13-07-2019, 07:13 PM
It is interesting to think about the lowest speed that would allow a rider to stay on the wall without slipping off. The force arising from going round presses the tyres onto the wall and this means that the tyres can resist the downwards force gravity on the bike and rider. At some minimum speed this friction becomes smaller than the weight of the bike and rider so the bike will tend to slide off.
The minimum speed required to stay on the wall depends on the wall diameter. For a wall with a diameter of 10m (30ft) the minimum speed is about 20mph and for a wall of 37.5 metres, as Guy used in the record attempt, it is about 40mph. This is calculated using a coefficient of friction between hard rubber and wood of 0.7.
As the friction force that resists gravity acts where the tyre meets the wall, and the centre of gravity of the bike and rider is to one side of this, there is a tendency for the rider to be tipped off the bike. This is resisted by the rider leaning the bike a bit past the horizontal, as illustrated in the attached diagram.
The minimum speed required to stay on the wall depends on the wall diameter. For a wall with a diameter of 10m (30ft) the minimum speed is about 20mph and for a wall of 37.5 metres, as Guy used in the record attempt, it is about 40mph. This is calculated using a coefficient of friction between hard rubber and wood of 0.7.
As the friction force that resists gravity acts where the tyre meets the wall, and the centre of gravity of the bike and rider is to one side of this, there is a tendency for the rider to be tipped off the bike. This is resisted by the rider leaning the bike a bit past the horizontal, as illustrated in the attached diagram.