Rain and wet

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Rain and wet
Jahn

Sports & scene

Rain and wet

Less grip, more caution
Driving in rain and wet

Riding a motorcycle in the rain cannot always be avoided in this country. But with the right equipment and a realistic basic posture, a ride in the rain can also be managed safely and relaxed.

Nicolas Streblow

02.03.2018

Video: Riding a motorcycle in the wet

Most motorcyclists dream of having a dry, winding road with the finest asphalt all to themselves. Unfortunately, the reality in our part of the world looks very different. Because you can often choose neither the weather nor the degree of filling of the streets, if you want to move a little further away from the garage at home.

Rain is nasty, but not a big problem with good tires and clothing. Dry and, thanks to the anti-fog visor, also with good visibility, we should still slow down, because the wetness and lower temperatures mean that we have noticeably less grip available. Road markings and bitumen strips, cobblestones and manhole covers are even more slippery than when it is dry.

In addition, when we are wet, we cannot perceive such nasty traps as we may later even not notice an oil trail and the like. In dry phases, a lot of oil, dust and rubber debris are deposited in the pavement pores. The next time it rains, these substances are moistened and act like soft soap. Shortly after the start of the rain it is therefore slipperiest, and after a day of continuous rain the grip has often improved again.

Bends that can be taken with easy turns in the dry require sensitive use of the accelerator and brakes in the wet. When it rains, choosing the right line in curves is even more important than on a dry road. The trend is for a defensive driving style and a smooth, rounded driving style, at the same time good training for fine motor skills and concentration. The driving dynamics work no differently in the rain than on a dry road – with the crucial difference that processes such as accelerating, braking, turning and cornering have to be much smoother.

Anyone who turns sharply, brakes in a frightful manner or hastily turns the accelerator can suddenly overwhelm the tire grip on wet roads. Even when downshifting and engaging the clutch (tip: double-declutching!) You should go to work more gently; It is better to select a gear higher in the bends in order to accelerate smoothly and evenly from a lean angle with less speed.

In all of this, the following applies: stay relaxed. Especially when changing from dry to wet road surfaces, many people tend to tense up. And if you tense up, you will feel the motorcycle’s reactions later, maybe too late. In order to arrive safely in the rain, you should always consciously relax: drop your shoulders, loosen your upper lip, loosen your hands a little, take the tension off your buttocks. And maybe take a break and choose the pace so that you still feel comfortable despite the wetness. We recommend training under professional guidance in which braking maneuvers and cornering on wet, artificially watered road surfaces are practiced intensively.

To prevent the front wheel from slipping on the wet asphalt when braking hard, you have to pull the brake lever more carefully and build up the brake pressure quickly, but a little more slowly than in dry conditions. Stay a little below the personal, trained maximum value. Important: brake hard at the rear. Braking decelerations of up to 8.0 m / sec² can be achieved on non-slip asphalt. This corresponds to a braking distance from 100 km / h of 48 meters, i.e. only around eight meters longer than in the dry. However, the risk of the front wheel locking is relatively high, which requires a quick release and gripping. Or an effective ABS that can achieve amazing deceleration values ​​in rain or on a slippery road surface.

Rain and wet

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Bends in the wet: drive soft lines


Rain and wet


Illustration: Muller

Curves are pretty tricky when wet. Stop braking before the bend and turn in gently. Set the imaginary apex late so that there is enough space to accelerate gently. It is dangerous to live on the wrong line (dashed), especially since the asphalt there is often polished smooth by car tires and offers less grip.

The measured values ​​of a Honda CBR 600 F show how different road surfaces in the rain affect the braking distance and the possible lean angle. The braking distance is hardly longer on grippy racetrack asphalt than on dry slopes. On the wet country road, however, the sports touring bike needs 77 meters to brake hard from 100 km / h, and significantly more if the surface is poor. In addition, the possible inclination is drastically reduced.

Coefficient of friction

Braking distance 100-0 km / h

Inclined position Wet race track 0.8 48 meters 39 degrees Wet country road 0.5 77 meters 27 degrees Wet cobblestones 0.3 128 meters 17 degrees Very dirty 0.2 193 meters 11 degrees

(with very adhesive road sport tires)

Wet roads: danger of slipping


Rain and wet


Illustraition: Muller

The macrorough elevations in the asphalt store the rainwater, but only the microrough tips, which drill through the water film and thus establish contact, ensure a good grip and toothing.

In wet conditions, the grip of the tires drops dramatically, which means that significantly less lean angle is possible than on a dry road.

However, it depends very much on the road surface. In a coarse surface with fine tips (technical term: microrough), the tire can interlock perfectly and even in wet conditions allows proper inclines, as can be marveled at over and over again in rainy races.

On the other hand, coarse surfaces with smooth edges (technical term: macrorough) such as cobblestones displace the film of water, but the interlocking and thus the tire grip are poor, and the possible inclination is greatly reduced.

Tire grip in the rain


Rain and wet


Illustration: Muller

The edges of the profile blocks work in a similar way. The rubber block is displaced by lateral forces and the edges are pressed onto the asphalt by the film of water. This is why tires wear out the most on the edges of the tread.

The tire tread is also extremely important when it is wet, as the water is transported to the outside via the tread grooves and a high pressure builds up on the edge of the tread block. This is the only way to break through the film of water and establish contact with the road.

Silica plays a major role in this context and is now added to many tires. In addition to other good properties, it ensures the necessary elasticity, even at low temperatures, in order to interlock with the micro-rough asphalt peaks.

Aquaplaning on a motorcycle


Rain and wet


Illustration: Muller

When the water level is high, a water wedge forms in front of the front wheel, which is pushed between the tire and the road surface. If the water pressure is higher than the contact pressure of the tire, aquaplaning occurs.

Advantage for the motorcycle: Compared to the wide car tires (right), the motorcycle tire (left) has a smaller contact area and – more importantly – a rounded contour. This pushes the water wedge to the side, the tire pushes through the water front, and the risk of aquaplaning is reduced. The flat contour of the car tire, on the other hand, creates a wide water front directly in the direction of travel.

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