Rear brake only, downhill, with a pillion
At 08:10 a rider leaves Aarhus for a commute. The route descends a 12% cobblestone hill that is wet from overnight rain. The rider carries a pillion passenger of 70 kg; the rider weighs 80 kg and the A2 motorcycle weighs 190 kg. At the top the rider is doing 45 km/h in third gear. A T-junction with a give-way line is at the bottom, and a bus is approaching from the right. The motorcycle has ABS. Because the front brake lever felt 'grabby' on a previous ride, the rider plans to use only the rear brake and engine braking. The rear tyre is inflated to the manufacturer's specification, but the cobblestones are slippery. The rider wants to stop before the give-way line.
1. Explain what is wrong with using only the rear brake and engine braking on this descent.
Read the worked answer
When a motorcycle slows, weight transfers forward. The front tyre gains load and therefore grip, while the rear tyre loses load. On a dry road the front brake can provide most of the stopping force. Using only the rear brake means the rider is relying on the tyre with the least load, and on a wet cobblestone descent that tyre can lock or step sideways very easily. Engine braking also acts only on the rear wheel and can cause the rear to skid if the rider downshifts abruptly. The result is a much longer stopping distance and a risk of a low-side fall, especially with a pillion adding mass. The front lever feeling 'grabby' is a reason to have the brake checked and to apply it progressively, not a reason to abandon it. On a slippery descent the rider needs smooth, progressive front braking more than ever, backed by a light rear brake.
2. How do the pillion and the downhill gradient change the braking problem?
Read the worked answer
The pillion adds 70 kg to a combined rider-and-bike mass of 270 kg, raising the total to 340 kg. That is about a 26% increase in mass, so for the same braking force the deceleration is lower and the stopping distance is longer. The pillion also raises the centre of gravity and changes the weight distribution; under braking the front load increases further, and the pillion can slide forward into the rider. The 12% downhill gradient adds a component of gravity along the direction of travel, so the brakes must absorb more energy and the bike accelerates if the rider releases them. The rear tyre may have more vertical load because of the pillion, but it is still not the best brake on a wet descent. The rider should allow a longer stopping distance, brake earlier, use a lower gear before the steep section, and keep the pillion informed so they brace against the tank rather than the rider.
3. Describe the braking technique the rider should use to stop before the give-way line.
Read the worked answer
Before the descent, select a lower gear so engine braking is helping without harsh downshifts. Keep the throttle closed, apply both brakes together, and build front-brake pressure progressively: initial light pressure to load the front tyre, then increasing pressure as the tyre takes the load. Use the rear brake lightly for stability, not as the main brake. Keep the motorcycle upright and the bars straight while braking; on wet cobblestones, avoid braking while leaned over. If the ABS pulses, keep the pressure on and do not release the lever. Look toward the give-way line and the bus, not down at the cobbles. If the bike is not slowing enough, release the brakes briefly, choose a lower gear, and reapply smoothly rather than grabbing more front brake. Stop before the line with enough margin to check the junction, then release the brakes and put a foot down only when stopped.