UK Garage Brake Testing Explained

Ensuring your vehicle's braking system is in peak condition is paramount for road safety. In the UK, garages and testing stations employ specific equipment to rigorously assess the performance of your car's brakes. This article delves into the types of brake testers you're likely to encounter during an inspection, explaining how they work and why they are crucial for maintaining your vehicle's roadworthiness.

Understanding Brake Testing in the UK

Brake testing is a fundamental part of vehicle maintenance and regulatory checks, particularly for the Ministry of Transport (MOT) test in the UK. The primary objective is to determine the effectiveness and balance of a vehicle's braking system. This involves measuring the braking effort exerted by each wheel and the overall braking efficiency of the vehicle. Several types of equipment are used to achieve this, each with its own methodology.

Roller Brake Testers: The MOT Stalwart

The most prevalent type of brake tester found in UK garages, especially within MOT inspection lanes, is the roller brake tester. This sophisticated piece of equipment allows for a dynamic assessment of a vehicle's braking system while the vehicle itself remains stationary.

How Roller Brake Testers Work

A roller brake tester typically consists of a mechanical floor unit housing electrical motors, sets of three measuring rollers for each wheel, brake force transducers, and various safety sensors. The driving rollers, powered by electric motors and a gearbox, rotate at a low, controlled speed. When the driver applies the vehicle's brakes, this action creates a reaction force against the electric motors. This force is then measured by an electric transducer, which uses strain gauges to detect the individual braking forces applied by each wheel. These measurements are crucial for calculating the braking force and identifying any imbalances.

To ensure accuracy, the rollers are designed with a large diameter to minimise the impact of tyre flex and mechanical relaxation. The roller surface is coated with a durable material that provides excellent grip and wear resistance, performing reliably in both wet and dry conditions. A smaller, third roller positioned between the main driving rollers serves a dual purpose: it acts as a safety device, preventing the motors from starting unless a vehicle is correctly positioned, and it detects tyre slippage, crucial for obtaining accurate readings before a pre-set time limit.

During the test, a computer system records the brake force values. It then calculates the imbalance between the left and right brake forces on an axle, as well as the overall efficiency of both the service brake (foot brake) and the parking brake. This calculation can be made more accurate if the vehicle's weight is known, either entered manually or via an integrated weighing system.

Advantages of Roller Brake Testers

• Comprehensive Assessment: Provides detailed data on individual wheel braking forces and overall efficiency.
• MOT Compliance: The standard equipment for MOT testing.
• Safety: Carried out in a controlled environment.

Disadvantages of Roller Brake Testers

• Tyre Wear: Can cause minor tyre wear if not used correctly.
• Cost: More expensive to install and maintain than simpler methods.

Plate Brake Testers: An Accurate Alternative

While less common than roller testers in the UK, plate brake testers offer another method for measuring a vehicle's braking system performance. These testers are considered highly accurate and operate on a dynamic principle.

How Plate Brake Testers Work

A plate brake tester comprises two parallel measuring plates mounted on force transducers. The vehicle drives over these plates, and when the brakes are applied, the plates move slightly due to the braking action. This controlled slip allows for the calculation of braking force. By measuring the voltage changes in the force transducers beneath each plate, the system can determine the braking force for each wheel and identify any imbalances between the left and right sides of an axle.

The dynamic nature of plate brake testers makes them a precise tool for measurement. In countries like Australia and New Zealand, they are gaining popularity as a superior alternative to basic decelerometers. Their advantages include accuracy, speed of measurement, ease of use, and, importantly, enhanced safety by eliminating the need to test brakes on public roads.

Advantages of Plate Brake Testers

• High Accuracy: Offers precise measurements of braking forces.
• Dynamic Testing: Simulates real-world braking conditions more closely.
• Safety: Reduces the need for on-road testing.

Disadvantages of Plate Brake Testers

• Less Common in UK: Not the standard for MOT tests.
• Installation Complexity: Can require more involved installation.

Decelerometers: The Portable Indicator

Decelerometers are handheld devices used to measure the dynamic braking forces during a road test. Essentially an accelerometer, they calculate braking efficiency by measuring the forces experienced during a vehicle's deceleration.

How Decelerometers Work

A decelerometer is typically mounted within the vehicle, often on the dashboard or windscreen. As the driver applies the brakes, the device measures the rate of deceleration. This reading provides a quick and easy indication of the brake performance. While useful for a rapid assessment, decelerometers are generally considered indicators of acceptable brake performance rather than definitive measurement tools.

If a decelerometer reading falls below acceptable levels, it signals a need for further investigation using a more sophisticated tester, such as a roller brake tester or a plate brake tester. They are a valuable tool for initial checks or for assessing the general feel of the brakes.

Advantages of Decelerometers

• Portability: Easy to use and transport.
• Speed: Provides a quick initial assessment.
• Cost-Effective: Generally less expensive than roller or plate testers.

Disadvantages of Decelerometers

• Lower Accuracy: Less precise than roller or plate testers.
• Road Testing Required: Necessitates a road test, which can be less safe.
• Limited Data: Does not provide detailed information on individual wheel performance.

Comparing Brake Testing Methods

Here's a brief comparison of the main types of brake testers used:

Frequently Asked Questions (FAQs)

What is the most common brake tester used in UK garages?

The roller brake tester is the most common type of brake tester used in UK garages, particularly for MOT inspections.

Are plate brake testers accurate?

Yes, plate brake testers are considered very accurate and provide precise measurements of braking forces.

Can a decelerometer fail an MOT test?

A decelerometer itself doesn't fail an MOT test. However, if a decelerometer indicates poor brake performance, it will likely lead to further testing on a roller or plate brake tester, which could result in a failure if the brakes do not meet the required standards.

Why is brake balance important?

Brake balance ensures that both sides of an axle apply braking force evenly. An imbalance can lead to the vehicle pulling to one side during braking, reduced stopping power, and instability, posing a significant safety risk.

What happens if my brakes fail the test?

If your brakes fail to meet the required standards during a test, your vehicle will not pass the MOT. You will need to have the braking system repaired by a qualified mechanic and then present the vehicle for a re-test.

Conclusion

Understanding the different types of brake testers used in UK garages provides valuable insight into how your vehicle's braking system is assessed for safety and compliance. Whether it's the ubiquitous roller brake tester, the precise plate brake tester, or the handy decelerometer, each plays a role in ensuring your brakes are in optimal condition. Regular brake checks and maintenance are vital for your safety and the safety of others on the road.