We have all heard about g-force, that measure of acceleration that allows you to measure the force that vehicles and human beings are subject to in certain acceleration or deceleration (braking) moments. In the 17th century, Isaac Newton wrote his second law, known as the Law of Acceleration, in which he formulated the equation that this physical moment is defined: F=ma. Where F is force, m is mass, and a is acceleration. Delving into the effects of acceleration on a human body, Newton set out another equation to measure the magnitude of that force: F=mg, where g is gravity. Acceleration and g-force are similar terms, and a force of 1 g represents an acceleration of 9.72 m/s.
Without going further into physics terminology, we tend to summarize the g-force effect by multiplying the weight of the mass by the magnitude of the g-force applied to it. In other words, for example, a force of 3 g represents three times the weight of the mass to which it is applied.
In what way do g-forces affect MotoGP riders?
It must be said that, fortunately, riders aren’t usually subject to forces of a high magnitude, but sometimes accidents do involve huge impacts of very high intensity. We can’t forget the accident suffered by Jorge Martín in Portimao in 2021, where it reached a peak of 26 g. And it wasn’t the highest since impact records began, thanks to the collaboration of the equipment manufacturers, which have developed increasingly sophisticated protective equipment, such as race suits with airbags, which are responsible for registering this data. In 2019, Marc Márquez had a fall in Sepang that reached 26.27 g, and three years before at the same location, Loris Baz had an accident whose impact peak reached 29.9 g.
Nowhere near the highest historical record documented in a motor sport event, when the Brit David Purley suffered an accident in 1977 at Silverstone, during practice at the Formula 1 British Grand Prix. Purley, at the wheel of a LEC-Ford, hit a wall at 173 km/h, stopping in only 66 centimeters and registering a force of 179 g. He would ride again two years later.
The g-force effect is reflected much more in the riders of cars than bikes because the former form a whole with the mass of the car. MotoGP riders, due to the power, acceleration, and speed that they reach, are the motorcyclists most affected by g-force.
The most critical moment is the braking, because they sometimes have to cope with huge decelerations. According to studies carried out by Brembo, the manufacturer of the brakes fitted on all MotoGP bikes, the average g-force of World Championship circuits is around 1.1 or 1.2 g, and when it surpasses 1.4 g, the manufacturer considers it a high deceleration average.
Is it normal to find braking above this high average in MotoGP? Well although it doesn’t seem like it, it is a common occurrence. All circuits on the calendar have at least one braking of 1.5 g, and some tracks, such as the Austrian Red Bull Ring, the Twin Ring Motegi of Japan, and the Buriram circuit in Thailand, have several braking with this intensity. The situation is so critical that it can compromise the performance of the brakes, so the use of a large-diameter brake disc is compulsory in these tracks. Normally 320-mm discs are used, but in these three circuits 340-mm discs or even 355-mm discs must be used. Its bigger diameter doesn’t imply a greater g-force effect, but they are used to ensure optimum functioning over many laps.
However, the highest g-force point in the whole championship is in the Portimao circuit: in the braking of turn 1, a force of 1.8 g is reached. In addition to the enormous speed reached at the end of the straight (336 km/h), there is also a steep downhill gradient at the braking point, which increases the load. The 1.7 g reached on the first turn of the Circuit Ricardo Tormo can’t be overlooked either, where a high speed is also reached, 325 km/h.
High g-force loads can also be recorded during turning, although in this case the bikes don’t suffer it the same way as cars. In the bikes, the g-force is split because of the different dynamic of the vehicles. While the car and the driver form a single mass and move in the same plane, in a motorcycle, the vehicle and the rider act differently.
The simple fact of the inclination when tackling a turn serves to split the forces, because the centrifugal force, the centripetal force, and the g-force itself coincide at the same moment of acceleration. In other words, that when tackling a turn there is a force that tends to follow the inertia of the mass (centrifugal force), against which the rider fights, driving the motorcycle towards the desired trajectory (centripetal force). The conjunction of both moments splits the g-force effect in turns.