If you listen to a pilot and his crew debrief in a garage during a session, you will invariably hear a commentary on the chatter. It is a horseman’s oldest enemy because it steals trust. With the bike moving under them, they cannot open the throttle and the problem escalates the longer it continues. But what exactly is gossip? It is a harmonic imbalance created by the vibrations and frequencies on a motorcycle. Man and machine must be in perfect harmony to start a race, but it is sometimes the imperfect harmony of frequencies that can upset everything for them.
WHAT IS THE CAT?
âThe word chatter is used a lot, but most of the time it’s not strictly correct,â says Peter Bom, former Moto2 â¢ team leader and technical expert. âIt applies to anything that shakes and vibrates, but in the basic sense, the chatter was caused by the front or rear tire (or both). Improved tire construction has eliminated much of what was once called chatter. There seems to be a greater variety of chatter types now, starting at a lower frequency. “
With a rider that hangs on for life, they do whatever they can to make sure that while they’re on the track, they are squeezing every ounce of performance out of their bike. The only problem is that their bike is a vibration box that houses a 14,000 RPM motor running on a bumpy circuit with a 70kg rider bouncing side to side. The runner pushes as hard as he can, trying to go fast. But it takes them deep into the territory of oscillations. The harder you push a tire the more it slides instead of just rolling around the turn and even when we see a smooth, gradual slide it’s actually a continuous sequence of sliding and grip again in the corner. turn. This weekend in Assen we have a series of fast corners where this action will be repeated lap after lap.
This sliding sequence creates a vibration at a frequency that travels from the tire to the motorcycle and is usually dampened by the components of the motorcycle’s suspension. Chatter will develop for the rider if the frequency of this vibration coincides with the frequency of the complete bike, then resonance will occur and the two frequencies will amplify each other. These vibrations and movements all have an effect on performance and if not treated properly they can ruin a weekend or even a season. Racing is all about compromise. Bicycles should be rigid but flexible. They should be forgiving but also razor sharp.
NO EASY RESOLUTION
Chattering is the enemy of this compromise and therefore something to constantly think about. Every object in the world has a frequency when struck, but musical instruments give us the best example of how they can affect a racing motorcycle. If you pluck a guitar string, it releases a musical note. The guitar can release frequencies over a huge range, around 1300 hertz, making it as powerful a weapon for music as a WorldSBK bike is on its way. If you randomly select notes on the neck of the guitar, you will hear the differences between one note and the next. You can also feel it because the vibrations cause the pitch of the note. Beethoven was deaf but could still “feel” the music because of these vibrations.
A motorcycle is the same as a musical instrument. Vibrations caused by the engine or the environment all create their own notes. The key for a builder is to avoid frequencies that cause dangerous resonance that disrupts the bike. This is the natural effect of harmonics with their amplified frequency.
âIt’s kind of like when you wet your finger and slide it around the rim of a wine glass,â Bom continued. âThe glass will begin to vibrate, which will create an audible high-pitched sound. On a motorcycle, the rider may feel a high frequency vibration in their back or in their hands, while the motorcycle takes on a wider radius in the turn, in other words, it rolls wide.
Each object has natural resonant frequencies which can cause them to amplify the frequency. Bridges and buildings have collapsed because of this phenomenon – which is why armies will step on a bridge, for example – and the destructive power of that has the same effect on a motorcycle.
âChattering happens when there is relatively little ‘tension’ in the bike,â Bom explains. âIt often starts right after the rider releases the last brake pressure and goes away as soon as he opens the throttle again. So especially during the taxiing phase. It costs lap time, but doesn’t knock you down.
The easiest remedy for this on a bicycle? Change the frequency by pressing the accelerator or adding a brake button: âPilots can influence it themselves,â says Peter Bom. âKeeping the tension on the bike longer or using a different line can make a big difference. Riding style can make a big difference and that’s why a driver like Jorge Lorenzo would have more problems riding in chatter than a driver like Casey Stoner.
Like playing the guitar and going up the neck, you increase the tension on the string and change the frequency of the bike when you open or close the throttle. The goal on a racing bike is to tighten the rope by accelerating and forcing the center of gravity towards the rear of the bike. Easier said than done however for a rider with the bike rearing up under him due to chatter forces and pushing them out of line. Opening the throttle could, however, make matters worse and cause an accident. The cure can be worse than the ailment. Sometimes it’s better to eliminate the chatter and suck up the waste of time.
How do you solve it in WorldSBK?
In today’s era of aerodynamics in WorldSBK, the last key to solving problems may come from the fairings of the bikes. Ultra-light carbon fiber seat stays are crucial for performance, but depending on how the wind hits the fairing it can have a big effect on what happens with the bike. Does this air move cleanly on the bike, or does it cause a downstream effect on another part? How to reduce the effects of gossip? There are many ways around it, ranging from riding style and body positioning on the bike to teams adding weights to different parts of the bike to ensure that frequencies from certain parts can be knocked out. This is equivalent to adjusting your style on the guitar. Instead of a hard strum, you can reduce the force and suddenly the notes are the same but sharper.
However, there is no guarantee: âIn terms of solutions, I saw all the suggestions under the sun,â says Peter Bom. âYou wouldn’t believe it. The problem is that a solution may work today but not tomorrow. You want to reduce the chances of resonance starting, but hundreds of components are involved. ‘extreme damping, etc. If you had a choice you would struggle, then use a different tire and try to get the most out of it. Sometimes you don’t have that luxury, however. A chatter-sensitive tire would always start. to chatting more as he wore, a new one was OK for a little while. In summary, a team leader is constantly fighting to try to make the notes of his instrument sing, sometimes it means harsh words with the pilot but in in most cases it is about finding a compromise.
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