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A lap of the Twin Ring Motegi circuit

A lap of the Twin Ring Motegi circuit

A lap of the Twin Ring Motegi circuit

The two main characteristics of the Motegi circuit are rapid accelerations and sharp braking. At Twin-Ring Motegi there are six areas of acceleration where the bike goes from under 100 Km/h to over 230Km/h and in three of these straights speeds of more than 260 Km/h are registered. Elsewhere there are four areas of braking where the bike decreases from over 250 km/h to less than 90 Km/h.

These characteristics influence the set-up of the bikes for the Japanese GP. With the braking areas mentioned, and taking into account that for 40 % of the lap the bike is decelerating, it is essential to find stability under braking and a correctly-adjusted engine brake - in particular to avoid the rear wheel locking up - to gain fast times. To achieve this more weight is added to the rear of the bike than is usual which also increases grip under acceleration.

As is normally the case, this weight adjustment does cause other problems, in particular ‘wheelies', where the front wheel loses contact with the track surface. Since the accelerations begin from low speeds, the first and second gear ratios are relatively short which also increases the tendency to do wheelies, making the bike more difficult to control. Often when this happens the riders must close the throttle to regain control of the bike. What's more, since braking is often sharp, the front springs fitted are normally firm meaning that the front of the bike sits higher than normal.

With more weight in the rear of the bike under acceleration, the front end becomes lighter and this can lead to chattering in the front wheel, especially in the esses. Gearbox settings are another critical factor at Motegi: all gears are used at one point or another on the circuit and, since the first is short and the sixth relatively long, it is vital to set the correct ratios to avoid falling out of the power delivery zone. First gear is used in corners, ‘5', ‘V-Corner' and ‘Hairpin'. Second gear is used to negotiate corners ‘2', ‘3', ‘4', ‘90º corner' and ‘Victory Corner'. The ‘S-Curves' are taken in third and the ‘130R' in fourth.

When finding the right engine settings you must take into account that 25% of the lap is taken with the throttle fully open which clearly affects fuel consumption. As a result of this, the race distance has been reduced from 25 laps as it was three seasons ago to 24 following the introduction of the MotoGP four-stroke bikes, as it proved impossible for these bikes to complete the twenty seven laps (2+25) using the 24 litres of fuel that regulations permitted.

The accelerations and braking at this circuit influence the composition of the tyres used. At many circuits, the rear wheel becomes worn on one side, depending on the amount of left or right-handed corners, however, at Motegi the centre section of the rear tyre becomes most easily worn. The constant acceleration and the long straights at the circuit mean that centre section of the tyre is manufactured with a harder compound than the lateral sections. The front tyre choice is also crucial since the constant braking also makes the tyre suffer heavier than normal wear in the centre section.

Another special setting to be decided at this circuit is the size of the front brake discs to ensure that the brakes perform correctly throughout the 24 laps of the race. With the numerous braking points at this circuit, many riders choose to fit larger discs than normal.

Tags:
MotoGP, 2005, GRAND PRIX OF JAPAN

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