over 2,000kg but require an expensive electric over hydraulic system which converts electrical power into hydraulic power.

This is generally used on trailers where electric drum brakes are not an option, and disk brakes are required. This is a common option on boat trailers. At Carbon Equipment we recommend most users stick to mechanical actuation for override control, and electric actuation for electronic control which are the best options for the vast majority of situations.

The final component of the braking system is the brakes themselves, which are either disk brakes or drum brakes. Disk brakes are more expensive than drum brakes, but typically perform better, are less likely to overheat and do not capture debris and water like drum brakes.

Large Lowering Trailer - Carbon Equipment


The major disadvantage of disk brakes is that they are not currently available for electrically actuated systems, although as electric vehicles become more prominent this may be an option available soon. This makes the choice of brakes simple, for mechanical or hydraulic actuation use disk brakes, while electrical actuation must be drum brakes.

Considering each of the three choices Carbon Equipment believes mechanical override disk brakes are the best option for trailers under 2,000kg where the lower braking power and tendency for the trailer to push the tow vehicle is less prominent, and where the majority of trailers only have one axle anyway.

For high capacity trailers over 2,000kg, electric brakes are the only option to comply with breakaway requirements, but even beyond the legal requirements, they are the best option for the increased braking power needed for safe towing.